Network Working Group D. Pinkas
Request for Comments: 5126 Bull SAS
Obsoletes: 3126 N. Pope
Category: Informational Thales eSecurity
J. Ross
Security and Standards
February 2008
CMS Advanced Electronic Signatures (CAdES)
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Abstract
This document defines the format of an electronic signature that can
remain valid over long periods. This includes evidence as to its
validity even if the signer or verifying party later attempts to deny
(i.e., repudiates) the validity of the signature.
The format can be considered as an extension to RFC 3852 and RFC
2634, where, when appropriate, additional signed and unsigned
attributes have been defined.
The contents of this Informational RFC amount to a transposition of
the ETSI Technical Specification (TS) 101 733 V.1.7.4 (CMS Advanced
Electronic Signatures -- CAdES) and is technically equivalent to it.
The technical contents of this specification are maintained by ETSI.
The ETSI TS and further updates are available free of charge at:
http://www.etsi.org/WebSite/Standards/StandardsDownload.aspx
Pinkas, et al. Informational [Page 1]RFC 5126 CMS Advanced Electronic Signatures February 2008
Table of Contents
1. Introduction ....................................................6
2. Scope ...........................................................6
3. Definitions and Abbreviations ...................................8
3.1. Definitions ................................................8
3.2. Abbreviations .............................................11
4. Overview .......................................................12
4.1. Major Parties .............................................13
4.2. Signature Policies ........................................14
4.3. Electronic Signature Formats ..............................15
4.3.1. CAdES Basic Electronic Signature (CAdES-BES) .......15
4.3.2. CAdES Explicit Policy-based Electronic
Signatures (CAdES-EPES) ............................18
4.4. Electronic Signature Formats with Validation Data .........19
4.4.1. Electronic Signature with Time (CAdES-T) ...........20
4.4.2. ES with Complete Validation Data References
(CAdES-C) ..........................................21
4.4.3. Extended Electronic Signature Formats ..............23
4.4.3.1. EXtended Long Electronic Signature
(CAdES-X Long) ............................24
4.4.3.2. EXtended Electronic Signature with
Time Type 1 ...............................25
4.4.3.3. EXtended Electronic Signature with
Time Type 2 ...............................26
4.4.3.4. EXtended Long Electronic Signature
with Time (CAdES-X Long ...................27
4.4.4. Archival Electronic Signature (CAdES-A) ............27
4.5. Arbitration ...............................................28
4.6. Validation Process ........................................29
5. Electronic Signature Attributes ................................30
5.1. General Syntax ............................................30
5.2. Data Content Type .........................................30
5.3. Signed-data Content Type ..................................30
5.4. SignedData Type ...........................................31
5.5. EncapsulatedContentInfo Type ..............................31
5.6. SignerInfo Type ...........................................31
5.6.1. Message Digest Calculation Process .................32
5.6.2. Message Signature Generation Process ...............32
5.6.3. Message Signature Verification Process .............32
5.7. Basic ES Mandatory Present Attributes .....................32
5.7.1. content-type .......................................32
5.7.2. Message Digest .....................................33
5.7.3. Signing Certificate Reference Attributes ...........33
5.7.3.1. ESS signing-certificate Attribute
Definition ................................34
5.7.3.2. ESS signing-certificate-v2
Attribute Definition ......................34
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5.7.3.3. Other signing-certificate
Attribute Definition ......................35
5.8. Additional Mandatory Attributes for Explicit
Policy-based Electronic Signatures ........................36
5.8.1. signature-policy-identifier ........................36
5.9. CMS Imported Optional Attributes ..........................38
5.9.1. signing-time .......................................38
5.9.2. countersignature ...................................39
5.10. ESS-Imported Optional Attributes .........................39
5.10.1. content-reference Attribute .......................39
5.10.2. content-identifier Attribute ......................39
5.10.3. content-hints Attribute ...........................40
5.11. Additional Optional Attributes Defined in the
Present Document .........................................40
5.11.1. commitment-type-indication Attribute ..............41
5.11.2. signer-location Attribute .........................43
5.11.3. signer-attributes Attribute .......................43
5.11.4. content-time-stamp Attribute ......................44
5.12. Support for Multiple Signatures ..........................44
5.12.1. Independent Signatures ............................44
5.12.2. Embedded Signatures ...............................45
6. Additional Electronic Signature Validation Attributes ..........45
6.1. signature time-stamp Attribute (CAdES-T) ..................47
6.1.1. signature-time-stamp Attribute Definition ..........47
6.2. Complete Validation Data References (CAdES-C) .............48
6.2.1. complete-certificate-references Attribute
Definition .........................................48
6.2.2. complete-revocation-references Attribute
Definition .........................................49
6.2.3. attribute-certificate-references Attribute
Definition .........................................51
6.2.4. attribute-revocation-references Attribute
Definition .........................................52
6.3. Extended Validation Data (CAdES-X) ........................52
6.3.1. Time-Stamped Validation Data (CAdES-X Type
1 or Type 2) .......................................53
6.3.2. Long Validation Data (CAdES-X Long, CAdES-X
Long Type 1 or 2) ..................................53
6.3.3. certificate-values Attribute Definition ............54
6.3.4. revocation-values Attribute Definition .............54
6.3.5. CAdES-C-time-stamp Attribute Definition ............56
6.3.6. time-stamped-certs-crls-references
Attribute Definition ...............................57
6.4. Archive Validation Data ...................................58
6.4.1. archive-time-stamp Attribute Definition ............58
7. Other Standard Data Structures .................................60
7.1. Public Key Certificate Format .............................60
7.2. Certificate Revocation List Format ........................60
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7.3. OCSP Response Format ......................................60
7.4. Time-Stamp Token Format ...................................60
7.5. Name and Attribute Formats ................................60
7.6. AttributeCertificate ......................................61
8. Conformance Requirements .......................................61
8.1. CAdES-Basic Electronic Signature (CAdES-BES) ..............62
8.2. CAdES-Explicit Policy-based Electronic Signature ..........63
8.3. Verification Using Time-Stamping ..........................63
8.4. Verification Using Secure Records .........................63
9. References .....................................................64
9.1. Normative References ......................................64
9.2. Informative References ....................................65
Annex A (normative): ASN.1 Definitions ............................69
A.1. Signature Format Definitions Using
X.208 ASN.1 Syntax ...................................69
A.2. Signature Format Definitions Using
X.680 ASN.1 Syntax ...................................77
Annex B (informative): Extended Forms of Electronic Signatures ....86
B.1. Extended Forms of Validation Data ....................86
B.1.1. CAdES-X Long ..................................87
B.1.2. CAdES-X Type 1 ................................88
B.1.3. CAdES-X Type 2 ................................90
B.1.4. CAdES-X Long Type 1 and CAdES-X Long Type 2 ...91
B.2. Time-Stamp Extensions ................................93
B.3. Archive Validation Data (CAdES-A) ....................94
B.4. Example Validation Sequence ..........................97
B.5. Additional Optional Features ........................102
Annex C (informative): General Description .......................103
C.1. The Signature Policy ................................103
C.2. Signed Information ..................................104
C.3. Components of an Electronic Signature ...............104
C.3.1. Reference to the Signature Policy ............104
C.3.2. Commitment Type Indication ...................105
C.3.3. Certificate Identifier from the Signer .......106
C.3.4. Role Attributes ..............................106
C.3.4.1. Claimed Role .......................107
C.3.4.2. Certified Role .....................107
C.3.5. Signer Location ..............................108
C.3.6. Signing Time .................................108
C.3.7. Content Format ...............................108
C.3.8. content-hints ................................109
C.3.9. Content Cross-Referencing ....................109
C.4. Components of Validation Data .......................109
C.4.1. Revocation Status Information ................109
C.4.1.1. CRL Information .....................110
C.4.1.2. OCSP Information ....................110
C.4.2. Certification Path ...........................111
C.4.3. Time-stamping for Long Life of Signatures ....111
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C.4.4. Time-stamping for Long Life of Signature
before CA key Compromises ....................113
C.4.4.1. Time-stamping the ES with
Complete Validation Data ...........113
C.4.4.2. Time-Stamping Certificates and
Revocation Information References ..114
C.4.5. Time-stamping for Archive of Signature .......115
C.4.6. Reference to Additional Data .................116
C.4.7. Time-Stamping for Mutual Recognition .........116
C.4.8. TSA Key Compromise ...........................117
C.5. Multiple Signatures .................................118
Annex D (informative): Data Protocols to Interoperate with TSPs ..118
D.1. Operational Protocols ...............................118
D.1.1. Certificate Retrieval ........................118
D.1.2. CRL Retrieval ................................118
D.1.3. Online Certificate Status ....................119
D.1.4. Time-Stamping ................................119
D.2. Management Protocols ................................119
D.2.1. Request for Certificate Revocation ...........119
Annex E (informative): Security Considerations ...................119
E.1. Protection of Private Key ...........................119
E.2. Choice of Algorithms ................................119
Annex F (informative): Example Structured Contents and MIME ......120
F.1. General Description .................................120
F.1.1. Header Information ...........................120
F.1.2. Content Encoding .............................121
F.1.3. Multi-Part Content ...........................121
F.2. S/MIME ..............................................122
F.2.1. Using application/pkcs7-mime .................123
F.2.2. Using application/pkcs7-signature ............124
Annex G (informative): Relationship to the European Directive
and EESSI .................................125
G.1. Introduction ........................................125
G.2. Electronic Signatures and the Directive .............126
G.3. ETSI Electronic Signature Formats and the Directive .127
G.4. EESSI Standards and Classes of Electronic Signature .127
G.4.1. Structure of EESSI Standardization ...........127
G.4.2. Classes of Electronic Signatures .............128
G.4.3. Electronic Signature Classes and the ETSI
Electronic Signature Format ..................128
Annex H (informative): APIs for the Generation and Verification
of Electronic Signatures Tokens ...........129
H.1. Data Framing ........................................129
H.2. IDUP-GSS-APIs Defined by the IETF ...................131
H.3. CORBA Security Interfaces Defined by the OMG ........132
Annex I (informative): Cryptographic Algorithms ..................133
I.1. Digest Algorithms ...................................133
I.1.1. SHA-1 ........................................133
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I.1.2. General ......................................133
I.2. Digital Signature Algorithms ........................134
I.2.1. DSA ..........................................134
I.2.2. RSA ..........................................135
I.2.3. General ......................................135
Annex J (informative): Guidance on Naming ........................137
J.1. Allocation of Names .................................137
J.2. Providing Access to Registration Information ........138
J.3. Naming Schemes ......................................138
J.3.1. Naming Schemes for Individual Citizens .......138
J.3.2. Naming Schemes for Employees of an
Organization .................................139
1. Introduction
This document is intended to cover electronic signatures for various
types of transactions, including business transactions (e.g.,
purchase requisition, contract, and invoice applications) where
long-term validity of such signatures is important. This includes
evidence as to its validity even if the signer or verifying party
later attempts to deny (i.e., repudiates; see ISO/IEC 10181-5
[ISO10181-5]) the validity of the signature.
Thus, the present document can be used for any transaction between an
individual and a company, between two companies, between an
individual and a governmental body, etc. The present document is
independent of any environment; it can be applied to any environment,
e.g., smart cards, Global System for Mobile Communication Subscriber
Identity Module (GSM SIM) cards, special programs for electronic
signatures, etc.
The European Directive on a community framework for Electronic
Signatures defines an electronic signature as: "Data in electronic
form which is attached to or logically associated with other
electronic data and which serves as a method of authentication".
An electronic signature, as used in the present document, is a form
of advanced electronic signature, as defined in the Directive.
2. Scope
The scope of the present document covers electronic signature formats
only. The aspects of Electronic Signature Policies are defined in
RFC 3125 [RFC3125] and ETSI TR 102 272 [TR102272].
The present document defines a number of electronic signature
formats, including electronic signatures that can remain valid over
long periods. This includes evidence as to its validity even if the
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signer or verifying party later attempts to deny (repudiates) the
validity of the electronic signature.
The present document specifies use of Trusted Service Providers
(e.g., Time-Stamping Authorities) and the data that needs to be
archived (e.g., cross-certificates and revocation lists) to meet the
requirements of long-term electronic signatures.
An electronic signature, as defined by the present document, can be
used for arbitration in case of a dispute between the signer and
verifier, which may occur at some later time, even years later.
The present document includes the concept of signature policies that
can be used to establish technical consistency when validating
electronic signatures, but it does not mandate their use.
The present document is based on the use of public key cryptography
to produce digital signatures, supported by public key certificates.
The present document also specifies the use of time-stamping and
time-marking services to prove the validity of a signature long after
the normal lifetime of critical elements of an electronic signature.
This document also, as an option, defines ways to provide very
long-term protection against key compromise or weakened algorithms.
The present document builds on existing standards that are widely
adopted. These include:
- RFC 3852 [4]: "Cryptographic Message Syntax (CMS)";
- ISO/IEC 9594-8/ITU-T Recommendation X.509 [1]: "Information
technology - Open Systems Interconnection - The Directory:
Authentication framework";
- RFC 3280 [2]: "Internet X.509 Public Key Infrastructure (PKIX)
Certificate and Certificate Revocation List (CRL) Profile";
- RFC 3161 [7]: "Internet X.509 Public Key Infrastructure
Time-Stamp Protocol (TSP)".
NOTE: See Section 11 for a full set of references.
The present document describes formats for advanced electronic
signatures using ASN.1 (Abstract Syntax Notation 1) [14]. ASN.1 is
encoded using X.690 [16].
These formats are based on CMS (Cryptographic Message Syntax) defined
in RFC 3852 [4]. These electronic signatures are thus called CAdES,
for "CMS Advanced Electronic Signatures".
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Another document, TS 101 903 [TS101903], describes formats for XML
advanced electronic signatures (XAdES) built on XMLDSIG as specified
in [XMLDSIG].
In addition, the present document identifies other documents that
define formats for Public Key Certificates, Attribute Certificates,
and Certificate Revocation Lists and supporting protocols, including
protocols for use by trusted third parties to support the operation
of electronic signature creation and validation.
Informative annexes include:
- illustrations of extended forms of Electronic Signature formats
that protect against various vulnerabilities and examples of
validation processes (Annex B);
- descriptions and explanations of some of the concepts used in
the present document, giving a rationale for normative parts of
the present document (Annex C);
- information on protocols to interoperate with Trusted Service
Providers (Annex D);
- guidance on naming (Annex E);
- an example structured content and MIME (Annex F);
- the relationship between the present document and the directive
on electronic signature and associated standardization
initiatives (Annex G);
- APIs to support the generation and verification of electronic
signatures (Annex H);
- cryptographic algorithms that may be used (Annex I); and
- naming schemes (see Annex J).
3. Definitions and Abbreviations
3.1. Definitions
For the purposes of the present document, the following terms and
definitions apply:
Arbitrator: an arbitrator entity may be used to arbitrate a dispute
between a signer and verifier when there is a disagreement on the
validity of a digital signature.
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Attribute Authority (AA): an authority that assigns privileges by
issuing attribute certificates.
Authority Certificate: a certificate issued to an authority (e.g.,
either to a certification authority or an attribute authority).
Attribute Authority Revocation List (AARL): a revocation list
containing a list of references to certificates issued to AAs that
are no longer considered valid by the issuing authority.
Attribute Certificate Revocation List (ACRL): a revocation list
containing a list of references to attribute certificates that are no
longer considered valid by the issuing authority.
Certification Authority Revocation List (CARL): a revocation list
containing a list of public key certificates issued to certification
authorities that are no longer considered valid by the certificate
issuer.
Certification Authority (CA): an authority trusted by one or more
users to create and assign public key certificates; optionally, the
certification authority may create the users' keys.
NOTE: See ITU-T Recommendation X.509 [1].
Certificate Revocation List (CRL): a signed list indicating a set of
public key certificates that are no longer considered valid by the
certificate issuer.
Digital Signature: data appended to, or a cryptographic
transformation of, a data unit that allows a recipient of the data
unit to prove the source and integrity of the data unit and protect
against forgery, e.g., by the recipient.
NOTE: See ISO 7498-2 [ISO7498-2].
Electronic Signature: data in electronic form that is attached to or
logically associated with other electronic data and that serves as a
method of authentication.
NOTE: See Directive 1999/93/EC of the European Parliament and of
the Council of 13 December 1999 on a Community framework for
electronic signatures [EUDirective].
Extended Electronic Signatures: electronic signatures enhanced by
complementing the baseline requirements with additional data, such as
time-stamp tokens and certificate revocation data, to address
commonly recognized threats.
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Explicit Policy-based Electronic Signature (EPES): an electronic
signature where the signature policy that shall be used to validate
it is explicitly specified.
Grace Period: a time period that permits the certificate revocation
information to propagate through the revocation process to relying
parties.
Initial Verification: a process performed by a verifier done after an
electronic signature is generated in order to capture additional
information that could make it valid for long-term verification.
Public Key Certificate (PKC): public keys of a user, together with
some other information, rendered unforgeable by encipherment with the
private key of the certification authority that issued it.
NOTE: See ITU-T Recommendation X.509 [1].
Rivest-Shamir-Adleman (RSA): an asymmetric cryptography algorithm
based on the difficulty to factor very large numbers using a key
pair: a private key and a public key.
Signature Policy: a set of rules for the creation and validation of
an electronic signature that defines the technical and procedural
requirements for electronic signature creation and validation, in
order to meet a particular business need, and under which the
signature can be determined to be valid.
Signature Policy Issuer: an entity that defines and issues a
signature policy.
Signature Validation Policy: part of the signature policy that
specifies the technical requirements on the signer in creating a
signature and verifier when validating a signature.
Signer: an entity that creates an electronic signature.
Subsequent Verification: a process performed by a verifier to assess
the signature validity.
NOTE: Subsequent verification may be done even years after the
electronic signature was produced by the signer and completed by
the initial verification, and it might not need to capture more
data than those captured at the time of initial verification.
Time-Stamp Token: a data object that binds a representation of a
datum to a particular time, thus establishing evidence that the datum
existed before that time.
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Time-Mark: information in an audit trail from a Trusted Service
Provider that binds a representation of a datum to a particular time,
thus establishing evidence that the datum existed before that time.
Time-Marking Authority: a trusted third party that creates records in
an audit trail in order to indicate that a datum existed before a
particular point in time.
Time-Stamping Authority (TSA): a trusted third party that creates
time-stamp tokens in order to indicate that a datum existed at a
particular point in time.
Time-Stamping Unit (TSU): a set of hardware and software that is
managed as a unit and has a single time-stamp token signing key
active at a time.
Trusted Service Provider (TSP): an entity that helps to build trust
relationships by making available or providing some information upon
request.
Validation Data: additional data that may be used by a verifier of
electronic signatures to determine that the signature is valid.
Valid Electronic Signature: an electronic signature that passes
validation.
Verifier: an entity that verifies evidence.
NOTE 1: See ISO/IEC 13888-1 [ISO13888-1].
NOTE 2: Within the context of the present document, this is an
entity that validates an electronic signature.
3.2. Abbreviations
For the purposes of the present document, the following abbreviations
apply:
AA Attribute Authority
AARL Attribute Authority Revocation List
ACRL Attribute Certificate Revocation List
API Application Program Interface
ASCII American Standard Code for Information Interchange
ASN.1 Abstract Syntax Notation 1
CA Certification Authority
CAD Card Accepting Device
CAdES CMS Advanced Electronic Signature
CAdES-A CAdES with Archive validation data
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CAdES-BES CAdES Basic Electronic Signature
CAdES-C CAdES with Complete validation data
CAdES-EPES CAdES Explicit Policy Electronic Signature
CAdES-T CAdES with Time
CAdES-X CAdES with eXtended validation data
CAdES-X Long CAdES with EXtended Long validation data
CARL Certification Authority Revocation List
CMS Cryptographic Message Syntax
CRL Certificate Revocation List
CWA CEN (European Committee for Standardization) Workshop
Agreement
DER Distinguished Encoding Rules (for ASN.1)
DSA Digital Signature Algorithm
EDIFACT Electronic Data Interchange For Administration,
Commerce and Transport
EESSI European Electronic Signature Standardization
Initiative
EPES Explicit Policy-based Electronic Signature
ES Electronic Signature
ESS Enhanced Security Services (enhances CMS)
IDL Interface Definition Language
MIME Multipurpose Internet Mail Extensions
OCSP Online Certificate Status Provider
OID Object IDentifier
PKC Public Key Certificate
PKIX Public Key Infrastructure using X.509
(IETF Working Group)
RSA Rivest-Shamir-Adleman
SHA-1 Secure Hash Algorithm 1
TSA Time-Stamping Authority
TSP Trusted Service Provider
TST Time-Stamp Token
TSU Time-Stamping Unit
URI Uniform Resource Identifier
URL Uniform Resource Locator
XML Extensible Markup Language
XMLDSIG XML Digital Signature
4. Overview
The present document defines a number of Electronic Signature (ES)
formats that build on CMS (RFC 3852 [4]) by adding signed and
unsigned attributes.
This section:
- provides an introduction to the major parties involved
(Section 4.1),
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- introduces the concept of signature policies (Section 4.2),
- provides an overview of the various ES formats (Section 4.3),
- introduces the concept of validation data, and provides an
overview of formats that incorporate validation data
(Section 4.4), and
- presents relevant considerations on arbitration
(Section 4.5) and for the validation process (Section 4.6).
The formal specifications of the attributes are specified in Sections
5 and 6; Annexes C and D provide rationale for the definitions of the
different ES forms.
4.1. Major Parties
The major parties involved in a business transaction supported by
electronic signatures, as defined in the present document, are:
- the signer;
- the verifier;
- Trusted Service Providers (TSP); and
- the arbitrator.
The signer is the entity that creates the electronic signature. When
the signer digitally signs over data using the prescribed format,
this represents a commitment on behalf of the signing entity to the
data being signed.
The verifier is the entity that validates the electronic signature;
it may be a single entity or multiple entities.
The Trusted Service Providers (TSPs) are one or more entities that
help to build trust relationships between the signer and verifier.
They support the signer and verifier by means of supporting services
including: user certificates, cross-certificates, time-stamp tokens,
CRLs, ARLs, and OCSP responses. The following TSPs are used to
support the functions defined in the present document:
- Certification Authorities;
- Registration Authorities;
- CRL Issuers;
- OCSP Responders;
- Repository Authorities (e.g., a Directory);
- Time-Stamping Authorities;
- Time-Marking Authorities; and
- Signature Policy Issuers.
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Certification Authorities provide users with public key certificates
and a revocation service.
Registration Authorities allow the identification and registration of
entities before a CA generates certificates.
Repository Authorities publish CRLs issued by CAs, signature policies
issued by Signature Policy Issuers, and optionally public key
certificates.
Time-Stamping Authorities attest that some data was formed before a
given trusted time.
Time-Marking Authorities record that some data was formed before a
given trusted time.
Signature Policy Issuers define the signature policies to be used by
signers and verifiers.
In some cases, the following additional TSPs are needed:
- Attribute Authorities.
Attributes Authorities provide users with attributes linked to public
key certificates.
An Arbitrator is an entity that arbitrates in disputes between a
signer and a verifier.
4.2. Signature Policies
The present document includes the concept of signature policies that
can be used to establish technical consistency when validating
electronic signatures.
When a comprehensive signature policy used by the verifier is either
explicitly indicated by the signer or implied by the data being
signed, then a consistent result can be obtained when validating an
electronic signature.
When the signature policy being used by the verifier is neither
indicated by the signer nor can be derived from other data, or the
signature policy is incomplete, then verifiers, including
arbitrators, may obtain different results when validating an
electronic signature. Therefore, comprehensive signature policies
that ensure consistency of signature validation are recommended from
both the signer's and verifier's point of view.
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Further information on signature policies is provided in:
- TR 102 038 [TR102038];
- Sections 5.8.1, C.1, and C.3.1 of the present document;
- RFC 3125 [RFC3125]; and
- TR 102 272 [TR102272].
4.3. Electronic Signature Formats
The current section provides an overview for two forms of CMS
advanced electronic signature specified in the present document,
namely, the CAdES Basic Electronic Signature (CAdES-BES) and the
CAdES Explicit Policy-based Electronic Signature (CAdES-EPES).
Conformance to the present document mandates that the signer create
one of these formats.
4.3.1. CAdES Basic Electronic Signature (CAdES-BES)
A CAdES Basic Electronic Signature (CAdES-BES), in accordance with
the present document, contains:
- The signed user data (e.g., the signer's document), as defined
in CMS (RFC 3852 [4]);
- A collection of mandatory signed attributes, as defined in CMS
(RFC 3852 [4]) and in ESS (RFC 2634 [5]);
- Additional mandatory signed attributes, defined in the present
document; and
- The digital signature value computed on the user data and, when
present, on the signed attributes, as defined in CMS (RFC 3852
[4]).
A CAdES Basic Electronic Signature (CAdES-BES), in accordance with
the present document, may contain:
- a collection of additional signed attributes; and
- a collection of optional unsigned attributes.
The mandatory signed attributes are:
- Content-type. It is defined in RFC 3852 [4] and specifies the
type of the EncapsulatedContentInfo value being signed. Details
are provided in Section 5.7.1 of the present document.
Rationale for its inclusion is provided in Annex C.3.7;
Pinkas, et al. Informational [Page 15]RFC 5126 CMS Advanced Electronic Signatures February 2008
- Message-digest. It is defined in RFC 3852 [4] and specifies the
message digest of the eContent OCTET STRING within
encapContentInfo being signed. Details are provided in Section
5.7.2;
- ESS signing-certificate OR ESS signing-certificate-v2. The ESS
signing-certificate attribute is defined in Enhanced Security
Services (ESS), RFC 2634 [5], and only allows for the use of
SHA-1 as a digest algorithm. The ESS signing-certificate-v2
attribute is defined in "ESS Update: Adding CertID Algorithm
Agility", RFC 5035 [15], and allows for the use of any digest
algorithm. A CAdES-BES claiming compliance with the present
document must include one of them. Section 5.7.3 provides the
details of these attributes. Rationale for its inclusion is
provided in Annex C.3.3.
Optional signed attributes may be added to the CAdES-BES, including
optional signed attributes defined in CMS (RFC 3852 [4]), ESS (RFC
2634 [5]), and the present document. Listed below are optional
attributes that are defined in Section 5 and have a rationale
provided in Annex C:
- Signing-time: as defined in CMS (RFC 3852 [4]), indicates the
time of the signature, as claimed by the signer. Details and
short rationale are provided in Section 5.9.1. Annex C.3.6
provides the rationale.
- content-hints: as defined in ESS (RFC 2634 [5]), provides
information that describes the innermost signed content of a
multi-layer message where one content is encapsulated in
another. Section 5.10.1 provides the specification details.
Annex C.3.8 provides the rationale.
- content-reference: as defined in ESS (RFC 2634 [5]), can be
incorporated as a way to link request and reply messages in an
exchange between two parties. Section 5.10.1 provides the
specification details. Annex C.3.9 provides the rationale.
- content-identifier: as defined in ESS (RFC 2634 [5]), contains
an identifier that may be used later on in the previous
content-reference attribute. Section 5.10.2 provides the
specification details.
- commitment-type-indication: this attribute is defined by the
present document as a way to indicate the commitment endorsed by
the signer when producing the signature. Section 5.11.1
provides the specification details. Annex C.3.2 provides the
rationale.
Pinkas, et al. Informational [Page 16]RFC 5126 CMS Advanced Electronic Signatures February 2008
- signer-location: this attribute is defined by the present
document. It allows the signer to indicate the place where the
signer purportedly produced the signature. Section 5.11.2
provides the specification details. Annex C.3.5 provides the
rationale.
- signer-attributes: this attribute is defined by the present
document. It allows a claimed or certified role to be
incorporated into the signed information. Section 5.11.3
provides the specification details. Annex C.3.4 provides the
rationale.
- content-time-stamp: this attribute is defined by the present
document. It allows a time-stamp token of the data to be signed
to be incorporated into the signed information. It provides
proof of the existence of the data before the signature was
created. Section 5.11.4 provides the specification details.
Annex C.3.6 provides the rationale.
A CAdES-BES form can also incorporate instances of unsigned
attributes, as defined in CMS (RFC 3852 [4]) and ESS (RFC 2634 [5]).
- CounterSignature, as defined in CMS (RFC 3852 [4]); it can be
incorporated wherever embedded signatures (i.e., a signature on
a previous signature) are needed. Section 5.9.2 provides the
specification details. Annex C.5 in Annex C provides the
rationale.
The structure of the CAdES-BES is illustrated in Figure 1.
+------Elect.Signature (CAdES-BES)------+
|+----------------------------------- + |
||+---------+ +----------+ | |
|||Signer's | | Signed | Digital | |
|||Document | |Attributes| Signature | |
||| | | | | |
||+---------+ +----------+ | |
|+------------------------------------+ |
+---------------------------------------+
Figure 1: Illustration of a CAdES-BES
The signer's conformance requirements of a CAdES-BES are defined in
Section 8.1.
Pinkas, et al. Informational [Page 17]RFC 5126 CMS Advanced Electronic Signatures February 2008
NOTE: The CAdES-BES is the minimum format for an electronic
signature to be generated by the signer. On its own, it does not
provide enough information for it to be verified in the longer
term. For example, revocation information issued by the relevant
certificate status information issuer needs to be available for
long-term validation (see Section 4.4.2).
The CAdES-BES satisfies the legal requirements for electronic
signatures, as defined in the European Directive on Electronic
Signatures, (see Annex C for further discussion on the relationship
of the present document to the Directive). It provides basic
authentication and integrity protection.
The semantics of the signed data of a CAdES-BES or its context may
implicitly indicate a signature policy to the verifier.
Specification of the contents of signature policies is outside the
scope of the present document. However, further information on
signature policies is provided in TR 102 038 [TR102038], RFC 3125
[RFC3125], and Sections 5.8.1, C.1, and C.3.1 of the present
document.
4.3.2. CAdES Explicit Policy-based Electronic Signatures (CAdES-EPES)
A CAdES Explicit Policy-based Electronic Signature (CAdES-EPES), in
accordance with the present document, extends the definition of an
electronic signature to conform to the identified signature policy.
A CAdES Explicit Policy-based Electronic Signature (CAdES-EPES)
incorporates a signed attribute (sigPolicyID attribute) indicating
the signature policy that shall be used to validate the electronic
signature. This signed attribute is protected by the signature. The
signature may also have other signed attributes required to conform
to the mandated signature policy.
Section 5.7.3 provides the details on the specification of
signature-policy-identifier attribute. Annex C.1 provides a short
rationale. Specification of the contents of signature policies is
outside the scope of the present document.
Further information on signature policies is provided in TR 102 038
[TR102038] and Sections 5.8.1, C.1, and C.3.1 of the present
document.
Pinkas, et al. Informational [Page 18]RFC 5126 CMS Advanced Electronic Signatures February 2008
The structure of the CAdES-EPES is illustrated in Figure 2.
+------------- Elect.Signature (CAdES-EPES) ---------------+
| |
|+-------------------------------------------------------+ |
|| +-----------+ | |
|| | | +---------------------------+ | |
|| | | | +----------+ | | |
|| | Signer's | | |Signature | Signed | Digital | |
|| | Document | | |Policy ID | Attributes |Signature| |
|| | | | +----------+ | | |
|| | | +---------------------------+ | |
|| +-----------+ | |
|+-------------------------------------------------------+ |
| |
+----------------------------------------------------------+
Figure 2: Illustration of a CAdES-EPES
The signer's conformance requirements of CAdES-EPES are defined in
Section 8.2.
4.4. Electronic Signature Formats with Validation Data
Validation of an electronic signature, in accordance with the present
document, requires additional data needed to validate the electronic
signature. This additional data is called validation data, and
includes:
- Public Key Certificates (PKCs);
- revocation status information for each PKC;
- trusted time-stamps applied to the digital signature, otherwise
a time-mark shall be available in an audit log.
- when appropriate, the details of a signature policy to be used
to verify the electronic signature.
The validation data may be collected by the signer and/or the
verifier. When the signature-policy-identifier signed attribute is
present, it shall meet the requirements of the signature policy.
Pinkas, et al. Informational [Page 19]RFC 5126 CMS Advanced Electronic Signatures February 2008
Validation data includes CA certificates as well as revocation status
information in the form of Certificate Revocation Lists (CRLs) or
certificate status information (OCSP) provided by an online service.
Validation data also includes evidence that the signature was created
before a particular point in time; this may be either a time-stamp
token or time-mark.
The present document defines unsigned attributes able to contain
validation data that can be added to CAdES-BES and CAdES-EPES,
leading to electronic signature formats that include validation data.
The sections below summarize these formats and their most relevant
characteristics.
4.4.1. Electronic Signature with Time (CAdES-T)
An electronic signature with time (CAdES-T), in accordance with the
present document, is when there exits trusted time associated with
the ES.
The trusted time may be provided by:
- a time-stamp attribute as an unsigned attribute added to the ES;
and
- a time-mark of the ES provided by a Trusted Service Provider.
The time-stamp attribute contains a time-stamp token of the
electronic signature value. Section 6.1.1 provides the specification
details. Annex C.4.3 provides the rationale.
A time-mark provided by a Trusted Service would have a similar effect
to the signature-time-stamp attribute, but in this case, no attribute
is added to the ES, as it is the responsibility of the TSP to provide
evidence of a time-mark when required to do so. The management of
time marks is outside the scope of the present document.
Trusted time provides the initial steps towards providing long-term
validity. Electronic signatures with the time-stamp attribute or a
time-marked BES/EPES, forming the CAdES-T are illustrated in Figure
3.
Pinkas, et al. Informational [Page 20]RFC 5126 CMS Advanced Electronic Signatures February 2008
+-------------------------------------------------CAdES-T ---------+
|+------ CAdES-BES or CAdES-EPES -------+ |
||+-----------------------------------+ | +----------------------+ |
|||+---------+ +----------+ | | | | |
||||Signer's | | Signed | Digital | | | Signature-time-stamp | |
||||Document | |Attributes| Signature | | | attribute required | |
|||| | | | | | | when using time | |
|||+---------+ +----------+ | | | stamps. | |
||+-----------------------------------+ | | | |
|+--------------------------------------+ | or the BES/EPES | |
| | shall be time-marked | |
| | | |
| | Management and | |
| | provision of time | |
| | mark is the | |
| | responsibility of | |
| | the TSP. | |
| +----------------------+ |
+------------------------------------------------------------------+
Figure 3: Illustration of CAdES-T formats
NOTE 1: A time-stamp token is added to the CAdES-BES or CAdES-EPES
as an unsigned attribute.
NOTE 2: Time-stamp tokens that may themselves include unsigned
attributes required to validate the time-stamp token, such as the
complete-certificate-references and complete-revocation-references
attributes, as defined by the present document.
4.4.2. ES with Complete Validation Data References (CAdES-C)
Electronic Signature with Complete validation data references
(CAdES-C), in accordance with the present document, adds to the
CAdES-T the complete-certificate-references and
complete-revocation-references attributes, as defined by the present
document. The complete-certificate-references attribute contains
references to all the certificates present in the certification path
used for verifying the signature. The complete-revocation-references
attribute contains references to the CRLs and/or OCSPs responses used
for verifying the signature. Section 6.2 provides the specification
details. Storing the references allows the values of the
certification path and the CRLs or OCSPs responses to be stored
elsewhere, reducing the size of a stored electronic signature format.
Pinkas, et al. Informational [Page 21]RFC 5126 CMS Advanced Electronic Signatures February 2008
Sections C.4.1 to C.4.2 provide rationale on the usage of validation
data and when it is suitable to generate the CAdES-C form.
Electronic signatures, with the additional validation data forming
the CAdES-C, are illustrated in Figure 4.
+------------------------- CAdES-C --------------------------------+
|+----------------------------- CAdES-T ---------+ |
|| +----------+ | +-------------+ |
|| |Timestamp | | | | |
|| |attribute | | | | |
||+- CAdES-BES or CAdES-EPES ------+|over | | | | |
||| ||digital | | | Complete | |
|||+---------++----------+ ||signature | | | certificate | |
||||Signer's || Signed | Digital ||is | | | and | |
||||Document ||Attributes|Signature||mandatory | | | revocation | |
|||| || | ||if is not | | | references | |
|||+---------++----------+ ||timemarked| | | | |
||+--------------------------------++----------+ | | | |
|+-----------------------------------------------+ +-------------+ |
+------------------------------------------------------------------+
Figure 4: Illustration of CAdES-C format
NOTE 1: The complete certificate and revocation references are
added to the CAdES-T as an unsigned attribute.
NOTE 2: As a minimum, the signer will provide the CAdES-BES or,
when indicating that the signature conforms to an explicit signing
policy, the CAdES-EPES.
NOTE 3: To reduce the risk of repudiating signature creation, the
trusted time indication needs to be as close as possible to the
time the signature was created. The signer or a TSP could provide
the CAdES-T; if not, the verifier should create the CAdES-T on
first receipt of an electronic signature because the CAdES-T
provides independent evidence of the existence of the signature
prior to the trusted time indication.
NOTE 4: A CAdES-T trusted time indication must be created before a
certificate has been revoked or expired.
NOTE 5: The signer and TSP could provide the CAdES-C to minimize
this risk, and when the signer does not provide the CAdES-C, the
verifier should create the CAdES-C when the required component of
revocation and validation data become available; this may require
a grace period.
Pinkas, et al. Informational [Page 22]RFC 5126 CMS Advanced Electronic Signatures February 2008
NOTE 6: A grace period permits certificate revocation information
to propagate through the revocation processes. This period could
extend from the time an authorized entity requests certificate
revocation to when the information is available for the relying
party to use. In order to make sure that the certificate was not
revoked at the time the signature was time-marked or time-stamped,
verifiers should wait until the end of the grace period. A
signature policy may define specific values for grace periods.
An illustration of a grace period is provided in Figure 5.
+<--------------Grace Period --------->+
----+-------+-------+--------+---------------------+----------+
^ ^ ^ ^ ^ ^
| | | | | |
| | | | | |
Signature | First | Second |
creation | revocation | revocation |
time | status | status |
| checking | checking |
| | |
Time-stamp Certification Build
or path CAdES-C
time-mark construction
over & verification
signature
Figure 5: Illustration of a grace period
NOTE 7: CWA 14171 [CWA14171] specifies a signature validation
process using CAdES-T, CAdES-C, and a grace period. Annex B
provides example validation processes. Annex C.4 provides
additional information about applying grace periods during the
validation process.
The verifier's conformance requirements are defined in Section 8.3
for time-stamped CAdES-C, and Section 8.4 for time-marked CAdES-C.
The present document only defines conformance requirements for the
verifier up to an ES with Complete validation data (CAdES-C). This
means that none of the extended and archive forms of electronic
signatures, as defined in Sections 4.4.3 to 4.4.4, need to be
implemented to achieve conformance to the present document.
4.4.3. Extended Electronic Signature Formats
CAdES-C can be extended by adding unsigned attributes to the
electronic signature. The present document defines various unsigned
attributes that are applicable for very long-term verification, and
Pinkas, et al. Informational [Page 23]RFC 5126 CMS Advanced Electronic Signatures February 2008
for preventing some disaster situations that are discussed in Annex
C. Annex B provides the details of the various extended formats, all
the required unsigned attributes for each type, and how they can be
used within the electronic signature validation process. The
sections below give an overview of the various forms of extended
signature formats in the present document.
4.4.3.1. EXtended Long Electronic Signature (CAdES-X Long)
Extended Long format (CAdES-X Long), in accordance with the present
document, adds the certificate-values and revocation-values
attributes to the CAdES-C format. The first one contains the whole
certificate path required for verifying the signature; the second one
contains the CRLs and/OCSP responses required for the validation of
the signature. This provides a known repository of certificate and
revocation information required to validate a CAdES-C and prevents
such information from getting lost. Sections 6.3.3 and 6.3.4 give
specification details. Annex B.1.1 gives details on the production
of the format. Annexes C4.1 to C.4.2 provide the rationale.
The structure of the CAdES-X Long format is illustrated in Figure 6.
+----------------------- CAdES-X-Long -----------------------------+
|+------------------------------------ CadES-C --+ |
|| +----------+ | +-------------+ |
||+------ CAdES -------------------+|Timestamp | | | | |
||| || over | | | Complete | |
|||+---------++----------+ ||digital | | | certificate | |
||||Signer's || Signed | Digital ||signature | | | and | |
||||Document ||Attributes|Signature|| | | | revocation | |
|||| || | ||Optional | | | data | |
|||+---------++----------+ ||when | | | | |
||+--------------------------------+|timemarked| | | | |
|| +----------+ | | | |
|| +-------------+ | +-------------+ |
|| | Complete | | |
|| | certificate | | |
|| | and | | |
|| | revocation | | |
|| | references | | |
|| +-------------+ | |
|+-----------------------------------------------+ |
| |
+------------------------------------------------------------------+
Figure 6: Illustration of CAdES-X-Long
Pinkas, et al. Informational [Page 24]RFC 5126 CMS Advanced Electronic Signatures February 2008
4.4.3.2. EXtended Electronic Signature with Time Type 1
(CAdES-X Type 1)
Extended format with time type 1 (CAdES-X Type 1), in accordance with
the present document, adds the CAdES-C-time-stamp attribute, whose
content is a time-stamp token on the CAdES-C itself, to the CAdES-C
format.
This provides an integrity and trusted time protection over all the
elements and references. It may protect the certificates, CRLs, and
OCSP responses in case of a later compromise of a CA key, CRL key, or
OCSP issuer key. Section 6.3.5 provides the specification details.
Annex B.1.2 gives details on the production of the time-stamping
process. Annex C.4.4.1 provides the rationale.
The structure of the CAdES-X Type 1 format is illustrated in Figure
7.
+----------------------- CAdES-X-Type 1 ------------------------------+
|+-------------------------------------- CAdES-C -----+ |
|| +-------------+ | +-----------+ |
||+--------- CAdES ------------------+| Timestamp | | | | |
||| || over | | | | |
|||+---------++----------+ || digital | | | | |
||||Signer's || Signed | Digital || signature | | | Timestamp | |
||||Document ||Attributes| Signature || | | | over | |
|||| || | || Optional | | | CAdES-C | |
|||+---------++----------+ || when | | | | |
||+----------------------------------+| time-marked | | | | |
|| +-------------+ | | | |
|| +-------------+ | +-----------+ |
|| | Complete | | |
|| | certificate | | |
|| | and | | |
|| | revocation | | |
|| | references | | |
|| +-------------+ | |
|+----------------------------------------------------+ |
+---------------------------------------------------------------------+
Figure 7: Illustration of CAdES-X Type 1
Pinkas, et al. Informational [Page 25]RFC 5126 CMS Advanced Electronic Signatures February 2008
4.4.3.3. EXtended Electronic Signature with Time Type 2
(CAdES-X Type 2)
Extended format with time type 2 (CAdES-X Type 2), in accordance with
the present document, adds to the CAdES-C format the
CAdES-C-time-stamped-certs-crls-references attribute, whose content
is a time-stamp token on the certification path and revocation
information references. This provides an integrity and trusted time
protection over all the references.
It may protect the certificates, CRLs and OCSP responses in case of a
later compromise of a CA key, CRL key or OCSP issuer key.
Both CAdES-X Type 1 and CAdES-X Type 2 counter the same threats, and
the usage of one or the other depends on the environment. Section
6.3.5 provides the specification details. Annex B.1.3 gives details
on the production of the time-stamping process. Annex C.4.4.2
provides the rationale.
The structure of the CAdES-X Type 2 format is illustrated in Figure
8.
+------------------------- CAdES-X-Type 2 ----------------------------+
|+----------------------------------------CAdES-C ---+ |
|| +------------+| |
||+----- CAdES -----------------------+| Timestamp || |
||| || over || |
|||+---------+ +----------+ || digital || +-------------+|
||||Signer's | | Signed | Digital || signature || | Time-stamp ||
||||Document | |Attributes| signature || || | only over ||
|||| | | | || optional || | complete ||
|||+---------+ +----------+ || when || | certificate ||
||+-----------------------------------+| timemarked || | and ||
|| +------------+| | revocation ||
|| +-------------+ | | references ||
|| | Complete | | +-------------+|
|| | certificate | | |
|| | and | | |
|| | revocation | | |
|| | references | | |
|| +-------------+ | |
|+---------------------------------------------------+ |
+---------------------------------------------------------------------+
Figure 8: Illustration of CAdES-X Type 2
Pinkas, et al. Informational [Page 26]RFC 5126 CMS Advanced Electronic Signatures February 2008
4.4.3.4. EXtended Long Electronic Signature with Time (CAdES-X Long
Type 1 or 2)
Extended Long with Time (CAdES-X Long Type 1 or 2), in accordance
with the present document, is a combination of CAdES-X Long and one
of the two former types (CAdES-X Type 1 and CAdES-X Type 2). Annex
B.1.4 gives details on the production of the time-stamping process.
Annex C.4.8 in Annex C provides the rationale.
The structure of the CAdES-X Long Type 1 and CAdES-X Long Type 2
format is illustrated in Figure 9.
+------------------ CAdES-X Long Type 1 or 2 -----------------------+
| +--------------+|
|+-------------------------------------- CAdES-C --+|+------------+||
|| ||| Timestamp |||
||+------- CAdES --------------------++----------+ ||| over |||
||| ||Timestamp | ||| CAdES-C |||
||| ||over | ||+------------+||
|||+---------++----------+ ||digital | || OR ||
||||Signer's || Signed | Digital ||signature | ||+------------+||
||||Document ||Attributes| signature || | ||| Timestamp |||
|||| || | ||Optional | ||| only over |||
|||+---------++----------+ ||when | ||| complete |||
||+----------------------------------+|timemarked| ||| certificate|||
|| +----------+ ||| and |||
|| ||| Revocation |||
|| +-------------+ ||| References |||
|| | Complete | ||+------------+||
|| | certificate | |+--------------+|
|| | and | | +------------+ |
|| | revocation | | | Complete | |
|| | references | | |certificate | |
|| +-------------+ | | and | |
|+-------------------------------------------------+ |revocation | |
| | value | |
| +------------+ |
+-------------------------------------------------------------------+
Figure 9: Illustration of CAdES-X Long Type 1 and CAdES Long Type 2
4.4.4. Archival Electronic Signature (CAdES-A)
Archival Form (CAdES-A), in accordance with the present document,
builds on a CAdES-X Long or a CAdES-X Long Type 1 or 2 by adding one
or more archive-time-stamp attributes. This form is used for
archival of long-term signatures. Successive time-stamps protect the
whole material against vulnerable hashing algorithms or the breaking
Pinkas, et al. Informational [Page 27]RFC 5126 CMS Advanced Electronic Signatures February 2008
of the cryptographic material or algorithms. Section 6.4 contains
the specification details. Sections C.4.5 and C.4.8 provide the
rationale.
The structure of the CAdES-A form is illustrated in Figure 10.
+---------------------------CAdES-A ---------------------------------+
|+----------------------------------------------------+ |
|| +--------------+| +----------+ |
||+----------------------CAdES-C ----+|+------------+|| | | |
||| +----------+ ||| Timestamp ||| | | |
|||+---- CAdES-BES ----+|Timestamp | ||| over ||| | | |
|||| or CAdeS-EPES || over | ||| CAdES-C ||| | Archive | |
|||| ||digital | ||+------------+|| | | |
|||| ||signature | || or || |Timestamp | |
|||| || | ||+------------+|| | | |
|||| ||Optional | ||| Timestamp ||| | | |
|||| ||when | ||| only over ||| | | |
|||| ||Timemarked| ||| complete ||| | | |
|||+-------------------+| | ||| certificate||| +----------+ |
||| +----------+ ||| and ||| |
||| +-------------+ ||| revocation ||| |
||| | Complete | ||| references ||| |
||| | certificate | ||+------------+|| |
||| | and | |+--------------+| |
||| | revocation | | +------------+ | |
||| | references | | | Complete | | |
||| +-------------+ | |certificate | | |
||| | | and | | |
||+----------------------------------+ |revocation | | |
|| | values | | |
|| +------------+ | |
|+----------------------------------------------------+ |
+--------------------------------------------------------------------+
Figure 10: Illustration of CAdES-A
4.5. Arbitration
The CAdES-C may be used for arbitration should there be a dispute
between the signer and verifier, provided that:
- the arbitrator knows where to retrieve the signer's certificate
(if not already present), all the cross-certificates and the
required CRLs, ACRLs, or OCSP responses referenced in the
CAdES-C;
Pinkas, et al. Informational [Page 28]RFC 5126 CMS Advanced Electronic Signatures February 2008
- when time-stamping in the CAdES-T is being used, the certificate
from the TSU that has issued the time-stamp token in the CAdES-T
format is still within its validity period;
- when time-stamping in the CAdES-T is being used, the certificate
from the TSU that has issued the time-stamp token in the CAdES-T
format is not revoked at the time of arbitration;
- when time-marking in the CAdES-T is being used, a reliable audit
trail from the Time-Marking Authority is available for
examination regarding the time;
- none of the private keys corresponding to the certificates used
to verify the signature chain have ever been compromised;
- the cryptography used at the time the CAdES-C was built has not
been broken at the time the arbitration is performed; and
- if the signature policy can be explicitly or implicitly
identified, then an arbitrator is able to determine the rules
required to validate the electronic signature.
4.6. Validation Process
The validation process validates an electronic signature; the output
status of the validation process can be:
- invalid;
- incomplete validation; or
- valid.
An invalid response indicates that either the signature format is
incorrect or that the digital signature value fails verification
(e.g., the integrity check on the digital signature value fails, or
any of the certificates on which the digital signature verification
depends is known to be invalid or revoked).
An incomplete validation response indicates that the signature
validation status is currently unknown. In the case of incomplete
validation, additional information may be made available to the
application or user, thus allowing them to decide what to do with the
electronic signature. In the case of incomplete validation, the
electronic signature may be checked again at some later time when
additional information becomes available.
Pinkas, et al. Informational [Page 29]RFC 5126 CMS Advanced Electronic Signatures February 2008
NOTE: For example, an incomplete validation may be because all the
required certificates are not available or the grace period is not
completed.
A valid response indicates that the signature has passed
verification, and it complies with the signature validation policy.
Example validation sequences are illustrated in Annex B.
5. Electronic Signature Attributes
This section builds upon the existing Cryptographic Message Syntax
(CMS), as defined in RFC 3852 [4], and Enhanced Security Services
(ESS), as defined in RFC 2634 [5]. The overall structure of an
Electronic Signature is as defined in CMS. The Electronic Signature
(ES) uses attributes defined in CMS, ESS, and the present document.
The present document defines ES attributes that it uses and that are
not defined elsewhere.
The mandated set of attributes and the digital signature value is
defined as the minimum Electronic Signature (ES) required by the
present document. A signature policy may mandate that other signed
attributes be present.
5.1. General Syntax
The general syntax of the ES is as defined in CMS (RFC 3852 [4]).
NOTE: CMS defines content types for id-data, id-signedData,
id-envelopedData, id-digestedData, id-encryptedData, and
id-authenticatedData. Although CMS permits other documents to
define other content types, the ASN.1 type defined should not be a
CHOICE type. The present document does not define other content
types.
5.2. Data Content Type
The data content type of the ES is as defined in CMS (RFC 3852 [4]).
NOTE: If the content type is id-data, it is recommended that the
content be encoded using MIME, and that the MIME type is used to
identify the presentation format of the data. See Annex F.1 for
an example of using MIME to identify the encoding type.
5.3. Signed-data Content Type
The Signed-data content type of the ES is as defined in CMS (RFC 3852
[4]).
Pinkas, et al. Informational [Page 30]RFC 5126 CMS Advanced Electronic Signatures February 2008
5.4. SignedData Type
The syntax of the SignedData of the ES is as defined in CMS (RFC 3852
[4]).
The fields of type SignedData are as defined in CMS (RFC 3852 [4]).
The identification of a signer's certificate used to create the
signature is always signed (see Section 5.7.3). The validation
policy may specify requirements for the presence of certain
certificates. The degenerate case, where there are no signers, is
not valid in the present document.
5.5. EncapsulatedContentInfo Type
The syntax of the EncapsulatedContentInfo type ES is as defined in
CMS (RFC 3852 [4]).
For the purpose of long-term validation, as defined by the present
document, it is advisable that either the eContent is present, or the
data that is signed is archived in such as way as to preserve any
data encoding. It is important that the OCTET STRING used to
generate the signature remains the same every time either the
verifier or an arbitrator validates the signature.
NOTE: The eContent is optional in CMS :
- When it is present, this allows the signed data to be
encapsulated in the SignedData structure, which then
contains both the signed data and the signature. However,
the signed data may only be accessed by a verifier able to
decode the ASN.1 encoded SignedData structure.
- When it is missing, this allows the signed data to be sent
or stored separately from the signature, and the SignedData
structure only contains the signature. It is, in the case
of the signature, only the data that is signed that needs to
be stored and distributed in such as way as to preserve any
data encoding.
The degenerate case where there are no signers is not valid in the
present document.
5.6. SignerInfo Type
The syntax of the SignerInfo type ES is as defined in CMS (RFC 3852
[4]).
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Per-signer information is represented in the type SignerInfo. In the
case of multiple independent signatures (see Annex B.5), there is an
instance of this field for each signer.
The fields of type SignerInfo have the meanings defined in CMS (RFC
3852 [4]), but the signedAttrs field shall contain the following
attributes:
- content-type, as defined in Section 5.7.1; and
- message-digest, as defined in Section 5.7.2;
- signing-certificate, as defined in Section 5.7.3.
5.6.1. Message Digest Calculation Process
The message digest calculation process is as defined in CMS (RFC 3852
[4]).
5.6.2. Message Signature Generation Process
The input to the message signature generation process is as defined
in CMS (RFC 3852 [4]).
5.6.3. Message Signature Verification Process
The procedures for message signature verification are defined in CMS
(RFC 3852 [4]) and enhanced in the present document: the input to the
signature verification process must be the signer's public key, which
shall be verified as correct using the signing certificate reference
attribute containing a reference to the signing certificate, i.e.,
when SigningCertificateV2 from RFC 5035 [16] or SigningCertificate
from ESS [5] is used, the public key from the first certificate
identified in the sequence of certificate identifiers from
SigningCertificate must be the key used to verify the digital
signature.
5.7. Basic ES Mandatory Present Attributes
The following attributes shall be present with the signed-data
defined by the present document. The attributes are defined in CMS
(RFC 3852 [4]).
5.7.1. content-type
The content-type attribute indicates the type of the signed content.
The syntax of the content-type attribute type is as defined in CMS
(RFC 3852 [4]) Section 11.1.
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NOTE 1: As stated in RFC 3852 [4] , the content-type attribute
must have its value (i.e., ContentType) equal to the eContentType
of the EncapsulatedContentInfo value being signed.
NOTE 2: For implementations supporting signature generation, if
the content-type attribute is id-data, then it is recommended that
the eContent be encoded using MIME. For implementations
supporting signature verification, if the signed data (i.e.,
eContent) is MIME-encoded, then the OID of the content-type
attribute must be id-data. In both cases, the MIME
content-type(s) must be used to identify the presentation format
of the data. See Annex F for further details about the use of
MIME.
5.7.2. Message Digest
The syntax of the message-digest attribute type of the ES is as
defined in CMS (RFC 3852 [4]).
5.7.3. Signing Certificate Reference Attributes
The Signing certificate reference attributes are supported by using
either the ESS signing-certificate attribute or the
ESS-signing-certificate-v2 attribute.
These attributes shall contain a reference to the signer's
certificate; they are designed to prevent simple substitution and
reissue attacks and to allow for a restricted set of certificates to
be used in verifying a signature. They have a compact form (much
shorter than the full certificate) that allows for a certificate to
be unambiguously identified.
One, and only one, of the following alternative attributes shall be
present with the signedData, defined by the present document:
- The ESS signing-certificate attribute, defined in ESS [5], must
be used if the SHA-1 hashing algorithm is used.
- The ESS signing-certificate-v2 attribute, defined in "ESS
Update: Adding CertID Algorithm Agility", RFC 5035 [15], which
shall be used when other hashing algorithms are to be used.
The certificate to be used to verify the signature shall be
identified in the sequence (i.e., the certificate from the signer),
and the sequence shall not be empty. The signature validation policy
may mandate other certificates be present that may include all the
certificates up to the trust anchor.
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5.7.3.1. ESS signing-certificate Attribute Definition
The syntax of the signing-certificate attribute type of the ES is as
defined in Enhanced Security Services (ESS), RFC 2634 [5], and
further qualified in the present document.
The sequence of the policy information field is not used in the
present document.
The ESS signing-certificate attribute shall be a signed attribute.
The encoding of the ESSCertID for this certificate shall include the
issuerSerial field.
If present, the issuerAndSerialNumber in SignerIdentifier field of
the SignerInfo shall match the issuerSerial field present in
ESSCertID. In addition, the certHash from ESSCertID shall match the
SHA-1 hash of the certificate. The certificate identified shall be
used during the signature verification process. If the hash of the
certificate does not match the certificate used to verify the
signature, the signature shall be considered invalid.
NOTE: Where an attribute certificate is used by the signer to
associate a role, or other attributes of the signer, with the
electronic signature; this is placed in the signer-attributes
attribute as defined in Section 5.8.3.
5.7.3.2. ESS signing-certificate-v2 Attribute Definition
The ESS signing-certificate-v2 attribute is similar to the ESS
signing-certificate defined above, except that this attribute can be
used with hashing algorithms other than SHA-1.
The syntax of the signing-certificate-v2 attribute type of the ES is
as defined in "ESS Update: Adding CertID Algorithm Agility", RFC 5035
[15], and further qualified in the present document.
The sequence of the policy information field is not used in the
present document.
This attribute shall be used in the same manner as defined above for
the ESS signing-certificate attribute.
The object identifier for this attribute is:
id-aa-signingCertificateV2 OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 47 }
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If present, the issuerAndSerialNumber in SignerIdentifier field of
the SignerInfo shall match the issuerSerial field present in
ESSCertIDv2. In addition, the certHash from ESSCertIDv2 shall match
the hash of the certificate computed using the hash function
specified in the hashAlgorithm field. The certificate identified
shall be used during the signature verification process. If the hash
of the certificate does not match the certificate used to verify the
signature, the signature shall be considered invalid.
NOTE 1: Where an attribute certificate is used by the signer to
associate a role, or other attributes of the signer, with the
electronic signature; this is placed in the signer-attributes
attribute as defined in Section 5.8.3.
NOTE 2: RFC 3126 was using the other signing-certificate attribute
(see Section 5.7.3.3) for the same purpose. Its use is now
deprecated, since this structure is simpler.
5.7.3.3. Other signing-certificate Attribute Definition
RFC 3126 was using the other signing-certificate attribute as an
alternative to the ESS signing-certificate when hashing algorithms
other than SHA-1 were being used. Its use is now deprecated, since
the structure of the signing-certificate-v2 attribute is simpler.
Its description is however still present in this version for
backwards compatibility.
id-aa-ets-otherSigCert OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 19 }
The other-signing-certificate attribute value has the ASN.1 syntax
OtherSigningCertificate:
OtherSigningCertificate ::= SEQUENCE {
certs SEQUENCE OF OtherCertID,
policies SEQUENCE OF PolicyInformation OPTIONAL
-- NOT USED IN THE PRESENT DOCUMENT }
OtherCertID ::= SEQUENCE {
otherCertHash OtherHash,
issuerSerial IssuerSerial OPTIONAL }
OtherHash ::= CHOICE {
sha1Hash OtherHashValue, -- This contains a SHA-1 hash
otherHash OtherHashAlgAndValue}
OtherHashValue ::= OCTET STRING
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OtherHashAlgAndValue ::= SEQUENCE {
hashAlgorithm AlgorithmIdentifier,
hashValue OtherHashValue }
5.8. Additional Mandatory Attributes for Explicit Policy-based
Electronic Signatures
5.8.1. signature-policy-identifier
The present document mandates that for CAdES-EPES, a reference to the
signature policy is included in the signedData. This reference is
explicitly identified. A signature policy defines the rules for
creation and validation of an electronic signature, and is included
as a signed attribute with every Explicit Policy-based Electronic
Signature. The signature-policy-identifier shall be a signed
attribute.
The following object identifier identifies the
signature-policy-identifier attribute:
id-aa-ets-sigPolicyId OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 15 }
signature-policy-identifier attribute values have ASN.1 type
SignaturePolicyIdentifier:
SignaturePolicyIdentifier ::= CHOICE {
signaturePolicyId SignaturePolicyId,
signaturePolicyImplied SignaturePolicyImplied
-- not used in this version
}
SignaturePolicyId ::= SEQUENCE {
sigPolicyId SigPolicyId,
sigPolicyHash SigPolicyHash,
sigPolicyQualifiers SEQUENCE SIZE (1..MAX) OF
SigPolicyQualifierInfo OPTIONAL}
SignaturePolicyImplied ::= NULL
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The sigPolicyId field contains an object-identifier that uniquely
identifies a specific version of the signature policy. The syntax of
this field is as follows:
SigPolicyId ::= OBJECT IDENTIFIER
The sigPolicyHash field optionally contains the identifier of the
hash algorithm and the hash of the value of the signature policy.
The hashValue within the sigPolicyHash may be set to zero to indicate
that the policy hash value is not known.
NOTE: The use of a zero sigPolicyHash value is to ensure backwards
compatibility with earlier versions of the current document. If
sigPolicyHash is zero, then the hash value should not be checked
against the calculated hash value of the signature policy.
If the signature policy is defined using ASN.1, then the hash is
calculated on the value without the outer type and length fields, and
the hashing algorithm shall be as specified in the field
sigPolicyHash.
If the signature policy is defined using another structure, the type
of structure and the hashing algorithm shall be either specified as
part of the signature policy, or indicated using a signature policy
qualifier.
SigPolicyHash ::= OtherHashAlgAndValue
OtherHashAlgAndValue ::= SEQUENCE {
hashAlgorithm AlgorithmIdentifier,
hashValue OtherHashValue }
OtherHashValue ::= OCTET STRING
A Signature Policy Identifier may be qualified with other information
about the qualifier. The semantics and syntax of the qualifier is as
associated with the object-identifier in the sigPolicyQualifierId
field. The general syntax of this qualifier is as follows:
SigPolicyQualifierInfo ::= SEQUENCE {
sigPolicyQualifierId SigPolicyQualifierId,
sigQualifier ANY DEFINED BY sigPolicyQualifierId }
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The present document specifies the following qualifiers:
- spuri: this contains the web URI or URL reference to the
signature policy, and
- sp-user-notice: this contains a user notice that should be
displayed whenever the signature is validated.
sigpolicyQualifierIds defined in the present document:
SigPolicyQualifierId ::= OBJECT IDENTIFIER
id-spq-ets-uri OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-spq(5) 1 }
SPuri ::= IA5String
id-spq-ets-unotice OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-spq(5) 2 }
SPUserNotice ::= SEQUENCE {
noticeRef NoticeReference OPTIONAL,
explicitText DisplayText OPTIONAL}
NoticeReference ::= SEQUENCE {
organization DisplayText,
noticeNumbers SEQUENCE OF INTEGER }
DisplayText ::= CHOICE {
visibleString VisibleString (SIZE (1..200)),
bmpString BMPString (SIZE (1..200)),
utf8String UTF8String (SIZE (1..200)) }
5.9. CMS Imported Optional Attributes
The following attributes may be present with the signed-data; the
attributes are defined in CMS (RFC 3852 [4]) and are imported into
the present document. Where appropriate, the attributes are
qualified and profiled by the present document.
5.9.1. signing-time
The signing-time attribute specifies the time at which the signer
claims to have performed the signing process.
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Signing-time attribute values for ES have the ASN.1 type SigningTime
as defined in CMS (RFC 3852 [4]).
NOTE: RFC 3852 [4] states that dates between January 1, 1950 and
December 31, 2049 (inclusive) must be encoded as UTCTime. Any
dates with year values before 1950 or after 2049 must be encoded
as GeneralizedTime.
5.9.2. countersignature
The countersignature attribute values for ES have ASN.1 type
CounterSignature, as defined in CMS (RFC 3852 [4]). A
countersignature attribute shall be an unsigned attribute.
5.10. ESS-Imported Optional Attributes
The following attributes may be present with the signed-data defined
by the present document. The attributes are defined in ESS and are
imported into the present document and are appropriately qualified
and profiled by the present document.
5.10.1. content-reference Attribute
The content-reference attribute is a link from one SignedData to
another. It may be used to link a reply to the original message to
which it refers, or to incorporate by reference one SignedData into
another. The content-reference attribute shall be a signed
attribute.
content-reference attribute values for ES have ASN.1 type
ContentReference, as defined in ESS (RFC 2634 [5]).
The content-reference attribute shall be used as defined in ESS (RFC
2634 [5]).
5.10.2. content-identifier Attribute
The content-identifier attribute provides an identifier for the
signed content, for use when a reference may be later required to
that content; for example, in the content-reference attribute in
other signed data sent later. The content-identifier shall be a
signed attribute.
content-identifier attribute type values for the ES have an ASN.1
type ContentIdentifier, as defined in ESS (RFC 2634 [5]).
The minimal content-identifier attribute should contain a
concatenation of user-specific identification information (such as a
Pinkas, et al. Informational [Page 39]RFC 5126 CMS Advanced Electronic Signatures February 2008
user name or public keying material identification information), a
GeneralizedTime string, and a random number.
5.10.3. content-hints Attribute
The content-hints attribute provides information on the innermost
signed content of a multi-layer message where one content is
encapsulated in another.
The syntax of the content-hints attribute type of the ES is as
defined in ESS (RFC 2634 [5]).
When used to indicate the precise format of the data to be presented
to the user, the following rules apply:
- the contentType indicates the type of the associated content.
It is an object identifier (i.e., a unique string of integers)
assigned by an authority that defines the content type; and
- when the contentType is id-data, the contentDescription shall
define the presentation format; the format may be defined by
MIME types.
When the format of the content is defined by MIME types, the
following rules apply:
- the contentType shall be id-data, as defined in CMS (RFC 3852
[4]);
- the contentDescription shall be used to indicate the encoding of
the data, in accordance with the rules defined RFC 2045 [6]; see
Annex F for an example of structured contents and MIME.
NOTE 1: id-data OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
rsadsi(113549) pkcs(1) pkcs7(7) 1 }
NOTE 2: contentDescription is optional in ESS (RFC 2634 [5]). It may
be used to complement contentTypes defined elsewhere; such
definitions are outside the scope of the present document.
5.11. Additional Optional Attributes Defined in the Present Document
This section defines a number of attributes that may be used to
indicate additional information to a verifier:
a) the type of commitment from the signer, and/or
b) the claimed location where the signature is performed, and/or
Pinkas, et al. Informational [Page 40]RFC 5126 CMS Advanced Electronic Signatures February 2008
c) claimed attributes or certified attributes of the signer,
and/or
d) a content time-stamp applied before the content was signed.
5.11.1. commitment-type-indication Attribute
There may be situations where a signer wants to explicitly indicate
to a verifier that by signing the data, it illustrates a type of
commitment on behalf of the signer. The commitment-type-indication
attribute conveys such information.
The commitment-type-indication attribute shall be a signed attribute.
The commitment type may be:
- defined as part of the signature policy, in which case, the
commitment type has precise semantics that are defined as part
of the signature policy; and
- be a registered type, in which case, the commitment type has
precise semantics defined by registration, under the rules of
the registration authority. Such a registration authority may
be a trading association or a legislative authority.
The signature policy specifies a set of attributes that it
"recognizes". This "recognized" set includes all those commitment
types defined as part of the signature policy, as well as any
externally defined commitment types that the policy may choose to
recognize. Only recognized commitment types are allowed in this
field.
The following object identifier identifies the
commitment-type-indication attribute:
id-aa-ets-commitmentType OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 16}
commitment-type-indication attribute values have ASN.1 type
CommitmentTypeIndication.
CommitmentTypeIndication ::= SEQUENCE {
commitmentTypeId CommitmentTypeIdentifier,
commitmentTypeQualifier SEQUENCE SIZE (1..MAX) OF
CommitmentTypeQualifier OPTIONAL}
CommitmentTypeIdentifier ::= OBJECT IDENTIFIER
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CommitmentTypeQualifier ::= SEQUENCE {
commitmentTypeIdentifier CommitmentTypeIdentifier,
qualifier ANY DEFINED BY commitmentTypeIdentifier }
The use of any qualifiers to the commitment type is outside the scope
of the present document.
The following generic commitment types are defined in the present
document:
id-cti-ets-proofOfOrigin OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 1}
id-cti-ets-proofOfReceipt OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 2}
id-cti-ets-proofOfDelivery OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
cti(6) 3}
id-cti-ets-proofOfSender OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 4}
id-cti-ets-proofOfApproval OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
cti(6) 5}
id-cti-ets-proofOfCreation OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
cti(6) 6}
These generic commitment types have the following meanings:
Proof of origin indicates that the signer recognizes to have created,
approved, and sent the message.
Proof of receipt indicates that signer recognizes to have received
the content of the message.
Proof of delivery indicates that the TSP providing that indication
has delivered a message in a local store accessible to the recipient
of the message.
Proof of sender indicates that the entity providing that indication
has sent the message (but not necessarily created it).
Proof of approval indicates that the signer has approved the content
of the message.
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Proof of creation indicates that the signer has created the message
(but not necessarily approved, nor sent it).
5.11.2. signer-location Attribute
The signer-location attribute specifies a mnemonic for an address
associated with the signer at a particular geographical (e.g., city)
location. The mnemonic is registered in the country in which the
signer is located and is used in the provision of the Public Telegram
Service (according to ITU-T Recommendation F.1 [11]).
The signer-location attribute shall be a signed attribute. The
following object identifier identifies the signer-location attribute:
id-aa-ets-signerLocation OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 17}
Signer-location attribute values have ASN.1 type SignerLocation:
SignerLocation ::= SEQUENCE {
-- at least one of the following shall be present:
countryName [0] DirectoryString OPTIONAL,
-- As used to name a Country in X.500
localityName [1] DirectoryString OPTIONAL,
-- As used to name a locality in X.500
postalAdddress [2] PostalAddress OPTIONAL }
PostalAddress ::= SEQUENCE SIZE(1..6) OF DirectoryString
5.11.3. signer-attributes Attribute
The signer-attributes attribute specifies additional attributes of
the signer (e.g., role). It may be either:
- claimed attributes of the signer; or
- certified attributes of the signer.
The signer-attributes attribute shall be a signed attribute. The
following object identifier identifies the signer-attribute
attribute:
id-aa-ets-signerAttr OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 18}
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signer-attributes values have ASN.1 type SignerAttribute:
SignerAttribute ::= SEQUENCE OF CHOICE {
claimedAttributes [0] ClaimedAttributes,
certifiedAttributes [1] CertifiedAttributes }
ClaimedAttributes ::= SEQUENCE OF Attribute
CertifiedAttributes ::= AttributeCertificate
-- as defined in RFC 3281: see Section 4.1.
NOTE 1: Only a single signer-attributes can be used.
NOTE 2: Attribute and AttributeCertificate are as defined
respectively in ITU-T Recommendations X.501 [9] and X.509 [1].
5.11.4. content-time-stamp Attribute
The content-time-stamp attribute is an attribute that is the
time-stamp token of the signed data content before it is signed. The
content-time-stamp attribute shall be a signed attribute.
The following object identifier identifies the content-time-stamp
attribute:
id-aa-ets-contentTimestamp OBJECT IDENTIFIER ::=
{ iso(1) member- body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 20}
content-time-stamp attribute values have ASN.1 type ContentTimestamp:
ContentTimestamp ::= TimeStampToken
The value of messageImprint of TimeStampToken (as described in RFC
3161 [7]) shall be a hash of the value of the eContent field within
encapContentInfo in the signedData.
For further information and definition of TimeStampToken, see Section
7.4.
NOTE: content-time-stamp indicates that the signed information was
formed before the date included in the content-time-stamp.
5.12. Support for Multiple Signatures
5.12.1. Independent Signatures
Multiple independent signatures (see Annex B.5) are supported by
independent SignerInfo from each signer.
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Each SignerInfo shall include all the attributes required under the
present document and shall be processed independently by the
verifier.
NOTE: Independent signatures may be used to provide independent
signatures from different parties with different signed
attributes, or to provide multiple signatures from the same party
using alternative signature algorithms, in which case the other
attributes, excluding time values and signature policy
information, will generally be the same.
5.12.2. Embedded Signatures
Multiple embedded signatures (see Annex C.5) are supported using the
countersignature unsigned attribute (see Section 5.9.2). Each
counter signature is carried in countersignature held as an unsigned
attribute to the SignerInfo to which the counter-signature is
applied.
NOTE: Counter signatures may be used to provide signatures from
different parties with different signed attributes, or to provide
multiple signatures from the same party using alternative
signature algorithms, in which case the other attributes,
excluding time values and signature policy information, will
generally be the same.
6. Additional Electronic Signature Validation Attributes
This section specifies attributes that contain different types of
validation data. These attributes build on the electronic signature
specified in Section 5. This includes:
- Signature-time-stamp applied to the electronic signature value
or a Time-Mark in an audit trail. This is defined as the
Electronic Signature with Time (CAdES-T); and
- Complete validation data references that comprise the time-stamp
of the signature value, plus references to all the certificates
(complete-certificate-references) and revocation (complete-
revocation-references) information used for full validation of
the electronic signature. This is defined as the Electronic
Signature with Complete data references (CAdES-C).
NOTE 1: Formats for CAdES-T are illustrated in Section 4.4, and
the attributes are defined in Section 6.1.1.
Pinkas, et al. Informational [Page 45]RFC 5126 CMS Advanced Electronic Signatures February 2008
NOTE 2: Formats for CAdES-C are illustrated in Section 4.4. The
required attributes for the CAdES-C signature format are defined
in Sections 6.2.1 to 6.2.2; optional attributes are defined in
Sections 6.2.3 and 6.2.4.
In addition, the following optional extended forms of validation data
are also defined; see Annex B for an overview of the extended forms
of validation data:
- CAdES-X with time-stamp: there are two types of time-stamps used
in extended validation data defined by the present document;
- Type 1(CAdES-X Type 1): comprises a time-stamp over the ES
with Complete validation data (CAdES-C); and
- Type 2 (CAdES-X Type2): comprises a time-stamp over the
certification path references and the revocation information
references used to support the CAdES-C.
NOTE 3: Formats for CAdES-X Type 1 and CAdES-X Type 2 are
illustrated in Sections B.1.2 and B.1.3, respectively.
- CAdES-X Long: comprises the Complete validation data
references (CAdES-C), plus the actual values of all the
certificates and revocation information used in the CAdES-C.
NOTE 4: Formats for CAdES-X Long are illustrated in Annex B.1.1.
- CAdES-X Long Type 1 or CAdES-X Long Type 2: comprises an
X-Time-Stamp (Type 1 or Type 2), plus the actual values of
all the certificates and revocation information used in the
CAdES-C as per CAdES-X Long.
This section also specifies the data structures used in Archive
validation data format (CAdES-A)of extended forms:
- Archive form of electronic signature (CAdES-A) comprises:
- the Complete validation data references (CAdES-C),
- the certificate and revocation values (as in a CAdES-X Long ),
- any existing extended electronic signature time-stamps
(CAdES-X Type 1 or CAdES-X Type 2), if present, and
- the signed user data and an additional archive time-stamp
applied over all that data.
Pinkas, et al. Informational [Page 46]RFC 5126 CMS Advanced Electronic Signatures February 2008
An archive time-stamp may be repeatedly applied after long
periods to maintain validity when electronic signature and
time-stamping algorithms weaken.
The additional data required to create the forms of electronic
signature identified above is carried as unsigned attributes
associated with an individual signature by being placed in the
unsignedAttrs field of SignerInfo. Thus, all the attributes defined
in Section 6 are unsigned attributes.
NOTE 5: Where multiple signatures are to be supported, as
described in Section 5.12, each signature has a separate
SignerInfo. Thus, each signature requires its own unsigned
attribute values to create CAdES-T, CAdES-C, etc.
NOTE 6: The optional attributes of the extended validation data
are defined in Sections 6.3 and 6.4.
6.1. signature time-stamp Attribute (CAdES-T)
An electronic signature with time-stamp is an electronic signature
for which part, but not all, of the additional data required for
validation is available (i.e., some certificates and revocation
information are available, but not all).
The minimum structure time-stamp validation data is:
- the signature time-stamp attribute, as defined in Section 6.1.1,
over the ES signature value.
6.1.1. signature-time-stamp Attribute Definition
The signature-time-stamp attribute is a TimeStampToken computed on
the signature value for a specific signer; it is an unsigned
attribute. Several instances of this attribute may occur with an
electronic signature, from different TSAs.
The following object identifier identifies the signature-time-stamp
attribute:
id-aa-signatureTimeStampToken OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 14}
The signature-time-stamp attribute value has ASN.1 type
SignatureTimeStampToken:
SignatureTimeStampToken ::= TimeStampToken
Pinkas, et al. Informational [Page 47]RFC 5126 CMS Advanced Electronic Signatures February 2008
The value of the messageImprint field within TimeStampToken shall be
a hash of the value of the signature field within SignerInfo for the
signedData being time-stamped.
For further information and definition of TimeStampToken, see Section
7.4.
NOTE 1: In the case of multiple signatures, it is possible to have
a:
- TimeStampToken computed for each and all signers; or
- TimeStampToken computed on one signer's signature; and no
- TimeStampToken on another signer's signature.
NOTE 2: In the case of multiple signatures, several TSTs, issued
by different TSAs, may be present within the same signerInfo (see
RFC 3852 [4]).
6.2. Complete Validation Data References (CAdES-C)
An electronic signature with Complete validation data references
(CAdES-C) is an electronic signature for which all the additional
data required for validation (i.e., all certificates and revocation
information) is available. This form is built on the CAdES-T form
defined above.
As a minimum, the Complete validation data shall include the
following:
- a time, which shall either be a signature-timestamp attribute,
as defined in Section 6.1.1, or a time-mark operated by a
Time-Marking Authority;
- complete-certificate-references, as defined in Section 6.2.1;
- complete-revocation-references, as defined in Section 6.2.2.
6.2.1. complete-certificate-references Attribute Definition
The complete-certificate-references attribute is an unsigned
attribute. It references the full set of CA certificates that have
been used to validate an ES with Complete validation data up to (but
not including) the signer's certificate. Only a single instance of
this attribute shall occur with an electronic signature.
Pinkas, et al. Informational [Page 48]RFC 5126 CMS Advanced Electronic Signatures February 2008
NOTE 1: The signer's certificate is referenced in the signing
certificate attribute (see Section 5.7.3).
id-aa-ets-certificateRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 21}
The complete-certificate-references attribute value has the ASN.1
syntax CompleteCertificateRefs.
CompleteCertificateRefs ::= SEQUENCE OF OtherCertID
OtherCertID is defined in Section 5.7.3.3.
The IssuerSerial that shall be present in OtherCertID. The certHash
shall match the hash of the certificate referenced.
NOTE 2: Copies of the certificate values may be held using the
certificate-values attribute, defined in Section 6.3.3.
This attribute may include references to the certification chain
for any TSUs that provides time-stamp tokens. In this case, the
unsigned attribute shall be added to the signedData of the
relevant time-stamp token as an unsignedAttrs in the signerInfos
field.
6.2.2. complete-revocation-references Attribute Definition
The complete-revocation-references attribute is an unsigned
attribute. Only a single instance of this attribute shall occur with
an electronic signature. It references the full set of the CRL,
ACRL, or OCSP responses that have been used in the validation of the
signer, and CA certificates used in ES with Complete validation data.
This attribute indicates that the verifier has taken due diligence to
gather the available revocation information. The references stored
in this attribute can be used to retrieve the referenced information,
if not stored in the CMS structure, but somewhere else.
The following object identifier identifies the
complete-revocation-references attribute:
id-aa-ets-revocationRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 22}
Pinkas, et al. Informational [Page 49]RFC 5126 CMS Advanced Electronic Signatures February 2008
The complete-revocation-references attribute value has the ASN.1
syntax CompleteRevocationRefs:
CompleteRevocationRefs ::= SEQUENCE OF CrlOcspRef
CrlOcspRef ::= SEQUENCE {
crlids [0] CRLListID OPTIONAL,
ocspids [1] OcspListID OPTIONAL,
otherRev [2] OtherRevRefs OPTIONAL
}
CompleteRevocationRefs shall contain one CrlOcspRef for the
signing-certificate, followed by one for each OtherCertID in the
CompleteCertificateRefs attribute. The second and subsequent
CrlOcspRef fields shall be in the same order as the OtherCertID to
which they relate. At least one of CRLListID or OcspListID or
OtherRevRefs should be present for all but the "trusted" CA of the
certificate path.
CRLListID ::= SEQUENCE {
crls SEQUENCE OF CrlValidatedID }
CrlValidatedID ::= SEQUENCE {
crlHash OtherHash,
crlIdentifier CrlIdentifier OPTIONAL }
CrlIdentifier ::= SEQUENCE {
crlissuer Name,
crlIssuedTime UTCTime,
crlNumber INTEGER OPTIONAL }
OcspListID ::= SEQUENCE {
ocspResponses SEQUENCE OF OcspResponsesID }
OcspResponsesID ::= SEQUENCE {
ocspIdentifier OcspIdentifier,
ocspRepHash OtherHash OPTIONAL
}
OcspIdentifier ::= SEQUENCE {
ocspResponderID ResponderID,
-- As in OCSP response data
producedAt GeneralizedTime
-- As in OCSP response data
}
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When creating a crlValidatedID, the crlHash is computed over the
entire DER encoded CRL including the signature. The crlIdentifier
would normally be present unless the CRL can be inferred from other
information.
The crlIdentifier is to identify the CRL using the issuer name and
the CRL issued time, which shall correspond to the time thisUpdate
contained in the issued CRL, and if present, the crlNumber. The
crlListID attribute is an unsigned attribute. In the case that the
identified CRL is a Delta CRL, then references to the set of CRLs to
provide a complete revocation list shall be included.
The OcspIdentifier is to identify the OCSP response using the issuer
name and the time of issue of the OCSP response, which shall
correspond to the time produced as contained in the issued OCSP
response. Since it may be needed to make the difference between two
OCSP responses received within the same second, the hash of the
response contained in the OcspResponsesID may be needed to solve the
ambiguity.
NOTE 1: Copies of the CRL and OCSP responses values may be held
using the revocation-values attribute defined in Section 6.3.4.
NOTE 2: It is recommended that this attribute be used in
preference to the OtherRevocationInfoFormat specified in RFC 3852
to maintain backwards compatibility with the earlier version of
this specification.
The syntax and semantics of other revocation references are outside
the scope of the present document. The definition of the syntax of
the other form of revocation information is as identified by
OtherRevRefType.
This attribute may include the references to the full set of the CRL,
ACRL, or OCSP responses that have been used to verify the
certification chain for any TSUs that provide time-stamp tokens. In
this case, the unsigned attribute shall be added to the signedData of
the relevant time-stamp token as an unsignedAttrs in the signerInfos
field.
6.2.3. attribute-certificate-references Attribute Definition
This attribute is only used when a user attribute certificate is
present in the electronic signature.
The attribute-certificate-references attribute is an unsigned
attribute. It references the full set of AA certificates that have
Pinkas, et al. Informational [Page 51]RFC 5126 CMS Advanced Electronic Signatures February 2008
been used to validate the attribute certificate. Only a single
instance of this attribute shall occur with an electronic signature.
id-aa-ets-attrCertificateRefs OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 44}
The attribute-certificate-references attribute value has the ASN.1
syntax AttributeCertificateRefs:
AttributeCertificateRefs ::= SEQUENCE OF OtherCertID
OtherCertID is defined in Section 5.7.3.3.
NOTE: Copies of the certificate values may be held using the
certificate-values attribute defined in Section 6.3.3.
6.2.4. attribute-revocation-references Attribute Definition
This attribute is only used when a user attribute certificate is
present in the electronic signature and when that attribute
certificate can be revoked.
The attribute-revocation-references attribute is an unsigned
attribute. Only a single instance of this attribute shall occur with
an electronic signature. It references the full set of the ACRL or
OCSP responses that have been used in the validation of the attribute
certificate. This attribute can be used to illustrate that the
verifier has taken due diligence of the available revocation
information.
The following object identifier identifies the
attribute-revocation-references attribute:
id-aa-ets-attrRevocationRefs OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
id-aa(2) 45}
The attribute-revocation-references attribute value has the ASN.1
syntax AttributeRevocationRefs:
AttributeRevocationRefs ::= SEQUENCE OF CrlOcspRef
6.3. Extended Validation Data (CAdES-X)
This section specifies a number of optional attributes that are used
by extended forms of electronic signatures (see Annex B for an
overview of these forms of validation data).
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6.3.1. Time-Stamped Validation Data (CAdES-X Type 1 or Type 2)
The extended validation data may include one of the following
additional attributes, forming a CAdES-X Time-Stamp validation data
(CAdES-X Type 1 or CAdES-X Type 2), to provide additional protection
against later CA compromise and provide integrity of the validation
data used:
- CAdES-C Time-stamp, as defined in Section 6.3.5 (CAdES-X Type
1); or
- Time-Stamped Certificates and CRLs references, as defined in
Section 6.3.6 (CAdES-X Type 2).
6.3.2. Long Validation Data (CAdES-X Long, CAdES-X Long Type 1 or 2)
The extended validation data may also include the following
additional information, forming a CAdES-X Long, for use if later
validation processes may not have access to this information:
- certificate-values, as defined in Section 6.3.3; and
- revocation-values, as defined in Section 6.3.4.
The extended validation data may, in addition to certificate-values
and revocation-values as defined in Sections 6.3.3 and 6.3.4, include
one of the following additional attributes, forming a CAdES-X Long
Type 1 or CAdES-X Long Type 2.
- CAdES-C Time-stamp, as defined in Section 6.3.3 (CAdES-X long
Type 1); or
- Time-Stamped Certificates and CRLs references, as defined in
Section 6.3.4 (CAdES-X Long Type 2).
The CAdES-X Long Type 1 or CAdES-X Long Type 2 provides additional
protection against later CA compromise and provides integrity of the
validation data used.
NOTE 1: The CAdES-X-Long signature provides long-term proof of the
validity of the signature for as long as the CA keys, CRL Issuers
keys, and OCSP responder keys are not compromised and are
resistant to cryptographic attacks.
NOTE 2: As long as the time-stamp data remains valid, the CAdES-X
Long Type 1 and the CAdES-X Long Type 2 provide the following
important property for long-standing signatures; that having been
found once to be valid, it shall continue to be so months or years
Pinkas, et al. Informational [Page 53]RFC 5126 CMS Advanced Electronic Signatures February 2008
later, long after the validity period of the certificates has
expired, or after the user key has been compromised.
6.3.3. certificate-values Attribute Definition
This attribute may be used to contain the certificate information
required for the following forms of extended electronic signature:
CAdES-X Long, ES X-Long Type 1, and CAdES-X Long Type 2; see Annex
B.1.1 for an illustration of this form of electronic signature.
The certificate-values attribute is an unsigned attribute. Only a
single instance of this attribute shall occur with an electronic
signature. It holds the values of certificates referenced in the
complete-certificate-references attribute.
NOTE: If an attribute certificate is used, it is not provided in
this structure but shall be provided by the signer as a
signer-attributes attribute (see Section 5.11.3).
The following object identifier identifies the certificate-values
attribute:
id-aa-ets-certValues OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 23}
The certificate-values attribute value has the ASN.1 syntax
CertificateValues.
CertificateValues ::= SEQUENCE OF Certificate
Certificate is defined in Section 7.1. (which is as defined in ITU-T
Recommendation X.509 [1]).
This attribute may include the certification information for any TSUs
that have provided the time-stamp tokens, if these certificates are
not already included in the TSTs as part of the TSUs signatures. In
this case, the unsigned attribute shall be added to the signedData of
the relevant time-stamp token.
6.3.4. revocation-values Attribute Definition
This attribute is used to contain the revocation information required
for the following forms of extended electronic signature: CAdES-X
Long, ES X-Long Type 1, and CAdES-X Long Type 2; see Annex B.1.1 for
an illustration of this form of electronic signature.
The revocation-values attribute is an unsigned attribute. Only a
single instance of this attribute shall occur with an electronic
Pinkas, et al. Informational [Page 54]RFC 5126 CMS Advanced Electronic Signatures February 2008
signature. It holds the values of CRLs and OCSP referenced in the
complete-revocation-references attribute.
NOTE: It is recommended that this attribute be used in preference
to the OtherRevocationInfoFormat specified in RFC 3852 to maintain
backwards compatibility with the earlier version of this
specification.
The following object identifier identifies the revocation-values
attribute:
id-aa-ets-revocationValues OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 24}
The revocation-values attribute value has the ASN.1 syntax
RevocationValues
RevocationValues ::= SEQUENCE {
crlVals [0] SEQUENCE OF CertificateList OPTIONAL,
ocspVals [1] SEQUENCE OF BasicOCSPResponse OPTIONAL,
otherRevVals [2] OtherRevVals OPTIONAL }
OtherRevVals ::= SEQUENCE {
OtherRevValType OtherRevValType,
OtherRevVals ANY DEFINED BY OtherRevValType }
OtherRevValType ::= OBJECT IDENTIFIER
The syntax and semantics of the other revocation values
(OtherRevVals) are outside the scope of the present document.
The definition of the syntax of the other form of revocation
information is as identified by OtherRevRefType.
CertificateList is defined in Section 7.2. (which is as defined in
ITU-T Recommendation X.509 [1]).
BasicOCSPResponse is defined in Section 7.3. (which is as defined in
RFC 2560 [3]).
This attribute may include the values of revocation data including
CRLs and OCSPs for any TSUs that have provided the time-stamp tokens,
if these certificates are not already included in the TSTs as part of
the TSUs signatures. In this case, the unsigned attribute shall be
added to the signedData of the relevant time-stamp token.
Pinkas, et al. Informational [Page 55]RFC 5126 CMS Advanced Electronic Signatures February 2008
6.3.5. CAdES-C-time-stamp Attribute Definition
This attribute is used to protect against CA key compromise.
This attribute is used for the time-stamping of the complete
electronic signature (CAdES-C). It is used in the following forms of
extended electronic signature; CAdES-X Type 1 and CAdES-X Long Type
1; see Annex B.1.2 for an illustration of this form of electronic
signature.
The CAdES-C-time-stamp attribute is an unsigned attribute. It is a
time-stamp token of the hash of the electronic signature and the
complete validation data (CAdES-C). It is a special-purpose
TimeStampToken Attribute that time-stamps the CAdES-C. Several
instances of this attribute may occur with an electronic signature
from different TSAs.
NOTE 1: It is recommended that the attributes being time-stamped
be encoded in DER. If DER is not employed, then the binary
encoding of the ASN.1 structures being time-stamped should be
preserved to ensure that the recalculation of the data hash is
consistent.
NOTE 2: Each attribute is included in the hash with the attrType
and attrValues (including type and length) but without the type
and length of the outer SEQUENCE.
The following object identifier identifies the CAdES-C-Timestamp
attribute:
id-aa-ets-escTimeStamp OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 25}
The CAdES-C-timestamp attribute value has the ASN.1 syntax
ESCTimeStampToken :
ESCTimeStampToken ::= TimeStampToken
The value of the messageImprint field within TimeStampToken shall be
a hash of the concatenated values (without the type or length
encoding for that value) of the following data objects:
- OCTETSTRING of the SignatureValue field within SignerInfo;
- signature-time-stamp, or a time-mark operated by a Time-Marking
Authority;
- complete-certificate-references attribute; and
Pinkas, et al. Informational [Page 56]RFC 5126 CMS Advanced Electronic Signatures February 2008
- complete-revocation-references attribute.
For further information and definition of the TimeStampToken, see
Section 7.4.
6.3.6. time-stamped-certs-crls-references Attribute Definition
This attribute is used to protect against CA key compromise. This
attribute is used for the time-stamping certificate and revocation
references. It is used in the following forms of extended electronic
signature: CAdES-X Type 2 and CAdES-X Long Type 2; see Annex B.1.3
for an illustration of this form of electronic signature.
A time-stamped-certs-crls-references attribute is an unsigned
attribute. It is a time-stamp token issued for a list of referenced
certificates and OCSP responses and/or CRLs to protect against
certain CA compromises. Its syntax is as follows:
NOTE 1: It is recommended that the attributes being time-stamped
be encoded in DER. If DER is not employed, then the binary
encoding of the ASN.1 structures being time-stamped should be
preserved to ensure that the recalculation of the data hash is
consistent.
NOTE 2: Each attribute is included in the hash with the attrType
and attrValues (including type and length) but without the type
and length of the outer SEQUENCE.
The following object identifier identifies the
time-stamped-certs-crls-references attribute:
id-aa-ets-certCRLTimestamp OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 26}
The attribute value has the ASN.1 syntax TimestampedCertsCRLs:
TimestampedCertsCRLs ::= TimeStampToken
The value of the messageImprint field within the TimeStampToken shall
be a hash of the concatenated values (without the type or length
encoding for that value) of the following data objects, as present in
the ES with Complete validation data (CAdES-C):
- complete-certificate-references attribute; and
- complete-revocation-references attribute.
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6.4. Archive Validation Data
Where an electronic signature is required to last for a very long
time, and the time-stamp token on an electronic signature is in
danger of being invalidated due to algorithm weakness or limits in
the validity period of the TSA certificate, it may be required to
time-stamp the electronic signature several times. When this is
required, an archive time-stamp attribute may be required for the
archive form of the electronic signature (CAdES-A). This archive
time-stamp attribute may be repeatedly applied over a period of time.
6.4.1. archive-time-stamp Attribute Definition
The archive-time-stamp attribute is a time-stamp token of many of the
elements of the signedData in the electronic signature. If the
certificate-values and revocation-values attributes are not present
in the CAdES-BES or CAdES-EPES, then they shall be added to the
electronic signature prior to computing the archive time-stamp token.
The archive-time-stamp attribute is an unsigned attribute. Several
instances of this attribute may occur with an electronic signature
both over time and from different TSUs.
The following object identifier identifies the nested
archive-time-stamp attribute:
id-aa-ets-archiveTimestampV2 OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 48}
Archive-time-stamp attribute values have the ASN.1 syntax
ArchiveTimeStampToken
ArchiveTimeStampToken ::= TimeStampToken
The value of the messageImprint field within TimeStampToken shall be
a hash of the concatenation of:
- the encapContentInfo element of the SignedData sequence;
- any external content being protected by the signature, if the
eContent element of the encapContentInfo is omitted;
- the Certificates and crls elements of the SignedData sequence,
when present, and;
- all data elements in the SignerInfo sequence including all
signed and unsigned attributes.
Pinkas, et al. Informational [Page 58]RFC 5126 CMS Advanced Electronic Signatures February 2008
NOTE 1: An alternative archiveTimestamp attribute, identified by
an object identifier { iso(1) member-body(2) us(840)
rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 27, is defined
in prior versions of TS 101 733 [TS101733] and in RFC 3126.
The archiveTimestamp attribute, defined in versions of TS 101 733
prior to 1.5.1 and in RFC 3126, is not compatible with the
attribute defined in the current document. The archiveTimestamp
attribute, defined in versions 1.5.1 to 1.6.3 of TS 101 733, is
compatible with the current document if the content is internal to
encapContentInfo. Unless the version of TS 101 733 employed by
the signing party is known by all recipients, use of the
archiveTimestamp attribute defined in prior versions of TS 101 733
is deprecated.
NOTE 2: Counter signatures held as countersignature attributes do
not require independent archive time-stamps, as they are protected
by the archive time-stamp against the containing SignedData
structure.
NOTE 3: Unless DER is used throughout, it is recommended that the
binary encoding of the ASN.1 structures being time-stamped be
preserved when being archived to ensure that the recalculation of
the data hash is consistent.
NOTE 4: The hash is calculated over the concatenated data elements
as received/stored, including the Type and Length encoding.
NOTE 5: Whilst it is recommended that unsigned attributes be DER
encoded, it cannot generally be so guaranteed except by prior
arrangement. For further information and definition of
TimeStampToken, see Section 7.4. The timestamp should be created
using stronger algorithms (or longer key lengths) than in the
original electronic signatures and weak algorithm (key length)
timestamps.
NOTE 6: This form of ES also provides protection against a TSP key
compromise.
The ArchiveTimeStamp will be added as an unsigned attribute in the
SignerInfo sequence. For the validation of one ArchiveTimeStamp, the
data elements of the SignerInfo must be concatenated, excluding all
later ArchivTimeStampToken attributes.
Certificates and revocation information required to validate the
ArchiveTimeStamp shall be provided by one of the following methods:
Pinkas, et al. Informational [Page 59]RFC 5126 CMS Advanced Electronic Signatures February 2008
- The TSU provides the information in the SignedData of the
timestamp token;
- Adding the complete-certificate-references attribute and the
complete-revocation-references attribute of the TSP as an
unsigned attribute within TimeStampToken, when the required
information is stored elsewhere; or
- Adding the certificate-values attribute and the
revocation-values attribute of the TSP as an unsigned attribute
within TimeStampToken, when the required information is stored
elsewhere.
7. Other Standard Data Structures
7.1. Public Key Certificate Format
The X.509 v3 certificate basis syntax is defined in ITU-T
Recommendation X.509 [1]. A profile of the X.509 v3 certificate is
defined in RFC 3280 [2].
7.2. Certificate Revocation List Format
The X.509 v2 CRL syntax is defined in ITU-T Recommendation X.509 [1].
A profile of the X.509 v2 CRL is defined in RFC 3280 [2].
7.3. OCSP Response Format
The format of an OCSP token is defined in RFC 2560 [3].
7.4. Time-Stamp Token Format
The format of a TimeStampToken type is defined in RFC 3161 [7] and
profiled in ETSI TS 101 861 [TS101861].
7.5. Name and Attribute Formats
The syntax of the naming and other attributes is defined in ITU-T
Recommendation X.509 [1].
NOTE: The name used by the signer, held as the subject in the
signer's certificate, is allocated and verified on registration
with the Certification Authority, either directly or indirectly
through a Registration Authority, before being issued with a
Certificate.
Pinkas, et al. Informational [Page 60]RFC 5126 CMS Advanced Electronic Signatures February 2008
The present document places no restrictions on the form of the name.
The subject's name may be a distinguished name, as defined in ITU-T
Recommendation X.500 [12], held in the subject field of the
certificate, or any other name form held in the subjectAltName
certificate extension field, as defined in ITU-T Recommendation X.509
[1]. In the case that the subject has no distinguished name, the
subject name can be an empty sequence and the subjectAltName
extension shall be critical.
All Certification Authorities, Attribute Authorities, and
Time-Stamping Authorities shall use distinguished names in the
subject field of their certificate.
The distinguished name shall include identifiers for the organization
providing the service and the legal jurisdiction (e.g., country)
under which it operates.
Where a signer signs as an individual, but wishes to also identify
him/herself as acting on behalf of an organization, it may be
necessary to provide two independent forms of identification. The
first identity, which is directly associated with the signing key,
identifies him/her as an individual. The second, which is managed
independently, identifies that person acting as part of the
organization, possibly with a given role. In this case, one of the
two identities is carried in the subject/subjectAltName field of the
signer's certificate as described above.
The present document does not specify the format of the signer's
attribute that may be included in public key certificates.
NOTE: The signer's attribute may be supported by using a claimed
role in the CMS signed attributes field or by placing an attribute
certificate containing a certified role in the CMS signed
attributes field; see Section 7.6.
7.6. AttributeCertificate
The syntax of the AttributeCertificate type is defined in RFC 3281
[13].
8. Conformance Requirements
For implementations supporting signature generation, the present
document defines conformance requirements for the generation of two
forms of basic electronic signature, one of the two forms must be
implemented.
Pinkas, et al. Informational [Page 61]RFC 5126 CMS Advanced Electronic Signatures February 2008
For implementations supporting signature verification, the present
document defines conformance requirements for the verification of two
forms of basic electronic signature, one of the two forms must be
implemented.
The present document only defines conformance requirements up to an
ES with Complete validation data (CAdES-C). This means that none of
the extended and archive forms of the electronic signature (CAdES-X,
CAdES-A) need to be implemented to get conformance to the present
document.
On verification the inclusion of optional signed and unsigned
attributes must be supported only to the extent that the signature is
verifiable. The semantics of optional attributes may be unsupported,
unless specified otherwise by a signature policy.
8.1. CAdES-Basic Electronic Signature (CAdES-BES)
A system supporting CAdES-BES signers, according to the present
document, shall, at a minimum, support generation of an electronic
signature consisting of the following components:
- The general CMS syntax and content type, as defined in RFC 3852
[4] (see Sections 5.1 and 5.2);
- CMS SignedData, as defined in RFC 3852 [4], with the version set
to 3 and at least one SignerInfo present (see Sections 5.3 to
5.6);
- The following CMS attributes, as defined in RFC 3852 [4]:
- content-type; this shall always be present (see Section
5.7.1); and
- message-digest; this shall always be present (see Section
5.7.2).
- One of the following attributes, as defined in the present
document:
- signing-certificate: as defined in Section 5.7.3.1; or
- signing-certificate v2 : as defined in Section 5.7.3.2.
NOTE: RFC 3126 was using the other signing-certificate attribute
(see Section 5.7.3.3). Its use is now deprecated, since the
structure of the signing-certificate v2 attribute is simpler than
the other signing-certificate attribute.
Pinkas, et al. Informational [Page 62]RFC 5126 CMS Advanced Electronic Signatures February 2008
8.2. CAdES-Explicit Policy-based Electronic Signature
A system supporting Policy-based signers, according to the present
document, shall, at a minimum, support the generation of an
electronic signature consisting of the previous components defined
for the basic signer, plus:
- The following attributes, as defined in Section 5.9:
- signature-policy-identifier; this shall always be present
(see Section 5.8.1).
8.3. Verification Using Time-Stamping
A system supporting verifiers, according to the present document,
with time-stamping facilities shall, at a minimum, support:
- verification of the mandated components of an electronic
signature, as defined in Section 8.1;
- signature-time-stamp attribute, as defined in Section 6.1.1;
- complete-certificate-references attribute, as defined in Section
6.2.1;
- complete-revocation-references attribute, as defined in Section
6.2.2;
- Public Key Certificates, as defined in ITU-T Recommendation
X.509 [1] (see Section 8.1); and
- either of:
- Certificate Revocation Lists, as defined in ITU-T
Recommendation X.509 [1] (see Section 8.2); or
- Online Certificate Status Protocol, as defined in RFC 2560
[3] (see Section 8.3).
8.4. Verification Using Secure Records
A system supporting verifiers, according to the present document,
shall, at a minimum, support:
- verification of the mandated components of an electronic
signature, as defined in Section 8.1;
Pinkas, et al. Informational [Page 63]RFC 5126 CMS Advanced Electronic Signatures February 2008
- complete-certificate-references attribute, as defined in Section
6.2.1;
- complete-revocation-references attribute, as defined in Section
6.2.2;
- a record of the electronic signature and the time when the
signature was first validated, using the referenced certificates
and revocation information, must be maintained, such that
records cannot be undetectably modified;
- Public Key Certificates, as defined in ITU-T Recommendation
X.509 [1] (see Section 8.1); and
- either of:
- Certificate Revocation Lists, as defined in ITU-T
Recommendation X.509 [1] (see Section 8.2); or
- online Certificate Status Protocol, as defined in RFC 2560
[3] (see Section 8.3).
9. References
9.1. Normative References
[1] ITU-T Recommendation X.509 (2000)/ISO/IEC 9594-8 (2001):
"Information technology - Open Systems Interconnection - The
Directory: Public key and Attribute Certificate framework".
[2] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet X.509
Public Key Infrastructure Certificate and Certificate
Revocation List (CRL) Profile", RFC 3280, April 2002.
[3] Myers, M., Ankney, R., Malpani, A., Galperin, S., and C.
Adams, "X.509 Internet Public Key Infrastructure Online
Certificate Status Protocol - OCSP", RFC 2560, June 1999.
[4] Housley, R., "Cryptographic Message Syntax (CMS)", RFC 3852,
July 2004.
[5] Hoffman, P., Ed., "Enhanced Security Services for S/MIME", RFC
2634, June 1999.
[6] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
Pinkas, et al. Informational [Page 64]RFC 5126 CMS Advanced Electronic Signatures February 2008
[7] Adams, C., Cain, P., Pinkas, D., and R. Zuccherato, "Internet
X.509 Public Key Infrastructure Time-Stamp Protocol (TSP)",
RFC 3161, August 2001.
[8] ITU-T Recommendation X.680 (1997): "Information technology -
Abstract Syntax Notation One (ASN.1): Specification of basic
notation".
[9] ITU-T Recommendation X.501 (2000)/ISO/IEC 9594-1 (2001):
"Information technology - Open Systems Interconnection -
Directory models".
[10] Housley, R., "Cryptographic Message Syntax (CMS) Algorithms",
RFC 3370, August 2002.
[11] ITU-T Recommendation F.1: "Operational provisions for the
international public telegram service".
[12] ITU-T Recommendation X.500: "Information technology - Open
Systems Interconnection - The Directory: Overview of concepts,
models and services".
[13] Farrell, S. and R. Housley, "An Internet Attribute Certificate
Profile for Authorization", RFC 3281, April 2002.
[14] ITU-T Recommendation X.208 (1988): "Specification of Abstract
Syntax Notation One (ASN.1)".
[15] Schaad, J., "Enhanced Security Services (ESS) Update: Adding
CertID Algorithm Agility", RFC 5035, August 2007.
[16] ITU-T Recommendation X.690 (2002): "Information technology
ASN.1 encoding rules: Specification of Basic Encoding Rules
(BER), Canonical Encoding Rules (CER) and Distinguished
Encoding Rules (DER)".
9.2. Informative References
[EUDirective] Directive 1999/93/EC of the European Parliament and of
the Council of 13 December 1999 on a community
framework for Electronic Signatures.
[TS101733] ETSI Standard TS 101 733 V.1.7.3 (2005-06) Electronic
Signature Formats.
[TS101861] ETSI TS 101 861: "Time stamping profile".
Pinkas, et al. Informational [Page 65]RFC 5126 CMS Advanced Electronic Signatures February 2008
[TS101903] ETSI TS 101 903: "XML Advanced Electronic Signatures
(XAdES)".
[TR102038] ETSI TR 102 038: "Electronic Signatures and
Infrastructures (ESI); XML format for signature
policies".
[TR102272] ETSI TR 102 272 V1.1.1 (2003-12). "Electronic
Signatures and Infrastructures (ESI); ASN.1 format for
signature policies".
[RFC2479] Adams, C., "Independent Data Unit Protection Generic
Security Service Application Program Interface (IDUP-
GSS-API)", RFC 2479, December 1998.
[RFC2743] Linn, J., "Generic Security Service Application
Program Interface Version 2, Update 1", RFC 2743,
January 2000.
[RFC3125] Ross, J., Pinkas, D., and N. Pope, "Electronic
Signature Policies", RFC 3125, September 2001.
[RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography
Standards (PKCS) #1: RSA Cryptography Specifications
Version 2.1", RFC 3447, February 2003.
[RFC3494] Zeilenga, K., "Lightweight Directory Access Protocol
version 2 (LDAPv2) to Historic Status", RFC 3494,
March 2003.
[RFC3851] Ramsdell, B., Ed., "Secure/Multipurpose Internet Mail
Extensions (S/MIME) Version 3.1 Message
Specification", RFC 3851, July 2004.
[RFC4210] Adams, C., Farrell, S., Kause, T., and T. Mononen,
"Internet X.509 Public Key Infrastructure Certificate
Management Protocol (CMP)", RFC 4210, September 2005.
[RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer
Security (TLS) Protocol Version 1.1", RFC 4346, April
2006.
[RFC4523] Zeilenga, K., "Lightweight Directory Access Protocol
(LDAP) Schema Definitions for X.509 Certificates", RFC
4523, June 2006.
Pinkas, et al. Informational [Page 66]RFC 5126 CMS Advanced Electronic Signatures February 2008
[ISO7498-2] ISO 7498-2 (1989): "Information processing systems -
Open Systems Interconnection - Basic Reference Model -
Part 2: Security Architecture".
[ISO9796-2] ISO/IEC 9796-2 (2002): "Information technology -
Security techniques - Digital signature schemes giving
message recovery - Part 2: Integer factorization based
mechanisms".
[ISO9796-4] ISO/IEC 9796-4 (1998): "Digital signature schemes
giving message recovery - Part 4: Discrete logarithm
based mechanisms".
[ISO10118-1] ISO/IEC 10118-1 (2000): "Information technology -
Security techniques - Hash-functions - Part 1:
General".
[ISO10118-2] ISO/IEC 10118-2 (2000): "Information technology -
Security techniques - Hash-functions - Part 2:
Hash-functions using an n-bit block cipher algorithm".
[ISO10118-3] ISO/IEC 10118-3 (2004): "Information technology -
Security techniques - Hash-functions - Part 3:
Dedicated hash-functions".
[ISO10118-4] ISO/IEC 10118-4 (1998): "Information technology -
Security techniques - Hash-functions - Part 4: Hash-
functions using modular arithmetic".
[ISO10181-5] ISO/IEC 10181-5: Security Frameworks in Open Systems.
Non-Repudiation Framework. April 1997.
[ISO13888-1] ISO/IEC 13888-1 (2004): "IT security techniques -
Non-repudiation - Part 1: General".
[ISO14888-1] ISO/IEC 14888-1 (1998): "Information technology -
Security techniques - Digital signatures with appendix
- Part 1: General".
[ISO14888-2] ISO/IEC 14888-2 (1999): "Information technology -
Security techniques - Digital signatures with appendix
- Part 2: Identity-based mechanisms".
[ISO14888-3] ISO/IEC 14888-3 (1998): "Information technology -
Security techniques - Digital signatures with appendix
- Part 3: Certificate-based mechanisms".
Pinkas, et al. Informational [Page 67]RFC 5126 CMS Advanced Electronic Signatures February 2008
[ISO15946-2] ISO/IEC 15946-2 (2002): "Information technology -
Security techniques - Cryptographic techniques based
on elliptic curves - Part 2: Digital signatures".
[CWA14171] CWA 14171 CEN Workshop Agreement: "General Guidelines
for Electronic Signature Verification".
[XMLDSIG] XMLDSIG: W3C/IETF Recommendation (February 2002):
"XML-Signature Syntax and Processing".
[X9.30-1] ANSI X9.30-1 (1997): "Public Key Cryptography for the
Financial Services Industry - Part 1: The Digital
Signature Algorithm (DSA)".
[X9.30-2] ANSI X9.30-2 (1997): "Public Key Cryptography for the
Financial Services Industry - Part 2: The Secure Hash
Algorithm (SHA-1)".
[X9.31-1] ANSI X9.31-1 (1997): "Public Key Cryptography Using
Reversible Algorithms for the Financial Services
Industry - Part 1: The RSA Signature Algorithm".
[X9.31-2] ANSI X9.31-2 (1996): "Public Key Cryptography Using
Reversible Algorithms for the Financial Services
Industry - Part 2: Hash Algorithms".
[X9.62] ANSI X9.62 (1998): "Public Key Cryptography for the
Financial Services Industry - The Elliptic Curve
Digital Signature Algorithm (ECDSA)".
[P1363] IEEE P1363 (2000): "Standard Specifications for
Public-Key Cryptography".
ETSI technical specifications can be downloaded free of charge via
the Services and Products Download Area at:
http://www.etsi.org/WebSite/Standards/StandardsDownload.aspx
Pinkas, et al. Informational [Page 68]RFC 5126 CMS Advanced Electronic Signatures February 2008
Annex A (Normative): ASN.1 Definitions
This annex provides a summary of all the ASN.1 syntax definitions for
new syntax defined in the present document.
A.1. Signature Format Definitions Using X.208 ASN.1 Syntax
NOTE: The ASN.1 module defined in Annex A.1 using syntax defined
in ITU-T Recommendation X.208 [14] has precedence over that
defined in Annex A.2 in the case of any conflict.
ETS-ElectronicSignatureFormats-ExplicitSyntax88 { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-mod(0)
eSignature-explicit88(28)}
DEFINITIONS EXPLICIT TAGS ::=
BEGIN
-- EXPORTS All
IMPORTS
-- Cryptographic Message Syntax (CMS): RFC 3852
ContentInfo, ContentType, id-data, id-signedData, SignedData,
EncapsulatedContentInfo, SignerInfo, id-contentType,
id-messageDigest, MessageDigest, id-signingTime, SigningTime,
id-countersignature, Countersignature
FROM CryptographicMessageSyntax2004
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) modules(0) cms-2004(24) }
-- ESS Defined attributes: ESS Update
-- RFC 5035 (Adding CertID Algorithm Agility)
id-aa-signingCertificate, SigningCertificate, IssuerSerial,
id-aa-contentReference, ContentReference, id-aa-contentIdentifier,
ContentIdentifier, id-aa-signingCertificateV2
FROM ExtendedSecurityServices-2006
{ iso(1) member-body(2) us(840) rsadsi(113549)
pkcs(1) pkcs-9(9) smime(16) modules(0) id-mod-ess-2006(30) }
-- Internet X.509 Public Key Infrastructure - Certificate and CRL
-- Profile: RFC 3280
Certificate, AlgorithmIdentifier, CertificateList, Name,
DirectoryString, Attribute, BMPString, UTF8String
Pinkas, et al. Informational [Page 69]RFC 5126 CMS Advanced Electronic Signatures February 2008
FROM PKIX1Explicit88
{iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0) id-pkix1-explicit(18)}
GeneralNames, GeneralName, PolicyInformation
FROM PKIX1Implicit88
{iso(1) identified-organization(3) dod(6) internet(1) security(5)
mechanisms(5) pkix(7) id-mod(0) id-pkix1-implicit (19)}
-- Internet Attribute Certificate Profile for Authorization - RFC 3281
AttributeCertificate
FROM PKIXAttributeCertificate {iso(1) identified-organization(3)
dod(6) internet(1) security(5) mechanisms(5) pkix(7)
id-mod(0) id-mod-attribute-cert(12)}
-- OCSP - RFC 2560
BasicOCSPResponse, ResponderID
FROM OCSP {iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-ocsp(14)}
-- Time Stamp Protocol RFC 3161
TimeStampToken
FROM PKIXTSP
{iso(1) identified-organization(3) dod(6) internet(1) security(5)
mechanisms(5) pkix(7) id-mod(0) id-mod-tsp(13)}
;
-- Definitions of Object Identifier arcs used in the present document
-- ==================================================================
-- OID used referencing electronic signature mechanisms based on
-- the present document for use with the Independent Data Unit
-- Protection (IDUP) API (see Annex D)
id-etsi-es-IDUP-Mechanism-v1 OBJECT IDENTIFIER ::=
{ itu-t(0) identified-organization(4) etsi(0)
electronic-signature-standard (1733) part1 (1) idupMechanism (4)
etsiESv1(1) }
-- Basic ES CMS Attributes Defined in the present document
-- =======================================================
Pinkas, et al. Informational [Page 70]RFC 5126 CMS Advanced Electronic Signatures February 2008
-- OtherSigningCertificate - deprecated
id-aa-ets-otherSigCert OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 19 }
OtherSigningCertificate ::= SEQUENCE {
certs SEQUENCE OF OtherCertID,
policies SEQUENCE OF PolicyInformation OPTIONAL
-- NOT USED IN THE PRESENT DOCUMENT
}
OtherCertID ::= SEQUENCE {
otherCertHash OtherHash,
issuerSerial IssuerSerial OPTIONAL }
OtherHash ::= CHOICE {
sha1Hash OtherHashValue,
-- This contains a SHA-1 hash
otherHash OtherHashAlgAndValue}
-- Policy ES Attributes Defined in the present document
-- ====================================================
-- Mandatory Basic Electronic Signature Attributes as above,
-- plus in addition.
-- Signature-policy-identifier attribute
id-aa-ets-sigPolicyId OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 15 }
SignaturePolicy ::= CHOICE {
signaturePolicyId SignaturePolicyId,
signaturePolicyImplied SignaturePolicyImplied
-- not used in this version
}
SignaturePolicyId ::= SEQUENCE {
sigPolicyId SigPolicyId,
sigPolicyHash SigPolicyHash,
sigPolicyQualifiers SEQUENCE SIZE (1..MAX) OF
SigPolicyQualifierInfo OPTIONAL
}
SignaturePolicyImplied ::= NULL
Pinkas, et al. Informational [Page 71]RFC 5126 CMS Advanced Electronic Signatures February 2008
SigPolicyId ::= OBJECT IDENTIFIER
SigPolicyHash ::= OtherHashAlgAndValue
OtherHashAlgAndValue ::= SEQUENCE {
hashAlgorithm AlgorithmIdentifier,
hashValue OtherHashValue }
OtherHashValue ::= OCTET STRING
SigPolicyQualifierInfo ::= SEQUENCE {
sigPolicyQualifierId SigPolicyQualifierId,
sigQualifier ANY DEFINED BY sigPolicyQualifierId }
SigPolicyQualifierId ::= OBJECT IDENTIFIER
id-spq-ets-uri OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-spq(5) 1 }
SPuri ::= IA5String
id-spq-ets-unotice OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-spq(5) 2 }
SPUserNotice ::= SEQUENCE {
noticeRef NoticeReference OPTIONAL,
explicitText DisplayText OPTIONAL}
NoticeReference ::= SEQUENCE {
organization DisplayText,
noticeNumbers SEQUENCE OF INTEGER }
DisplayText ::= CHOICE {
visibleString VisibleString (SIZE (1..200)),
bmpString BMPString (SIZE (1..200)),
utf8String UTF8String (SIZE (1..200)) }
-- Optional Electronic Signature Attributes
-- Commitment-type attribute
id-aa-ets-commitmentType OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 16}
CommitmentTypeIndication ::= SEQUENCE {
Pinkas, et al. Informational [Page 72]RFC 5126 CMS Advanced Electronic Signatures February 2008
commitmentTypeId CommitmentTypeIdentifier,
commitmentTypeQualifier SEQUENCE SIZE (1..MAX) OF
CommitmentTypeQualifier OPTIONAL}
CommitmentTypeIdentifier ::= OBJECT IDENTIFIER
CommitmentTypeQualifier ::= SEQUENCE {
commitmentTypeIdentifier CommitmentTypeIdentifier,
qualifier ANY DEFINED BY commitmentTypeIdentifier }
id-cti-ets-proofOfOrigin OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 1}
id-cti-ets-proofOfReceipt OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 2}
id-cti-ets-proofOfDelivery OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) cti(6) 3}
id-cti-ets-proofOfSender OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 4}
id-cti-ets-proofOfApproval OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) cti(6) 5}
id-cti-ets-proofOfCreation OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) cti(6) 6}
-- Signer-location attribute
id-aa-ets-signerLocation OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 17}
SignerLocation ::= SEQUENCE {
-- at least one of the following shall be present
countryName [0] DirectoryString OPTIONAL,
-- As used to name a Country in X.500
localityName [1] DirectoryString OPTIONAL,
-- As used to name a locality in X.500
postalAdddress [2] PostalAddress OPTIONAL }
PostalAddress ::= SEQUENCE SIZE(1..6) OF DirectoryString
-- Signer-attributes attribute
Pinkas, et al. Informational [Page 73]RFC 5126 CMS Advanced Electronic Signatures February 2008
id-aa-ets-signerAttr OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 18}
SignerAttribute ::= SEQUENCE OF CHOICE {
claimedAttributes [0] ClaimedAttributes,
certifiedAttributes [1] CertifiedAttributes }
ClaimedAttributes ::= SEQUENCE OF Attribute
CertifiedAttributes ::= AttributeCertificate
-- as defined in RFC 3281: see Section 4.1
-- Content-time-stamp attribute
id-aa-ets-contentTimestamp OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 20}
ContentTimestamp ::= TimeStampToken
-- Signature-time-stamp attribute
id-aa-signatureTimeStampToken OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 14}
SignatureTimeStampToken ::= TimeStampToken
-- Complete-certificate-references attribute
id-aa-ets-certificateRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 21}
CompleteCertificateRefs ::= SEQUENCE OF OtherCertID
-- Complete-revocation-references attribute
id-aa-ets-revocationRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 22}
CompleteRevocationRefs ::= SEQUENCE OF CrlOcspRef
CrlOcspRef ::= SEQUENCE {
crlids [0] CRLListID OPTIONAL,
ocspids [1] OcspListID OPTIONAL,
otherRev [2] OtherRevRefs OPTIONAL
}
Pinkas, et al. Informational [Page 74]RFC 5126 CMS Advanced Electronic Signatures February 2008
CRLListID ::= SEQUENCE {
crls SEQUENCE OF CrlValidatedID}
CrlValidatedID ::= SEQUENCE {
crlHash OtherHash,
crlIdentifier CrlIdentifier OPTIONAL}
CrlIdentifier ::= SEQUENCE {
crlissuer Name,
crlIssuedTime UTCTime,
crlNumber INTEGER OPTIONAL }
OcspListID ::= SEQUENCE {
ocspResponses SEQUENCE OF OcspResponsesID}
OcspResponsesID ::= SEQUENCE {
ocspIdentifier OcspIdentifier,
ocspRepHash OtherHash OPTIONAL
}
OcspIdentifier ::= SEQUENCE {
ocspResponderID ResponderID,
-- As in OCSP response data
producedAt GeneralizedTime
-- As in OCSP response data
}
OtherRevRefs ::= SEQUENCE {
otherRevRefType OtherRevRefType,
otherRevRefs ANY DEFINED BY otherRevRefType
}
OtherRevRefType ::= OBJECT IDENTIFIER
-- Certificate-values attribute
id-aa-ets-certValues OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 23}
CertificateValues ::= SEQUENCE OF Certificate
-- Certificate-revocation-values attribute
id-aa-ets-revocationValues OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 24}
RevocationValues ::= SEQUENCE {
Pinkas, et al. Informational [Page 75]RFC 5126 CMS Advanced Electronic Signatures February 2008
crlVals [0] SEQUENCE OF CertificateList OPTIONAL,
ocspVals [1] SEQUENCE OF BasicOCSPResponse OPTIONAL,
otherRevVals [2] OtherRevVals OPTIONAL}
OtherRevVals ::= SEQUENCE {
otherRevValType OtherRevValType,
otherRevVals ANY DEFINED BY otherRevValType
}
OtherRevValType ::= OBJECT IDENTIFIER
-- CAdES-C time-stamp attribute
id-aa-ets-escTimeStamp OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 25}
ESCTimeStampToken ::= TimeStampToken
-- Time-Stamped Certificates and CRLs
id-aa-ets-certCRLTimestamp OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 26}
TimestampedCertsCRLs ::= TimeStampToken
-- Archive time-stamp attribute
id-aa-ets-archiveTimestampV2 OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 48}
ArchiveTimeStampToken ::= TimeStampToken
-- Attribute-certificate-references attribute
id-aa-ets-attrCertificateRefs OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 44}
AttributeCertificateRefs ::= SEQUENCE OF OtherCertID
-- Attribute-revocation-references attribute
id-aa-ets-attrRevocationRefs OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 45}
AttributeRevocationRefs ::= SEQUENCE OF CrlOcspRef
Pinkas, et al. Informational [Page 76]RFC 5126 CMS Advanced Electronic Signatures February 2008
END
A.2. Signature Format Definitions Using X.680 ASN.1 Syntax
NOTE: The ASN.1 module defined in Annex A.1 has precedence over
that defined in Annex A.2 using syntax defined in ITU-T
Recommendation X.680 (1997) [8] in the case of any conflict.
ETS-ElectronicSignatureFormats-ExplicitSyntax97 { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-mod(0)
eSignature-explicit97(29)}
DEFINITIONS EXPLICIT TAGS ::=
BEGIN
-- EXPORTS All -
IMPORTS
-- Cryptographic Message Syntax (CMS): RFC 3852
ContentInfo, ContentType, id-data, id-signedData, SignedData,
EncapsulatedContentInfo, SignerInfo,
id-contentType, id-messageDigest, MessageDigest, id-signingTime,
SigningTime, id-countersignature, Countersignature
FROM CryptographicMessageSyntax2004
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) modules(0) cms-2004(24) }
-- ESS Defined attributes: ESS Update
-- RFC 5035 (Adding CertID Algorithm Agility)
id-aa-signingCertificate, SigningCertificate, IssuerSerial,
id-aa-contentReference, ContentReference, id-aa-contentIdentifier,
ContentIdentifier, id-aa-signingCertificateV2
FROM ExtendedSecurityServices-2006
{ iso(1) member-body(2) us(840) rsadsi(113549)
pkcs(1) pkcs-9(9) smime(16) modules(0) id-mod-ess-2006(30) }
-- Internet X.509 Public Key Infrastructure
-- Certificate and CRL Profile: RFC 3280
Certificate, AlgorithmIdentifier, CertificateList, Name,
Attribute
FROM PKIX1Explicit88
{iso(1) identified-organization(3) dod(6) internet(1)
Pinkas, et al. Informational [Page 77]RFC 5126 CMS Advanced Electronic Signatures February 2008
security(5) mechanisms(5) pkix(7) id-mod(0)
id-pkix1-explicit(18)}
GeneralNames, GeneralName, PolicyInformation
FROM PKIX1Implicit88 {iso(1) identified-organization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
id-pkix1-implicit(19)}
-- Internet Attribute Certificate Profile for Authorization - RFC 3281
AttributeCertificate
FROM PKIXAttributeCertificate {iso(1) identified-organization(3)
dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-attribute-cert(12)}
-- OCSP RFC 2560
BasicOCSPResponse, ResponderID
FROM OCSP {iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-ocsp(14)}
-- RFC 3161 Internet X.509 Public Key Infrastructure
-- Time-Stamp Protocol
TimeStampToken
FROM PKIXTSP {iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-tsp(13)}
-- X.520
DirectoryString {}
FROM SelectedAttributeTypes
{joint-iso-itu-t ds(5) module(1) selectedAttributeTypes(5) 4}
;
-- Definitions of Object Identifier arcs used in the present document
-- ==================================================================
-- OID used referencing electronic signature mechanisms based
-- on the present document for use with the IDUP API (see Annex D)
id-etsi-es-IDUP-Mechanism-v1 OBJECT IDENTIFIER ::=
{ itu-t(0) identified-organization(4) etsi(0)
electronic-signature-standard (1733) part1 (1) idupMechanism (4)
etsiESv1(1) }
Pinkas, et al. Informational [Page 78]RFC 5126 CMS Advanced Electronic Signatures February 2008
-- Basic ES Attributes Defined in the present document
-- ===================================================
-- CMS Attributes defined in the present document
-- OtherSigningCertificate - deprecated
id-aa-ets-otherSigCert OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 19 }
OtherSigningCertificate ::= SEQUENCE {
certs SEQUENCE OF OtherCertID,
policies SEQUENCE OF PolicyInformation OPTIONAL
-- NOT USED IN THE PRESENT DOCUMENT
}
OtherCertID ::= SEQUENCE {
otherCertHash OtherHash,
issuerSerial IssuerSerial OPTIONAL }
OtherHash ::= CHOICE {
sha1Hash OtherHashValue,
-- This contains a SHA-1 hash
otherHash OtherHashAlgAndValue}
-- Policy ES Attributes Defined in the present document
-- ====================================================
-- Mandatory Basic Electronic Signature Attributes, plus in addition.
-- Signature Policy Identifier
id-aa-ets-sigPolicyId OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 15 }
SignaturePolicy ::= CHOICE {
signaturePolicyId SignaturePolicyId,
signaturePolicyImplied SignaturePolicyImplied
-- not used in this version
}
SignaturePolicyId ::= SEQUENCE {
sigPolicyId SigPolicyId,
sigPolicyHash SigPolicyHash,
sigPolicyQualifiers SEQUENCE SIZE (1..MAX) OF
SigPolicyQualifierInfo OPTIONAL
Pinkas, et al. Informational [Page 79]RFC 5126 CMS Advanced Electronic Signatures February 2008
}
SignaturePolicyImplied ::= NULL
SigPolicyId ::= OBJECT IDENTIFIER
SigPolicyHash ::= OtherHashAlgAndValue
OtherHashAlgAndValue ::= SEQUENCE {
hashAlgorithm AlgorithmIdentifier,
hashValue OtherHashValue
}
OtherHashValue ::= OCTET STRING
SigPolicyQualifierInfo ::= SEQUENCE {
sigPolicyQualifierId SIG-POLICY-QUALIFIER.&id
({SupportedSigPolicyQualifiers}),
qualifier SIG-POLICY-QUALIFIER.&Qualifier
({SupportedSigPolicyQualifiers}
{@sigPolicyQualifierId})OPTIONAL }
SupportedSigPolicyQualifiers SIG-POLICY-QUALIFIER ::=
{ noticeToUser | pointerToSigPolSpec }
SIG-POLICY-QUALIFIER ::= CLASS {
&id OBJECT IDENTIFIER UNIQUE,
&Qualifier OPTIONAL }
WITH SYNTAX {
SIG-POLICY-QUALIFIER-ID &id
[SIG-QUALIFIER-TYPE &Qualifier] }
noticeToUser SIG-POLICY-QUALIFIER ::= {
SIG-POLICY-QUALIFIER-ID id-spq-ets-unotice SIG-QUALIFIER-TYPE
SPUserNotice }
pointerToSigPolSpec SIG-POLICY-QUALIFIER ::= {
SIG-POLICY-QUALIFIER-ID id-spq-ets-uri SIG-QUALIFIER-TYPE SPuri }
id-spq-ets-uri OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-spq(5) 1 }
SPuri ::= IA5String
id-spq-ets-unotice OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-spq(5) 2 }
Pinkas, et al. Informational [Page 80]RFC 5126 CMS Advanced Electronic Signatures February 2008
SPUserNotice ::= SEQUENCE {
noticeRef NoticeReference OPTIONAL,
explicitText DisplayText OPTIONAL}
NoticeReference ::= SEQUENCE {
organization DisplayText,
noticeNumbers SEQUENCE OF INTEGER }
DisplayText ::= CHOICE {
visibleString VisibleString (SIZE (1..200)),
bmpString BMPString (SIZE (1..200)),
utf8String UTF8String (SIZE (1..200)) }
-- Optional Electronic Signature Attributes
-- Commitment Type
id-aa-ets-commitmentType OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 16}
CommitmentTypeIndication ::= SEQUENCE {
commitmentTypeId CommitmentTypeIdentifier,
commitmentTypeQualifier SEQUENCE SIZE (1..MAX) OF
CommitmentTypeQualifier OPTIONAL}
CommitmentTypeIdentifier ::= OBJECT IDENTIFIER
CommitmentTypeQualifier ::= SEQUENCE {
commitmentQualifierId COMMITMENT-QUALIFIER.&id,
qualifier COMMITMENT-QUALIFIER.&Qualifier OPTIONAL }
COMMITMENT-QUALIFIER ::= CLASS {
&id OBJECT IDENTIFIER UNIQUE,
&Qualifier OPTIONAL }
WITH SYNTAX {
COMMITMENT-QUALIFIER-ID &id
[COMMITMENT-TYPE &Qualifier] }
id-cti-ets-proofOfOrigin OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 1}
id-cti-ets-proofOfReceipt OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 2}
id-cti-ets-proofOfDelivery OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
cti(6) 3}
Pinkas, et al. Informational [Page 81]RFC 5126 CMS Advanced Electronic Signatures February 2008
id-cti-ets-proofOfSender OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 4}
id-cti-ets-proofOfApproval OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) cti(6) 5}
id-cti-ets-proofOfCreation OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) cti(6) 6}
-- Signer Location
id-aa-ets-signerLocation OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 17}
SignerLocation ::= SEQUENCE {
-- at least one of the following shall be present
countryName [0] DirectoryString{maxSize} OPTIONAL,
-- as used to name a Country in X.520
localityName [1] DirectoryString{maxSize} OPTIONAL,
-- as used to name a locality in X.520
postalAdddress [2] PostalAddress OPTIONAL }
PostalAddress ::= SEQUENCE SIZE(1..6) OF DirectoryString{maxSize}
-- maxSize parametrization as specified in X.683
-- Signer Attributes
id-aa-ets-signerAttr OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 18}
SignerAttribute ::= SEQUENCE OF CHOICE {
claimedAttributes [0] ClaimedAttributes,
certifiedAttributes [1] CertifiedAttributes }
ClaimedAttributes ::= SEQUENCE OF Attribute
CertifiedAttributes ::= AttributeCertificate
-- as defined in RFC 3281: see Section 4.1
-- Content Timestamp
id-aa-ets-contentTimestamp OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 20}
ContentTimestamp ::= TimeStampToken
Pinkas, et al. Informational [Page 82]RFC 5126 CMS Advanced Electronic Signatures February 2008
-- Signature Timestamp
id-aa-signatureTimeStampToken OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 14}
SignatureTimeStampToken ::= TimeStampToken
-- Complete Certificate Refs.
id-aa-ets-certificateRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 21}
CompleteCertificateRefs ::= SEQUENCE OF OtherCertID
-- Complete Revocation Refs
id-aa-ets-revocationRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 22}
CompleteRevocationRefs ::= SEQUENCE OF CrlOcspRef
CrlOcspRef ::= SEQUENCE {
crlids [0] CRLListID OPTIONAL,
ocspids [1] OcspListID OPTIONAL,
otherRev [2] OtherRevRefs OPTIONAL
}
CRLListID ::= SEQUENCE {
crls SEQUENCE OF CrlValidatedID
}
CrlValidatedID ::= SEQUENCE {
crlHash OtherHash,
crlIdentifier CrlIdentifier OPTIONAL }
CrlIdentifier ::= SEQUENCE {
crlissuer Name,
crlIssuedTime UTCTime,
crlNumber INTEGER OPTIONAL
}
OcspListID ::= SEQUENCE {
ocspResponses SEQUENCE OF OcspResponsesID
}
OcspResponsesID ::= SEQUENCE {
ocspIdentifier OcspIdentifier,
Pinkas, et al. Informational [Page 83]RFC 5126 CMS Advanced Electronic Signatures February 2008
ocspRepHash OtherHash OPTIONAL
}
OcspIdentifier ::= SEQUENCE {
ocspResponderID ResponderID,
-- As in OCSP response data
producedAt GeneralizedTime
-- As in OCSP response data
}
OtherRevRefs ::= SEQUENCE {
otherRevRefType OTHER-REVOCATION-REF.&id,
otherRevRefs SEQUENCE OF OTHER-REVOCATION-REF.&Type
}
OTHER-REVOCATION-REF ::= CLASS {
&Type,
&id OBJECT IDENTIFIER UNIQUE }
WITH SYNTAX {
WITH SYNTAX &Type ID &id }
-- Certificate Values
id-aa-ets-certValues OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 23}
CertificateValues ::= SEQUENCE OF Certificate
-- Certificate Revocation Values
id-aa-ets-revocationValues OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 24}
RevocationValues ::= SEQUENCE {
crlVals [0] SEQUENCE OF CertificateList OPTIONAL,
ocspVals [1] SEQUENCE OF BasicOCSPResponse OPTIONAL,
otherRevVals [2] OtherRevVals OPTIONAL
}
OtherRevVals ::= SEQUENCE {
otherRevValType OTHER-REVOCATION-VAL.&id,
otherRevVals SEQUENCE OF OTHER-REVOCATION-REF.&Type
}
OTHER-REVOCATION-VAL ::= CLASS {
&Type,
Pinkas, et al. Informational [Page 84]RFC 5126 CMS Advanced Electronic Signatures February 2008
&id OBJECT IDENTIFIER UNIQUE }
WITH SYNTAX {
WITH SYNTAX &Type ID &id }
-- CAdES-C Timestamp
id-aa-ets-escTimeStamp OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 25}
ESCTimeStampToken ::= TimeStampToken
-- Time-Stamped Certificates and CRLs
id-aa-ets-certCRLTimestamp OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 26}
TimestampedCertsCRLs ::= TimeStampToken
-- Archive Timestamp
id-aa-ets-archiveTimestampV2 OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 48}
ArchiveTimeStampToken ::= TimeStampToken
-- Attribute certificate references
id-aa-ets-attrCertificateRefs OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 44}
AttributeCertificateRefs ::= SEQUENCE OF OtherCertID
-- Attribute revocation references
id-aa-ets-attrRevocationRefs OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 45}
AttributeRevocationRefs ::= SEQUENCE OF CrlOcspRef
END
Pinkas, et al. Informational [Page 85]RFC 5126 CMS Advanced Electronic Signatures February 2008
Annex B (Informative): Extended Forms of Electronic Signatures
Section 4 provides an overview of the various formats of electronic
signatures included in the present document. This annex lists the
attributes that need to be present in the various extended electronic
signature formats and provides example validation sequences using the
extended formats.
B.1. Extended Forms of Validation Data
The Complete validation data (CAdES-C) described in Section 4.3 and
illustrated in Figure 3 may be extended to create electronic
signatures with extended validation data. Some electronic signature
forms that include extended validation are explained below.
An X-Long electronic signature (CAdES-X Long) is the CAdES-C with the
values of the certificates and revocation information.
This form of electronic signature can be useful when the verifier
does not have direct access to the following information:
- the signer's certificate;
- all the CA certificates that make up the full certification
path;
- all the associated revocation status information, as referenced
in the CAdES-C.
In some situations, additional time-stamps may be created and added
to the Electronic Signatures as additional attributes. For example:
- time-stamping all the validation data as held with the ES
(CAdES-C), this eXtended validation data is called a CAdES-X
Type 1; or
- time-stamping individual reference data as used for complete
validation. This form of eXtended validation data is called an
CAdES-X Type 2.
NOTE 1: The advantages/drawbacks for CAdES-X Type 1 and CAdES-X
Type 2 are discussed in Annex C.4.4.
The above time-stamp forms can be useful when it is required to
counter the risk that any CA keys used in the certificate chain may
be compromised.
Pinkas, et al. Informational [Page 86]RFC 5126 CMS Advanced Electronic Signatures February 2008
A combination of the two formats above may be used. This form of
eXtended validation data is called an ES X-Long Type 1 or CAdES-X
Long Type 2. This form of electronic signature can be useful when
the verifier needs both the values and proof of when the validation
data existed.
NOTE 2: The advantages/drawbacks for CAdES-X long Type 1 and
CAdES-X long Type 2 are discussed in Annex C.4.6.
B.1.1. CAdES-X Long
An electronic signature with the additional validation data forming
the CAdES-X Long form (CAdES-X-Long) is illustrated in Figure B.1 and
comprises the following:
- CAdES-BES or CAdES-EPES, as defined in Sections 4.3 , 5.7, or
5.8;
- complete-certificate-references attribute, as defined in Section
6.2.1;
- complete-revocation-references attribute, as defined in Section
6.2.2.
The following attributes are required if a TSP is not providing a
time-mark of the ES:
- signature-time-stamp attribute, as defined in Section 6.1.1.
The following attributes are required if the full certificate values
and revocation values are not already included in the CAdES-BES or
CAdES-EPES:
- certificate-values attribute, as defined in Section 6.3.3;
- revocation-values attribute, as defined in Section 6.3.4.
If attributes certificates are used, then the following attributes
may be present:
- attribute-certificate-references attribute, defined in Section
6.2.3;
- attribute-revocation-references attribute, as defined in Section
6.2.4.
Other unsigned attributes may be present, but are not required.
Pinkas, et al. Informational [Page 87]RFC 5126 CMS Advanced Electronic Signatures February 2008
NOTE: Attribute certificate and revocation references are only
present if a user attribute certificate is present in the
electronic signature; see Sections 6.2.2 and 6.2.3.
+---------------------- CAdES-X-Long --------------------------------+
|+-------------------------------------- CAdES-C ---+ |
|| +----------+ | +-------------+|
||+----- CAdES-BES or CAdES-EPES ----+ |Timestamp | | | ||
||| | |over | | | Complete ||
|||+---------++----------++---------+| |digital | | | certificate ||
|||| || || || |signature | | | and ||
||||Signer's || Signed ||Digital || | | | | revocation ||
||||Document ||Attributes||signature|| |Optional | | | data ||
|||| || || || |when | | | ||
|||+---------++----------++---------+| |timemarked| | | ||
||+----------------------------------+ +----------+ | | ||
|| +-----------+| +-------------+|
|| |Complete || |
|| |certificate|| |
|| |and || |
|| |revocation || |
|| |references || |
|| +-----------+| |
|+--------------------------------------------------+ |
| |
+--------------------------------------------------------------------+
Figure B.1: Illustration of CAdES-X-Long
B.1.2. CAdES-X Type 1
An electronic signature with the additional validation data forming
the eXtended validation data - Type 1 X is illustrated in Figure B.2
and comprises the following:
- the CAdES-BES or CAdES-EPES, as defined in Sections 4.2, 5.7, or
5.8;
- complete-certificate-references attribute, as defined in Section
6.2.1;
- complete-revocation-references attribute, as defined in Section
6.2.2;
- CAdES-C-Timestamp attribute, as defined in Section 6.3.5.
Pinkas, et al. Informational [Page 88]RFC 5126 CMS Advanced Electronic Signatures February 2008
The following attributes are required if a TSP is not providing a
time-mark of the ES:
- signature-time-stamp attribute, as defined in Section 6.1.1.
If attributes certificates are used, then the following attributes
may be present:
- attribute-certificate-references attribute, defined in Section
6.2.3;
- attribute-revocation-references attribute, as defined in Section
6.2.4.
Other unsigned attributes may be present, but are not required.
+------------------------ CAdES-X-Type 1 ----------------------------+
|+---------------------------------- CAdES-C ------+ |
|| +----------+ | +-------------+ |
||+--- CAdES-BES or CAdES-EPES ------+|Timestamp | | | | |
||| ||over | | | | |
|||+---------++----------++---------+||digital | | | | |
||||Signer's || Signed || Digital |||signature | | | Timestamp | |
||||Document ||Attributes||signature||| | | | over | |
|||| || || |||Optional | | | CAdES-C | |
|||+---------++----------++---------+||when | | | | |
||+----------------------------------+|timemarked| | | | |
|| +----------+ | | | |
|| +-----------+| +-------------+ |
|| |Complete || |
|| |certificate|| |
|| | and || |
|| |revocation || |
|| |references || |
|| +-----------+| |
|+-------------------------------------------------+ |
| |
+--------------------------------------------------------------------+
Figure B.2: Illustration of CAdES-X Type 1
Pinkas, et al. Informational [Page 89]RFC 5126 CMS Advanced Electronic Signatures February 2008
B.1.3. CAdES-X Type 2
An electronic signature with the additional validation data forming
the eXtended Validation Data - Type 2 X is illustrated in Figure B.3
and comprises the following:
- CAdES-BES or CAdES-EPES, as defined in Sections 4.2, 5.7, or
5.8;
- complete-certificate-references attribute, as defined in Section
6.2.1;
- complete-revocation-references attribute, as defined in Section
6.2.2;
- time-stamped-certs-crls-references attribute, as defined in
Section 6.3.6.
The following attributes are required if a TSP is not providing a
time-mark of the ES:
- signature-time-stamp attribute, as defined in Section 6.1.1.
If attributes certificates are used, then the following attributes
may be present:
- attribute-certificate-references attribute, defined in Section
6.2.3;
- attribute-revocation-references attribute, as defined in Section
6.2.4.
Other unsigned attributes may be present, but are not required.
Pinkas, et al. Informational [Page 90]RFC 5126 CMS Advanced Electronic Signatures February 2008
+----------------------- CAdES-X-Type 2 -----------------------------+
|+-------------------------------------- CAdES-C --+ |
|| +----------+ | |
||+-- CAdES-BES or CAdES-EPES -------+|Timestamp | | |
||| ||over | | |
|||+---------++----------++---------+||digital | | +-------------+ |
|||| || || |||Signature | | | Timestamp | |
||||Signer's || Signed || Digital ||| | | | only over | |
||||Document ||Attributes||signature|||Optional | | | Complete | |
|||| || || |||when | | | certificate | |
|||+---------++----------++---------+||Timemarked| | | and | |
||+----------------------------------++----------+ | | revocation | |
|| +-----------+| | references | |
|| |Complete || +-------------+ |
|| |certificate|| |
|| |and || |
|| |revocation || |
|| |references || |
|| +-----------+| |
|+-------------------------------------------------+ |
| |
+--------------------------------------------------------------------+
Figure B.3: Illustration of CAdES-X Type 2
B.1.4. CAdES-X Long Type 1 and CAdES-X Long Type 2
An electronic signature with the additional validation data forming
the CAdES-X Long Type 1 and CAdES-X Long Type 2 is illustrated in
Figure B.4 and comprises the following:
- CAdES-BES or CAdES-EPES, as defined in Sections 4.3, 5.7, or
5.8;
- complete-certificate-references attribute, as defined in Section
6.2.1;
- complete-revocation-references attribute, as defined in Section
6.2.2;
The following attributes are required if a TSP is not providing a
time-mark of the ES:
- signature-time-stamp attribute, as defined in Section 6.1.1.
Pinkas, et al. Informational [Page 91]RFC 5126 CMS Advanced Electronic Signatures February 2008
The following attributes are required if the full certificate values
and revocation values are not already included in the CAdES-BES or
CAdES-EPES:
- certificate-values attribute, as defined in Section 6.3.3;
- revocation-values attribute, as defined in Section 6.3.4.
If attributes certificates are used, then the following attributes
may be present:
- attribute-certificate-references attribute, defined in Section
6.2.3;
- attribute-revocation-references attribute, as defined in Section
6.2.4.
Plus one of the following attributes is required:
- CAdES-C-Timestamp attribute, as defined in Section 6.3.5;
- time-stamped-certs-crls-references attribute, as defined in
Section 6.3.6.
Other unsigned attributes may be present, but are not required.
Pinkas, et al. Informational [Page 92]RFC 5126 CMS Advanced Electronic Signatures February 2008
+---------------------- CAdES-X-Type 1 or 2 ------------------------+
| +--------------+|
|+-------------------------------------- CAdES-C --+|+------------+||
|| +----------+ ||| Timestamp |||
||+-- CAdES-BES or CAdES-EPES -------+|Timestamp | ||| over |||
||| ||over | ||| CAdES-C |||
|||+---------++----------++---------+||digital | | +------------+ |
|||| || || |||signature | || or ||
||||Signer's || Signed || Digital ||| | ||+------------+||
||||Document ||Attributes||Signature|||Optional | ||| Timestamp |||
|||| || || |||when | ||| only over |||
|||+---------++----------++---------+||timemarked| ||| complete |||
||+----------------------------------++----------+ ||| certificate|||
|| ||| and |||
|| +-----------+||| revocation |||
|| |Complete |||| references |||
|| |certificate|||+------------+||
|| |and ||+--------------+|
|| |revocation || +------------+ |
|| |references || |Complete | |
|| +-----------+| |certificate | |
|+-------------------------------------------------+ | and | |
| |revocation | |
| | values | |
| +------------+ |
+-------------------------------------------------------------------+
Figure B.4: Illustration of CAdES-X Long Type 1
and CAdES-X Long Type 2
B.2. Time-Stamp Extensions
Each instance of the time-stamp attribute may include, as unsigned
attributes in the signedData of the time-stamp, the following
attributes related to the TSU:
- complete-certificate-references attribute of the TSU, as defined
in Section 6.2.1;
- complete-revocation-references attribute of the TSU, as defined
in Section 6.2.2;
- certificate-values attribute of the TSU, as defined in Section
6.3.3;
- revocation-values attribute of the TSU, as defined in Section
6.3.4.
Pinkas, et al. Informational [Page 93]RFC 5126 CMS Advanced Electronic Signatures February 2008
Other unsigned attributes may be present, but are not required.
B.3. Archive Validation Data (CAdES-A)
Before the algorithms, keys, and other cryptographic data used at the
time the CAdES-C was built become weak and the cryptographic
functions become vulnerable, or the certificates supporting previous
time-stamps expire, the signed data, the CAdES-C, and any additional
information (i.e., any CAdES-X) should be time-stamped. If possible,
this should use stronger algorithms (or longer key lengths) than in
the original time-stamp. This additional data and time-stamp is
called Archive validation data required for the ES Archive format
(CAdES-A). The Time-stamping process may be repeated every time the
protection used to time-stamp a previous CAdES-A becomes weak. A
CAdES-A may thus bear multiple embedded time-stamps.
An example of an electronic signature (ES), with the additional
validation data for the CAdES-C and CAdES-X forming the CAdES-A is
illustrated in Figure B.5.
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RFC 5126 CMS Advanced Electronic Signatures February 2008
+--------------------------- CAdES-A---------------------------------+
|+----------------------------------------------------+ |
|| +--------------+| +----------+ |
||+--------------------- CAdES-C ----+|+------------+|| | | |
||| +----------+ ||| Timestamp ||| | | |
|||+-- CAdES-BES ------+|Timestamp | ||| over ||| | | |
|||| or CAdES-EPES ||over | ||| CAdES-C ||| | Archive | |
|||| ||digital | ||+------------+|| | | |
|||| ||signature | || or || |Timestamp | |
|||| || | ||+------------+|| | | |
|||| ||optional | ||| Timestamp ||| | | |
|||| ||when | ||| only over ||| | | |
|||| ||timemarked| ||| complete ||| | | |
|||+-------------------++----------+ ||| certificate||| +----------+ |
||| ||| and ||| |
||| +-------------+||| revocation ||| |
||| | Complete |||| references ||| |
||| | certificate |||+------------+|| |
||| | and ||+--------------+| |
||| | revocation || +------------+ | |
||| | references || |Complete | | |
||| +-------------+| |certificate | | |
||+----------------------------------+ | and | | |
|| |revocation | | |
|| | values | | |
|| +------------+ | |
|+----------------------------------------------------+ |
+--------------------------------------------------------------------+
Figure B.5: Illustration of CAdES-A
The CAdES-A comprises the following elements:
- the CAdES-BES or CAdES-EPES, including their signed and unsigned
attributes;
- complete-certificate-references attribute, as defined in Section
6.2.1;
- complete-revocation-references attribute, as defined in Section
6.2.2.
The following attributes are required if a TSP is not providing a
time-mark of the ES:
- signature-time-stamp attribute, as defined in Section 6.1.1.
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If attributes certificates are used, then the following attributes
may be present:
- attribute-certificate-references attribute, defined in Section
6.2.3;
- attribute-revocation-references attribute, as defined in Section
6.2.4.
The following attributes are required if the full certificate values
and revocation values are not already included in the CAdES-BES or
CAdES-EPES:
- certificate-values attribute, as defined in Section 6.3.3;
- revocation-values attribute, as defined in Section 6.3.4.
At least one of the following two attributes is required:
- CAdES-C-Timestamp attribute, as defined in Section 6.3.5;
- time-stamped-certs-crls-references attribute, as defined in
Section 6.3.6.
The following attribute is required:
- archive-time-stamp attributes, defined in Section 6.4.1.
Several instances of the archive-time-stamp attribute may occur with
an electronic signature, both over time and from different TSUs. The
time-stamp should be created using stronger algorithms (or longer key
lengths) than in the original electronic signatures or time-stamps.
Other unsigned attributes of the ES may be present, but are not
required.
The archive-time-stamp will itself contain the certificate and
revocation information required to validate the archive-time-stamp;
this may include the following unsigned attributes:
- complete-certificate-references attribute of the TSU, as defined
in Section 6.2.1;
- complete-revocation-references attribute of the TSU, as defined
in Section 6.2.2;
- certificate-values attribute of the TSU, as defined in Section
6.3.3;
Pinkas, et al. Informational [Page 96]RFC 5126 CMS Advanced Electronic Signatures February 2008
- revocation-values attribute of the TSU, as defined in Section
6.3.4.
Other unsigned attributes may be present, but are not required.
B.4. Example Validation Sequence
As described earlier, the signer or initial verifier may collect all
the additional data that forms the electronic signature. Figure B.6
and the subsequent description describe how the validation process
may build up a complete electronic signature over time.
+------------------------------------------ CAdES-C -------------+
|+------------------------------- CAdES-T ------+ |
||+-------------- CAdES ------------+ | |
|||+--------------------++---------+|+---------+| +-----------+ |
|||| ________ || |||Timestamp|| |Complete | |
|||||Sign.Pol| ||Digital |||over || |certificate| |
||||| Id. | Signed ||signature|||digital || | and | |
||||| option.|attributes|| |||signature|| |revocation | |
|||||________| |+---------+|+---------+| |references | |
|||+--------------------+ | ^ | +-----------+ |
||+---------------------------------+ | | ^ |
|| 1 | / | | |
|+---------------------- | ------------/--------+ | |
+----------------------- | ---------- / --------------- / -------+
| /2 ----3--------
+----------+ | / /
| | v / |
| Signer's | +---------------------+ +-------------+
| document |----->| Validation Process |---->|- Valid |
| | +---------------------+ 4 |- Invalid |
+----------+ | ^ | ^ |- Validation |
v | v | | Incomplete |
+---------+ +--------+ +-------------+
|Signature| |Trusted |
| Policy | |Service |
| Issuer | |Provider|
+---------+ +--------+
Figure B.6: Illustration of a CAdES validation sequence
Soon after receiving the electronic signature (CAdES) from the signer
(1), the digital signature value may be checked; the validation
process shall at least add a time-stamp (2), unless the signer has
provided one which is trusted by the verifier. The validation
process may also validate the electronic signature using additional
data (e.g., certificates, CRL, etc.) provided by Trusted Service
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Providers. When applicable, the validation process will also need to
conform to the requirements specified in a signature policy. If the
validation process is validation incomplete, then the output from
this stage is the CAdES-T.
To ascertain the validity status as Valid or Invalid and communicate
that to the user (4), all the additional data required to validate
the CAdES-C must be available (e.g., the complete certificate and
revocation information).
Once the data needed to complete validation data references (CAdES-C)
is available, then the validation process should:
- obtain all the necessary additional certificates and revocation
status information;
- complete all the validation checks on the ES using the complete
certificate and revocation information (if a time-stamp is not
already present, this may be added at the same stage, combining
the CAdES-T and CAdES-C processes);
- record the complete certificate and revocation references (3);
- indicate the validity status to the user (4).
At the same time as the validation process creates the CAdES-C, the
validation process may provide and/or record the values of
certificates and revocation status information used in CAdES-C (5).
The end result is called CAdES-X Long.
This is illustrated in Figure B.7.
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+----------------------------------------------------- CAdES-X Long -+
|+------------------------------- CAdES-C -------------+ |
||+-------------- CAdES ------------+ | |
|||+--------------------++---------+|+---------+ |+-----------+|
|||| ________ || |||Timestamp| ||Complete ||
|||||Sign.Pol| ||Digital |||over | ||certificate||
||||| Id. | Signed ||signature|||digital | || and ||
||||| option.|attributes|| |||signature| ||revocation ||
|||||________| || ||+---------+ || values ||
|||+--------------------++---------+| ^ +-----------+|+-----------+|
||+---------------------------------+ | |Complete || ^ |
|| | | |certificate|| | |
|| | 2 | | and || | |
|| | | |revocation || | |
|| | | |references || | |
|| 1 | / +-----------+| | |
|+------------------------ | ------- / --------- ^-----+ / |
+------------------------- | ------ / ---------- |--------- / -------+
| / ----- / ------- /
+----------+ | / / 3 / 5
| | v | | |
| Signer's | +--------------------+ +-----------+
| document |----->| Validation Process |----->| - Valid |
| | +--------------------+ 4 | - Invalid |
+----------+ | ^ | ^ +-----------+
v | v |
+---------+ +--------+
|Signature| |Trusted |
| Policy | |Service |
| Issuer | |Provider|
+---------+ +--------+
Figure B.7: Illustration of a CAdES validation sequence
with CAdES-X Long
When the validation process creates the CAdES-C, it may also create
extended forms of validation data.
A first alternative is to time-stamp all data forming the CAdES-X
Type 1.
This is illustrated in Figure B.8.
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+------------------------------------------------ CAdES-X Type 1 -----+
|+------------------------------- CAdES-C ------------------+ |
||+-------------- CAdES ------------+ | |
|||+--------------------++---------+|+---------++----------+|+-------+|
|||| ________ || |||Timestamp|| Complete ||| ||
|||||Sign.Pol| ||Digital |||over || cert. |||Time- ||
||||| Id. | Signed ||signature|||digital || and |||stamp ||
||||| option.|attributes|| |||signature|| revoc. ||| over ||
|||||________| |+---------+|+---------+|references|||CAdES-C||
|||+--------------------+ | ^ | ||| ||
||+---------------------------------+ | +----------+|+-------+|
|| | | ^ | ^ |
|| 1 | / | | | |
|+------------------------ | --------- / ----------- / -----+ | |
+------------------------- | -------- / ----------- / --------- / ----+
| 2 / ---3---- /
+----------+ | / / -----------5------
| | v | | /
| Signer's | +--------------------+ +-----------+
| document |----->| Validation Process |-----> | - Valid |
| | +--------------------+ 4 | - Invalid |
+----------+ | ^ | ^ +-----------+
v | v |
+---------+ +--------+
|Signature| |Trusted |
| Policy | |Service |
| Issuer | |Provider|
+---------+ +--------+
Figure B.8: Illustration of CAdES with eXtended validation data
CAdES-X Type 1
Another alternative is to time-stamp the certificate and revocation
information references used to validate the electronic signature (but
not the signature) (6). The end result is called CAdES-X Type 2.
This is illustrated in Figure B.9.
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+-------------------------------------------- CAdES-X Type 2 --------+
|+------------------------------- CAdES-C -------------+ |
||+-------------- CAdES ------------+ | |
|||+--------------------++---------+|+---------+ |+-----------+|
|||| ________ || |||Timestamp| ||Timestamp ||
|||||Sign.Pol| || |||over | || over ||
||||| Id. | Signed ||Digital |||digital | ||complete ||
||||| option.|attributes||signature|||signature| ||certificate||
|||||________| || ||| | || ||
|||+--------------------++---------+|+---------+ || and ||
||+---------------------------------+ ^ +-----------+||revocation ||
|| | | |Complete |||references ||
|| | | |certificate||+-----------+|
|| | | | and || ^ |
|| 1 | 2 | |revocation || | |
|| | | |references || | |
|| | | +-----------+| | |
|+------------------------ | --------- | --- ^ --------+ | |
| | | 3 | / |
| | | / ---------- |
| | / / / 6 |
| | / / / |
| | / / / |
+------------------------- | ----- | -- | -- / ----------------------+
| | | |
v | | |
+--------------------+ +-----------+
| Validation Process |----->| - Valid |
+--------------------+ 4 | - Invalid |
| ^ | ^ +-----------+
v | v |
+---------+ +--------+
|Signature| |Trusted |
| Policy | |Service |
| Issuer | |Provider|
+---------+ +--------+
Figure B.9: Illustration of CAdES with eXtended validation data
CAdES-X Type 2
Before the algorithms used in any of the electronic signatures become
or are likely to be compromised or rendered vulnerable in the future,
it may be necessary to time-stamp the entire electronic signature,
including all the values of the validation and user data as an ES
with Archive validation data (CAdES-A) (7).
A CAdES-A is illustrated in Figure B.10.
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+----------------------------- CAdES-A ---------------------------+
| |
| +-- CAdES-X Long Type 1 or 2 ----------+ |
| | | +------------+ |
| | | | | |
| | | | Archive | |
| | | | Time-stamp | |
| | | | | |
| | | +------------+ |
| +---------------------------------------+ ^ |
| +----------+ ^ ^ ^ ^ | |
| | | | | | | / |
| | Signers' | | | | | / |
| | Document |\ | | | | / |
| | | \ 1 2 | 3 | 5 | 6 | 7 / |
| +----------+ \ | | | | / |
| \ | | | | / |
+----------------- \ --- | - | - | - | ------ / ------------------+
\ | | | | |
| | | | | |
| | | | | |
v v | | | |
+-----------------------------+ +-----------+
| Validation Process |----->| - Valid |
+-----------------------------+ 4 | - Invalid |
| ^ | ^ +-----------+
v | v |
+---------+ +--------+
|Signature| |Trusted |
| Policy | |Service |
| Issuer | |Provider|
+---------+ +--------+
Figure B.10: Illustration of CAdES-A
B.5. Additional Optional Features
The present document also defines additional optional features to:
- indicate a commitment type being made by the signer;
- indicate the claimed time when the signature was done;
- indicate the claimed location of the signer;
- indicate the claimed or certified role under which a signature
was created;
Pinkas, et al. Informational [Page 102]RFC 5126 CMS Advanced Electronic Signatures February 2008
- support counter signatures;
- support multiple signatures.
Annex C (Informative): General Description
This annex explains some of the concepts and provides the rationale
for normative parts of the present document.
The specification below includes a description of why and when each
component of an electronic signature is useful, with a brief
description of the vulnerabilities and threats and the manner by
which they are countered.
C.1. The Signature Policy
The signature policy is a set of rules for the creation and
validation of an electronic signature, under which the signature can
be determined to be valid. A given legal/contractual context may
recognize a particular signature policy as meeting its requirements.
A signature policy may be issued, for example, by a party relying on
the electronic signatures and selected by the signer for use with
that relying party. Alternatively, a signature policy may be
established through an electronic trading association for use amongst
its members. Both the signer and verifier use the same signature
policy.
The signature policy may be explicitly identified or may be implied
by the semantics of the data being signed and other external data,
like a contract being referenced, which itself refers to a signature
policy. An explicit signature policy has a globally unique
reference, which is bound to an electronic signature by the signer as
part of the signature calculation.
The signature policy needs to be available in human readable form so
that it can be assessed to meet the requirements of the legal and
contractual context in which it is being applied. To facilitate the
automatic processing of an electronic signature, the parts of the
signature policy, which specify the electronic rules for the creation
and validation of the electronic signature, also need to be
comprehensively defined and in a computer-processable form.
The signature policy thus includes the following:
- rules that apply to technical validation of a particular
signature;
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- rules that may be implied through adoption of Certificate
Policies that apply to the electronic signature (e.g., rules for
ensuring the secrecy of the private signing key);
- rules that relate to the environment used by the signer, e.g.,
the use of an agreed CAD (Card Accepting Device) used in
conjunction with a smart card.
For example, the major rules required for technical validation can
include:
- recognized root keys or "top-level certification authorities";
- acceptable certificate policies (if any);
- necessary certificate extensions and values (if any);
- the need for the revocation status for each component of the
certification tree;
- acceptable TSAs (if time-stamp tokens are being used);
- acceptable organizations for keeping the audit trails with
time-marks (if time-marking is being used);
- acceptable AAs (if any are being used),and;
- rules defining the components of the electronic signature that
shall be provided by the signer with data required by the
verifier when required to provide long-term proof.
C.2. Signed Information
The information being signed may be defined as a MIME-encapsulated
message that can be used to signal the format of the content in order
to select the right display or application. It can be composed of
formatted data, free text, or fields from an electronic form
(e-form). For example, the Adobe(tm) format "pdf" or the eXtensible
Mark up Language (XML) may be used. Annex D defines how the content
may be structured to indicate the type of signed data using MIME.
C.3. Components of an Electronic Signature
C.3.1. Reference to the Signature Policy
When two independent parties want to evaluate an electronic
signature, it is fundamental that they get the same result. This
requirement can be met using comprehensive signature policies that
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ensure consistency of signature validation. Signature policies can
be identified implicitly by the data being signed, or they can be
explicitly identified using the CAdES-EPES form of electronic
signature; the CAdES-EPES mandates a consistent signature policy must
be used by both the signer and verifier.
By signing over the Signature Policy Identifier in the CAdES-EPES,
the signer explicitly indicates that he or she has applied the
signature policy in creating the signature.
In order to unambiguously identify the details of an explicit
signature policy that is to be used to verify a CAdES-EPES, the
signature, an identifier, and hash of the "Signature policy" shall be
part of the signed data. Additional information about the explicit
policy (e.g., web reference to the document) may be carried as
"qualifiers" to the Signature Policy Identifier.
In order to unambiguously identify the authority responsible for
defining an explicit signature policy, the "Signature policy" can be
signed.
C.3.2. Commitment Type Indication
The commitment type can be indicated in the electronic signature
either:
- explicitly using a "commitment type indication" in the
electronic signature;
- implicitly or explicitly from the semantics of the signed data.
If the indicated commitment type is explicit using a "commitment type
indication" in the electronic signature, acceptance of a verified
signature implies acceptance of the semantics of that commitment
type. The semantics of explicit commitment type indications may be
subject to signer and verifier agreement, specified as part of the
signature policy or registered for generic use across multiple
policies.
If a CAdES-EPES electronic signature format is used and the
electronic signature includes a commitment type indication other than
one of those recognized under the signature policy, the signature
shall be treated as invalid.
How commitment is indicated using the semantics of the data being
signed is outside the scope of the present document.
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NOTE: Examples of commitment indicated through the semantics of
the data being signed are:
- an explicit commitment made by the signer indicated by the type
of data being signed over. Thus, the data structure being
signed can have an explicit commitment within the context of the
application (e.g., EDIFACT purchase order);
- an implicit commitment that is a commitment made by the signer
because the data being signed over has specific semantics
(meaning), which is only interpretable by humans, (i.e., free
text).
C.3.3. Certificate Identifier from the Signer
In many real-life environments, users will be able to get from
different CAs or even from the same CA, different certificates
containing the same public key for different names. The prime
advantage is that a user can use the same private key for different
purposes. Multiple use of the private key is an advantage when a
smart card is used to protect the private key, since the storage of a
smart card is always limited. When several CAs are involved, each
different certificate may contain a different identity, e.g., as a
citizen of a nation or as an employee from a company. Thus, when a
private key is used for various purposes, the certificate is needed
to clarify the context in which the private key was used when
generating the signature. Where there is the possibility that
multiple private keys are used, it is necessary for the signer to
indicate to the verifier the precise certificate to be used.
Many current schemes simply add the certificate after the signed data
and thus are vulnerable to substitution attacks. If the certificate
from the signer was simply appended to the signature and thus not
protected by the signature, anyone could substitute one certificate
for another, and the message would appear to be signed by someone
else. In order to counter this kind of attack, the identifier of the
signer has to be protected by the digital signature from the signer.
In order to unambiguously identify the certificate to be used for the
verification of the signature, an identifier of the certificate from
the signer shall be part of the signed data.
C.3.4. Role Attributes
While the name of the signer is important, the position of the signer
within a company or an organization is of paramount importance as
well. Some information (i.e., a contract) may only be valid if
signed by a user in a particular role, e.g., a Sales Director. In
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many cases, who the sales Director really is, is not that important,
but being sure that the signer is empowered by his company to be the
Sales Director is fundamental.
The present document defines two different ways for providing this
feature:
- by placing a claimed role name in the CMS signed attributes
field;
- by placing an attribute certificate containing a certified role
name in the CMS signed attributes field.
NOTE: Another possible approach would have been to use additional
attributes containing the roles name(s) in the signer's identity
certificate. However, it was decided not to follow this approach
as it significantly complicates the management of certificates.
For example, by using separate certificates for the signer's
identity and roles means new identity keys need not be issued if a
user's role changes.
C.3.4.1. Claimed Role
The signer may be trusted to state his own role without any
certificate to corroborate this claim; in which case, the claimed
role can be added to the signature as a signed attribute.
C.3.4.2. Certified Role
Unlike public key certificates that bind an identifier to a public
key, Attribute Certificates bind the identifier of a certificate to
some attributes, like a role. An Attribute Certificate is NOT issued
by a CA but by an Attribute Authority (AA). The Attribute Authority,
in most cases, might be under the control of an organization or a
company that is best placed to know which attributes are relevant for
which individual. The Attribute Authority may use or point to public
key certificates issued by any CA, provided that the appropriate
trust may be placed in that CA. Attribute Certificates may have
various periods of validity. That period may be quite short, e.g.,
one day. While this requires that a new Attribute Certificate be
obtained every day, valid for that day, this can be advantageous
since revocation of such certificates may not be needed. When
signing, the signer will have to specify which Attribute Certificate
it selects. In order to do so, the Attribute Certificate will have
to be included in the signed data in order to be protected by the
digital signature from the signer.
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In order to unambiguously identify the attribute certificate(s) to be
used for the verification of the signature, an identifier of the
attribute certificate(s) from the signer shall be part of the signed
data.
C.3.5. Signer Location
In some transactions, the purported location of the signer at the
time he or she applies his signature may need to be indicated. For
this reason, an optional location indicator shall be able to be
included.
In order to provide indication of the location of the signer at the
time he or she applied his signature, a location attribute may be
included in the signature.
C.3.6. Signing Time
The present document provides the capability to include a claimed
signing time as an attribute of an electronic signature.
Using this attribute, a signer may sign over a time that is the
claimed signing time. When an ES with Time is created (CAdES-T),
then either a trusted time-stamp is obtained and added to the ES or a
trusted time-mark exists in an audit trail. When a verifier accepts
a signature, the two times shall be within acceptable limits.
A further optional attribute is defined in the present document to
time-stamp the content and to provide proof of the existence of the
content, at the time indicated by the time-stamp token.
Using this optional attribute, a trusted secure time may be obtained
before the document is signed and included under the digital
signature. This solution requires an online connection to a trusted
time-stamping service before generating the signature and may not
represent the precise signing time, since it can be obtained in
advance. However, this optional attribute may be used by the signer
to prove that the signed object existed before the date included in
the time-stamp (see Section 5.11.4).
C.3.7. Content Format
When presenting signed data to a human user, it may be important that
there is no ambiguity as to the presentation of the signed
information to the relying party. In order for the appropriate
representation (text, sound, or video) to be selected by the relying
party when data (as opposed to data that has been further signed or
encrypted) is encapsulated in the SignedData (indicated by the
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RFC 5126 CMS Advanced Electronic Signatures February 2008
eContentType within EncapsulatedContentInfo being set to id-data),
further typing information should be used to identify the type of
document being signed. This is generally achieved using the MIME
content typing and encoding mechanism defined in RFC 2045 [6]).
Further information on the use of MIME is given in Annex F.
C.3.8. content-hints
The contents-hints attribute provides information on the innermost
signed content of a multi-layer message where one content is
encapsulated in another. This may be useful if the signed data is
itself encrypted.
C.3.9. Content Cross-Referencing
When presenting a signed data is in relation to another signed data,
it may be important to identify the signed data to which it relates.
The content-reference and content-identifier attributes, as defined
in ESS (RFC 2634 [5]), provide the ability to link a request and
reply messages in an exchange between two parties.
C.4. Components of Validation Data
C.4.1. Revocation Status Information
A verifier will have to ascertain that the certificate of the signer
was valid at the time of the signature. This can be done by either:
- using Certificate Revocation Lists (CRLs);
- using responses from an online certificate status server (for
example, obtained through the OCSP protocol).
NOTE 1: The time of the signature may not be known, so
time-stamping or time-marking may be used to provide the time
indication of when it was known that the signature existed.
NOTE 2: When validating an electronic signature and checking
revocation status information, if a "grace period" is required, it
needs to be suitably long enough to allow the involved authority
to process a "last-minute" revocation request and for the request
to propagate through the revocation system. This grace period is
to be added to the time included with the time-stamp token or the
time-mark, and thus the revocation status information should be
captured after the end of the grace period.
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C.4.1.1. CRL Information
When using CRLs to get revocation information, a verifier will have
to make sure that he or she gets, at the time of the first
verification, the appropriate certificate revocation information from
the signer's CA. This should be done as soon as possible to minimize
the time delay between the generation and verification of the
signature. However, a "grace period" is required to allow CAs time
to process revocation requests.
For example, a revocation request may arrive at a CA just before
issuing the next CRL, and there may not enough time to include the
revised revocation status information. This involves checking that
the signer certificate serial number is not included in the CRL.
Either the signer, the initial verifier, or a subsequent verifier may
obtain this CRL. If obtained by the signer, then it shall be
conveyed to the verifier. It may be convenient to archive the CRL
for ease of subsequent verification or arbitration. Alternatively,
provided the CRL is archived elsewhere, which is accessible for the
purpose of arbitration, then the serial number of the CRL used may be
archived together with the verified electronic signature as a CAdES-C
form.
Even if the certificate serial number appears in the CRL with the
status "suspended" (i.e., on hold), the signature is not to be deemed
as valid since a suspended certificate is not supposed to be used
even by its rightful owner.
C.4.1.2. OCSP Information
When using OCSP to get revocation information, a verifier will have
to make sure that he or she gets, at the time of the first
verification, an OCSP response that contains the status "valid".
This should be done as soon as possible after the generation of the
signature, still providing a "grace period" suitable enough to allow
the involved authority to process a "last-minute" revocation request.
The signer, the verifier, or any other third party may fetch this
OCSP response. Since OCSP responses are transient and thus are not
archived by any TSP, including CA, it is the responsibility of every
verifier to make sure that it is stored in a safe place. The
simplest way is to store them associated with the electronic
signature. An alternative would be to store them so that they can
then be easily retrieved and incorporate references to them in the
electronic signature itself as a CAdES-C form.
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In the same way as for the case of the CRL, it may happen that the
certificate is declared as invalid but with the secondary status
"suspended". In such a case, the same comment as for the CRL
applies.
C.4.2. Certification Path
A verifier may have to ascertain that the certification path was
valid, at the time of the signature, up to a trust point, according
to the:
- naming constraints;
- certificate policy constraints;
- signature policy, when applicable.
Since the time of the signature cannot be known with certainty, an
upper limit of it should be used as indicated by either the
time-stamp or time-mark.
In this case, it will be necessary to capture all the certificates
from the certification path, starting with those from the signer and
ending up with those of the self-signed certificate from one trusted
root; when applicable, this may be specified as part of the Signature
Policy. In addition, it will be necessary to capture the Certificate
Authority Revocation Lists (CARLs) to prove that none of the CAs from
the chain were revoked at the time of the signature. Again, all this
material may be incorporated in the electronic signature (ES X
forms). An alternative would be to store this information so that it
can be easily retrieved and incorporate references to it in the
electronic signature itself as a CAdES-C form.
C.4.3. Time-Stamping for Long Life of Signatures
An important property for long-standing signatures is that a
signature, having been found once to be valid, shall continue to be
so months or years later.
A signer, verifier, or both may be required to provide, on request,
proof that a digital signature was created or verified during the
validity period of all the certificates that make up the certificate
path. In this case, the signer, verifier, or both will also be
required to provide proof that the signer's certificate and all the
CA certificates used to form a valid certification path were not
revoked when the signature was created or verified.
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It would be quite unacceptable to consider a signature as invalid
even if the keys or certificates were later compromised. Thus, there
is a need to be able to demonstrate that the signature keys were
valid at the time that the signature was created to provide long-term
evidence of the validity of a signature.
It could be the case that a certificate was valid at the time of the
signature but revoked some time later. In this event, evidence shall
be provided that the document was signed before the signing key was
revoked. Time-stamping by a Time-Stamping Authority (TSA) can
provide such evidence. A time-stamp is obtained by sending the hash
value of the given data to the TSA. The returned "time-stamp" is a
signed document that contains the hash value, the identity of the
TSA, and the time of stamping. This proves that the given data
existed before the time of stamping. Time-stamping a digital
signature (by sending a hash of the signature to the TSA) before the
revocation of the signer's private key provides evidence that the
signature had been created before the certificate was revoked.
If a recipient wants to hold a valid electronic signature, he will
have to ensure that he has obtained a valid time-stamp for it before
that key (and any key involved in the validation) is revoked. The
sooner the time-stamp is obtained after the signing time, the better.
Any time-stamp or time-mark that is taken after the expiration date
of any certificate in the certification path has no value in proving
the validity of a signature.
It is important to note that signatures may be generated "off-line"
and time-stamped at a later time by anyone, for example, by the
signer or any recipient interested in the value of the signature.
The time-stamp can thus be provided by the signer, together with the
signed document, or obtained by the recipient following receipt of
the signed document.
The time-stamp is NOT a component of the Basic Electronic Signature,
but it is the essential component of the ES with Time.
It is required, in the present document, that if a signer's digital
signature value is to be time-stamped, the time-stamp token is issued
by a trusted source, known as a Time-Stamping Authority.
The present document requires that the signer's digital signature
value be time-stamped by a trusted source before the electronic
signature can become an ES with Complete validation data. Acceptable
TSAs may be specified in a Signature Validation Policy.
This technique is referred to as CAdES-C in the present document.
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Should both the signer and verifier be required to time-stamp the
signature value to meet the requirements of the signature policy, the
signature policy may specify a permitted time delay between the two
time-stamps.
C.4.4. Time-Stamping for Long Life of Signature before CA Key
Compromises
Time-stamped, extended electronic signatures are needed when there is
a requirement to safeguard against the possibility of a CA key in the
certificate chain ever being compromised. A verifier may be required
to provide, on request, proof that the certification path and the
revocation information used at the time of the signature were valid,
even in the case where one of the issuing keys or OCSP responder keys
is later compromised.
The present document defines two ways of using time-stamps to protect
against this compromise:
- time-stamp the ES with Complete validation data, when an OCSP
response is used to get the status of the certificate from the
signer (CAdES-X Type 1). This format is suitable to be used
with an OCSP response, and it offers the additional advantage of
providing an integrity protection over the whole data;
- time-stamp only the certification path and revocation
information references when a CRL is used to get the status of
the certificate from the signer (CAdES-X Type2). This format is
suitable to be used with CRLs, since the time-stamped
information may be used for more than one signature (when
signers have their certificates issued by the same CA and when
signatures can be checked using the same CRLs).
NOTE: The signer, verifier, or both may obtain the time-stamp.
C.4.4.1. Time-Stamping the ES with Complete Validation Data (CAdES-X
Type 1)
When an OCSP response is used, it is necessary to time-stamp in
particular that response in the case the key from the responder would
be compromised. Since the information contained in the OCSP response
is user specific and time specific, an individual time-stamp is
needed for every signature received. Instead of placing the
time-stamp only over the certification path references and revocation
information references, which include the OCSP response, the
time-stamp is placed on the CAdES-C. Since the certification path
and revocation information references are included in the ES with
Complete validation data, they are also protected. For the same
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cryptographic price, this provides an integrity mechanism over the ES
with Complete validation data. Any modification can be immediately
detected. It should be noticed that other means of
protecting/detecting the integrity of the ES with Complete validation
data exist and could be used. Although the technique requires a
time-stamp for every signature, it is well suited for individual
users wishing to have an integrity-protected copy of all the
validated signatures they have received.
By time-stamping the complete electronic signature, including the
digital signature as well as the references to the certificates and
revocation status information used to support validation of that
signature, the time-stamp ensures that there is no ambiguity in the
means of validating that signature.
This technique is referred to as CAdES-X Type 1 in the present
document.
NOTE: Trust is achieved in the references by including a hash of
the data being referenced.
If it is desired for any reason to keep a copy of the additional data
being referenced, the additional data may be attached to the
electronic signature, in which case the electronic signature becomes
a CAdES-X Long Type 1, as defined by the present document.
A CAdES-X Long Type 1 is simply the concatenation of a CAdES-X Type
1, with a copy of the additional data being referenced.
C.4.4.2. Time-Stamping Certificates and Revocation Information
References (CAdES-X Type 2)
Time-stamping each ES with Complete validation data, as defined
above, may not be efficient, particularly when the same set of CA
certificates and CRL information is used to validate many signatures.
Time-stamping CA certificates will stop any attacker from issuing
bogus CA certificates that could be claimed to exist before the CA
key was compromised. Any bogus time-stamped CA certificates will
show that the certificate was created after the legitimate CA key was
compromised. In the same way, time-stamping CA CRLs will stop any
attacker from issuing bogus CA CRLs that could be claimed to exist
before the CA key was compromised.
Time-stamping of commonly used certificates and CRLs can be done
centrally, e.g., inside a company or by a service provider. This
method reduces the amount of data the verifier has to time-stamp; for
example, it could be reduced to just one time-stamp per day (i.e., in
Pinkas, et al. Informational [Page 114]RFC 5126 CMS Advanced Electronic Signatures February 2008
the case where all the signers use the same CA, and the CRL applies
for the whole day). The information that needs to be time-stamped is
not the actual certificates and CRLs, but the unambiguous references
to those certificates and CRLs.
This technique is referred to as CAdES-X Type 2 in the present
document and requires the following:
- all the CA certificates references and revocation information
references (i.e., CRLs) used in validating the CAdES-C are
covered by one or more time-stamps.
Thus, a CAdES-C with a time-stamp signature value at time T1 can be
proved valid if all the CA and CRL references are time-stamped at
time T1+.
C.4.5. Time-Stamping for Archive of Signature
Advances in computing increase the probability of being able to break
algorithms and compromise keys. There is therefore a requirement to
be able to protect electronic signatures against this possibility.
Over a period of time, weaknesses may occur in the cryptographic
algorithms used to create an electronic signature (e.g., due to the
time available for cryptoanalysis, or improvements in
cryptoanalytical techniques). Before such weaknesses become likely,
a verifier should take extra measures to maintain the validity of the
electronic signature. Several techniques could be used to achieve
this goal, depending on the nature of the weakened cryptography. In
order to simplify matters, a single technique called Archive
validation data, covering all the cases, is being used in the present
document.
Archive validation data consists of the validation data and the
complete certificate and revocation data, time-stamped together with
the electronic signature. The Archive validation data is necessary
if the hash function and the crypto algorithms that were used to
create the signature are no longer secure. Also, if it cannot be
assumed that the hash function used by the Time-Stamping Authority is
secure, then nested time-stamps of the Archived Electronic Signature
are required.
The potential for a Trusted Service Provider (TSP) key compromise
should be significantly lower than user keys because TSP(s) are
expected to use stronger cryptography and better key protection. It
can be expected that new algorithms (or old ones with greater key
lengths) will be used. In such a case, a sequence of time-stamps
will protect against forgery. Each time-stamp needs to be affixed
Pinkas, et al. Informational [Page 115]RFC 5126 CMS Advanced Electronic Signatures February 2008
before either the compromise of the signing key or the cracking of
the algorithms used by the TSA. TSAs (Time-Stamping Authorities)
should have long keys (e.g., which at the time of drafting the
present document was at least 2048 bits for the signing RSA
algorithm) and/or a "good" or different algorithm.
Nested time-stamps will also protect the verifier against key
compromise or cracking the algorithm on the old electronic
signatures.
The process will need to be performed and iterated before the
cryptographic algorithms used for generating the previous time-stamp
are no longer secure. Archive validation data may thus bear multiple
embedded time-stamps.
This technique is referred to as CAdES-A in the present document.
C.4.6. Reference to Additional Data
Using CAdES-X Type 1 or CAdES-X Type 2 extended validation data,
verifiers still need to keep track of all the components that were
used to validate the signature, in order to be able to retrieve them
again later on. These components may be archived by an external
source, like a Trusted Service Provider; in which case, referenced
information that is provided as part of the ES with Complete
validation data (CAdES-C) is adequate. The actual certificates and
CRL information reference in the CAdES-C can be gathered when needed
for arbitration.
If references to additional data are not adequate, then the actual
values of all the certificates and revocation information required
may be part of the electronic signature. This technique is referred
to as CAdES-X Long Type 1 or CAdES-X Long Type 2 in the present
document.
C.4.7. Time-Stamping for Mutual Recognition
In some business scenarios, both the signer and the verifier need to
time-stamp their own copy of the signature value. Ideally, the two
time-stamps should be as close as possible to each other.
EXAMPLE: A contract is signed by two parties, A and B,
representing their respective organizations; to time-stamp the
signer and verifier data, two approaches are possible:
- under the terms of the contract, a predefined common
"trusted" TSA may be used;
Pinkas, et al. Informational [Page 116]RFC 5126 CMS Advanced Electronic Signatures February 2008
- if both organizations run their own time-stamping services, A
and B can have the transaction time-stamped by these two
time-stamping services.
In the latter case, the electronic signature will only be considered
valid if both time-stamps were obtained in due time (i.e., there
should not be a long delay between obtaining the two time-stamps).
Thus, neither A nor B can repudiate the signing time indicated by
their own time-stamping service. Therefore, A and B do not need to
agree on a common "trusted" TSA to get a valid transaction.
It is important to note that signatures may be generated "off-line"
and time-stamped at a later time by anyone, e.g., by the signer or
any recipient interested in validating the signature. The time-stamp
over the signature from the signer can thus be provided by the
signer, together with the signed document, and/or be obtained by the
verifier following receipt of the signed document.
The business scenarios may thus dictate that one or more of the
long-term signature time-stamping methods described above be used.
This may be part of a mutually agreed Signature Validation Policy
that is part of an agreed signature policy under which digital
signatures may be used to support the business relationship between
the two parties.
C.4.8. TSA Key Compromise
TSA servers should be built in such a way that once the private
signature key is installed, there is minimal likelihood of compromise
over as long as a possible period. Thus, the validity period for the
TSA's keys should be as long as possible.
Both the CAdES-T and the CAdES-C contain at least one time-stamp over
the signer's signature. In order to protect against the compromise
of the private signature key used to produce that time-stamp, the
Archive validation data can be used when a different Time-Stamping
Authority key is involved to produce the additional time-stamp. If
it is believed that the TSA key used in providing an earlier
time-stamp may ever be compromised (e.g., outside its validity
period), then the CAdES-A should be used. For extremely long
periods, this may be applied repeatedly using new TSA keys.
This technique is referred to as a nested CAdES-A in the present
document.
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C.5. Multiple Signatures
Some electronic signatures may only be valid if they bear more than
one signature. This is generally the case when a contract is signed
between two parties. The ordering of the signatures may or may not
be important, i.e., one may or may not need to be applied before the
other.
Several forms of multiple and counter signatures need to be
supported, which fall into two basic categories:
- independent signatures;
- embedded signatures.
Independent signatures are parallel signatures where the ordering of
the signatures is not important. The capability to have more than
one independent signature over the same data shall be provided.
Embedded signatures are applied one after the other and are used
where the order in which the signatures are applied is important.
The capability to sign over signed data shall be provided.
These forms are described in Section 5.13. All other multiple
signature schemes, e.g., a signed document with a countersignature,
double countersignatures, or multiple signatures can be reduced to
one or more occurrences of the above two cases.
Annex D (Informative): Data Protocols to Interoperate with TSPs
D.1. Operational Protocols
The following protocols can be used by signers and verifiers to
interoperate with Trusted Service Providers during the electronic
signature creation and validation.
D.1.1. Certificate Retrieval
User certificates, CA certificates, and cross-certificates can be
retrieved from a repository using the Lightweight Directory Access
Protocol as defined in RFC 3494 [RFC3494], with the schema defined in
RFC 4523 [RFC4523].
D.1.2. CRL Retrieval
Certificate revocation lists, including authority revocation lists
and partial CRL variants, can be retrieved from a repository using
the Lightweight Directory Access Protocol, as defined in RFC 3494
[RFC3494], with the schema defined in RFC 4523 [RFC4523].
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D.1.3. Online Certificate Status
As an alternative to the use of certificate revocation lists, the
status of a certificate can be checked using the Online Certificate
Status Protocol (OCSP), as defined in RFC 2560 [3].
D.1.4. Time-Stamping
The time-stamping service can be accessed using the Time-Stamping
Protocol defined in RFC 3161 [7].
D.2. Management Protocols
Signers and verifiers can use the following management protocols to
manage the use of certificates.
D.2.1. Request for Certificate Revocation
Request for a certificate to be revoked can be made using the
revocation request and response messages defined in RFC 4210
[RFC4210].
Annex E (Informative): Security Considerations
E.1. Protection of Private Key
The security of the electronic signature mechanism defined in the
present document depends on the privacy of the signer's private key.
Implementations should take steps to ensure that private keys cannot
be compromised.
E.2. Choice of Algorithms
Implementers should be aware that cryptographic algorithms become
weaker with time. As new cryptoanalysis techniques are developed and
computing performance improves, the work factor to break a particular
cryptographic algorithm will reduce. Therefore, cryptographic
algorithm implementations should be modular, allowing new algorithms
to be readily inserted. That is, implementers should be prepared for
the set of mandatory-to-implement algorithms to change over time.
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Annex F (Informative): Example Structured Contents and MIME
F.1. Use of MIME to Encode Data
The signed content may be structured using MIME (Multipurpose
Internet Mail Extensions -- RFC 2045 [6]). Whilst the MIME structure
was initially developed for Internet email, it has a number of
features that make it useful to provide a common structure for
encoding a range of electronic documents and other multi-media data
(e.g., photographs, video). These features include:
- providing a means of signalling the type of "object" being
carried (e.g., text, image, ZIP file, application data);
- providing a means of associating a file name with an object;
- associating several independent objects (e.g., a document and
image) to form a multi-part object;
- handling data encoded in text or binary and, if necessary,
re-encoding the binary as text.
When encoding a single object, MIME consists of:
- header information, followed by;
- encoded content.
This structure can be extended to support multi-part content.
F.1.1. Header Information
A MIME header includes:
MIME Version information: e.g., MIME-Version: 1.0
Content type information, which includes information describing the
content sufficient for it to be presented to a user or application
process, as required. This includes information on the "media type"
(e.g., text, image, audio) or whether the data is for passing to a
particular type of application. In the case of text, the content
type includes information on the character set used, e.g.,
Content-Type: text/plain; charset="us-ascii".
Content-encoding information, which defines how the content is
encoded (see below about encoding supported by MIME).
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Other information about the content, such as a description or an
associated file name.
An example MIME header for text object is:
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable
An example MIME header for a binary file containing a pdf document
is:
Content-Type: application/pdf
Content-Transfer-Encoding: base64
Content-Description: JCFV201.pdf
Content-Disposition: filename="JCFV201.pdf"
F.1.2. Content Encoding
MIME supports a range of mechanisms for encoding both text and binary
data.
Text data can be carried transparently as lines of text data encoded
in 7- or 8-bit ASCII characters. MIME also includes a
"quoted-printable" encoding that converts characters other than the
basic ASCII into an ASCII sequence.
Binary can either be carried:
- transparently as 8-bit octets; or
- converted to a basic set of characters using a system called
Base64.
NOTE: As there are some mail relays that can only handle 7-bit
ASCII, Base64 encoding is usually used on the Internet.
F.1.3. Multi-Part Content
Several objects (e.g., text and a file attachment) can be associated
together using a special "multi-part" content type. This is
indicated by the content type "multipart" with an indication of the
string to be used indicating a separation between each part.
In addition to a header for the overall multipart content, each part
includes its own header information indicating the inner content type
and encoding.
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An example of a multipart content is:
Mime-Version: 1.0
Content-Type: multipart/mixed; boundary="----
=_NextPart_000_01BC4599.98004A80"
Content-Transfer-Encoding: 7bit
------=_NextPart_000_01BC4599.98004A80
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Per your request, I've attached our proposal for the Java Card Version
2.0 API and the Java Card FAQ.
------=_NextPart_000_01BC4599.98004A80
Content-Type: application/pdf; name="JCFV201.pdf"
Content-Transfer-Encoding: base64
Content-Description: JCFV201.pdf
Content-Disposition: attachment; filename="JCFV201.pdf"
0M8R4KGxGuEAAAAAAAAAAAAAAAAAAAAAPgADAP7/CQAGAAAAAAAAAAAAAAACAAAAAgAAAAA
AAAAAEAAAtAAAAAEAAAD+////AAAAAAMAAAAGAAAA//////////////////////////////
//////////AANhAAQAYg==
------=_NextPart_000_01BC4599.98004A80--
Multipart content can be nested. So a set of associated objects
(e.g., HTML text and images) can be handled as a single attachment to
another object (e.g., text).
The Content-Type from each part of the S/MIME message indicates the
type of content.
F.2. S/MIME
The specific use of MIME to carry CMS (extended as defined in the
present document) secured data is called S/MIME (see [RFC3851]).
S/MIME carries electronic signatures as either:
- an "application/pkcs7-mime" object with the CMS carried as a
binary attachment (PKCS7 is the name of the early version of
CMS).
The signed data may be included in the SignedData, which itself
may be included in a single S/MIME object. See [RFC3851],
Section 3.4.2: "Signing Using application/pkcs7-mime with
SignedData" and Figure F.1 hereafter.
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or
- a "multipart/signed" object with the signed data and the
signature encoded as separate MIME objects.
The signed data is not included in the SignedData, and the CMS
structure only includes the signature. See [RFC3851], Section
3.4.3: "Signing Using the multipart/signed Format" and Figure
F.2 hereafter.
+-------------++----------++-------------++------------+
| || || || |
| S/MIME || CAdES || MIME || pdf file |
| || || || |
|Content-Type=||SignedData||Content-Type=||Dear MrSmith|
|application/ || eContent ||application/ ||Received |
|pkcs7-mime || ||pdf || 100 tins |
| || || || |
|smime-type= || /| || /| || Mr.Jones |
|signed-data || / -----+ / ------+ |
| || \ -----+ \ ------+ |
| || \| || \| |+------------+
| || |+-------------+
| |+----------+
+-------------+
Figure F.1: Signing Using application/pkcs7-mime
F.2.1. Using application/pkcs7-mime
This approach is similar to handling signed data as any other binary
file attachment.
An example of signed data encoded using this approach is:
Content-Type: application/pkcs7-mime; smime-type=signed-data;
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename=smime.p7m
567GhIGfHfYT6ghyHhHUujpfyF4f8HHGTrfvhJhjH776tbB9HG4VQbnj7
77n8HHGT9HG4VQpfyF467GhIGfHfYT6rfvbnj756tbBghyHhHUujhJhjH
HUujhJh4VQpfyF467GhIGfHfYGTrfvbnjT6jH7756tbB9H7n8HHGghyHh
6YT64V0GhIGfHfQbnj75
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F.2.2. Using application/pkcs7-signature
CMS also supports an alternative structure where the signature and
data being protected are separate MIME objects carried within a
single message. In this case, the signed data is not included in the
SignedData, and the CMS structure only includes the signature. See
[RFC3851], Section 3.4.3: "Signing Using the multipart/signed Format"
and Figure F.2 hereafter.
An example of signed data encoded using this approach is:
Content-Type: multipart/signed;
protocol="application/pkcs7-signature";
micalg=sha1; boundary=boundary42
--boundary42
Content-Type: text/plain
This is a clear-signed message.
--boundary42
Content-Type: application/pkcs7-signature; name=smime.p7s
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename=smime.p7s
ghyHhHUujhJhjH77n8HHGTrfvbnj756tbB9HG4VQpfyF467GhIGfHfYT6
4VQpfyF467GhIGfHfYT6jH77n8HHGghyHhHUujhJh756tbB9HGTrfvbnj
n8HHGTrfvhJhjH776tbB9HG4VQbnj7567GhIGfHfYT6ghyHhHUujpfyF4
7GhIGfHfYT64VQbnj756
--boundary42--
With this second approach, the signed data passes through the CMS
process and is carried as part of a multiple-parts signed MIME
structure, as illustrated in Figure F.2. The CMS structure just
holds the electronic signature.
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+---------------++----------++-------------++------------+
| || || || |
| MIME || CAdES || MIME || pdf file |
| || || || |
|Content-Type= ||SignedData||Content-Type=||Dear MrSmith|
|multipart/ || ||application/ ||Received |
|signed || ||pdf || 100 tins |
| /| || || || |
| / -------------------+ /| || Mr.Jones |
| \ -------------------+ / -----+ |
| \| || || \ -----+ |
|Content-Type= || || \| |+------------+
|application/ || |+-------------+
|pdf || |
| || |
|Content-Type= || |
|application/ || |
|pkcs7-signature|| |
| || |
| /| || |
| / -------+ |
| \ -------+ |
| \| ||----------+
| |
+---------------+
Figure F.2: Signing Using application/pkcs7-signature
This second approach (multipart/signed) has the advantage that the
signed data can be decoded by any MIME-compatible system even if it
does not recognize CMS-encoded electronic signatures.
Annex G (Informative): Relationship to the European Directive and EESSI
G.1. Introduction
This annex provides an indication of the relationship between
electronic signatures created under the present document and
requirements under the European Parliament and Council Directive on a
Community framework for electronic signatures.
NOTE: Legal advice should be sought on the specific national
legislation regarding use of electronic signatures.
The present document is one of a set of standards that has been
defined under the "European Electronic Signature Standardization
Initiative" (EESSI) for electronic signature products and solutions
compliant with the European Directive for Electronic Signatures.
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G.2. Electronic Signatures and the Directive
This directive defines electronic signatures as:
- "data in electronic form which are attached to or logically
associated with other electronic data and which serve as a
method of authentication".
The directive states that an electronic signature should not be
denied "legal effectiveness and admissibility as evidence in legal
proceedings" solely on the grounds that it is in electronic form.
The directive identifies an electronic signature as having
equivalence to a hand-written signature if it meets specific
criteria:
- it is an "advanced electronic signature" with the following
properties:
a) it is uniquely linked to the signatory;
b) it is capable of identifying the signatory;
c) it is created using means that the signatory can maintain
under his sole control; and
d) it is linked to the data to which it relates in such a
manner that any subsequent change of the data is detectable.
- it is based on a certificate that meets detailed criteria given
in Annex I of the directive and is issued by a
"certification-service-provider" that meets requirements given
in Annex II of the directive. Such a certificate is referred to
as a "qualified certificate";
- it is created by a "device", for which detailed criteria are
given in Annex III of the directive. Such a device is referred
to a "secure-signature-creation device".
This form of electronic signature is referred to as a "qualified
electronic signature" in EESSI (see below).
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G.3. ETSI Electronic Signature Formats and the Directive
An electronic signature created in accordance with the present
document is:
a) considered to be an "electronic signature" under the terms of
the Directive;
b) considered to be an "advanced electronic signature" under the
terms of the Directive;
c) considered to be a "Qualified Electronic Signature", provided
the additional requirements in Annex I, II, and III of the
Directive are met. The requirements in Annex I, II, and III of
the Directive are outside the scope of the present document,
and are subject to standardization elsewhere.
G.4. EESSI Standards and Classes of Electronic Signature
G.4.1. Structure of EESSI Standardization
EESSI looks at standards in several areas. See the ETSI and CEN web
sites for the latest list of standards and their versions:
- use of X.509 public key certificates as qualified certificates;
- security Management and Certificate Policy for CSPs Issuing
Qualified Certificates;
- security requirements for trustworthy systems used by CSPs
Issuing Qualified Certificates;
- security requirements for Secure Signature Creation Devices;
- security requirements for Signature Creation Systems;
- procedures for Electronic Signature Verification;
- electronic signature syntax and encoding formats;
- protocol to interoperate with a Time-Stamping Authority;
- Policy requirements for Time-Stamping Authorities; and
- XML electronic signature formats.
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Each of these standards addresses a range of requirements, including
the requirements of Qualified Electronic Signatures, as specified in
Article 5.1 of the Directive. However, some of them also address
general requirements of electronic signatures for business and
electronic commerce, which all fall into the category of Article 5.2
of the Directive. Such variation in the requirements may be
identified either as different levels or different options.
G.4.2. Classes of Electronic Signatures
Since some of these standards address a range of requirements, it may
be useful to identify a set of standards to address a specific
business need. Such a set of standards and their uses define a class
of electronic signature. The first class already identified is the
qualified electronic signature, fulfilling the requirements of
Article 5.1 of the Directive.
A limited number of "classes of electronic signatures" and
corresponding profiles could be defined in close cooperation with
actors on the market (business, users, suppliers). The need for such
standards is envisaged, in addition to those for qualified electronic
signatures, in areas such as:
- different classes of electronic signatures with long-term
validity;
- electronic signatures for business transactions with limited
value.
G.4.3. Electronic Signature Classes and the ETSI Electronic Signature
Format
The electronic signature format defined in the present document is
applicable to the EESSI area "electronic signature and encoding
formats".
An electronic signature produced by a signer (see Section 5 and
conformance Section 10.1) is applicable to the proposed class of
electronic signature: "qualified electronic signatures fulfilling
article 5.1".
With the addition of attributes by the verifier (see Section 6 and
conformance Section 10.2) the qualified electronic signature supports
long-term validity.
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Annex H (Informative): APIs for the Generation and Verification of
Electronic Signatures Tokens
While the present document describes the data format of an electronic
signature, the question is whether there exist APIs (Application
Programming Interfaces) able to manipulate these structures. At
least two such APIs have been defined; one set by the IETF and
another set by the OMG (Object Management Group).
H.1. Data Framing
In order to be able to use either of these APIs, it will be necessary
to frame the previously defined electronic signature data structures
using a mechanism-independent token format. Section 3.1 of RFC 2743
[RFC2743] specifies a mechanism-independent level of encapsulating
representation for the initial token of a GSS-API context
establishment sequence, incorporating an identifier of the mechanism
type to be used on that context and enabling tokens to be interpreted
unabmiguously.
In order to be processable by these APIs, all electronic signature
data formats that are defined in the present document shall be framed
following that description.
The encoding format for the token tag is derived from ASN.1 and DER,
but its concrete representation is defined directly in terms of
octets rather than at the ASN.1 level, in order to facilitate
interoperable implementation without use of general ASN.1 processing
code. The token tag consists of the following elements, in order:
1) 0x60 -- Tag for RFC 2743 SEQUENCE; indicates that constructed
form, definite length encoding follows.
2) Token-length octets, specifying length of subsequent data
(i.e., the summed lengths of elements 3 to 5 in this list, and
of the mechanism-defined token object following the tag). This
element comprises a variable number of octets:
a) If the indicated value is less than 128, it shall be
represented in a single octet with bit 8 (high order) set to
"0" and the remaining bits representing the value.
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b) If the indicated value is 128 or more, it shall be
represented in two or more octets, with bit 8 of the first
octet set to "1" and the remaining bits of the first octet
specifying the number of additional octets. The subsequent
octets carry the value, 8 bits per octet, with the most
significant digit first. The minimum number of octets shall
be used to encode the length (i.e., no octets representing
leading zeros shall be included within the length encoding).
3) 0x06 -- Tag for OBJECT IDENTIFIER.
4) Object identifier length -- length (number of octets) of the
encoded object identifier contained in element 5, encoded per
rules as described in 2a) and 2b) above.
5) object identifier octets -- variable number of octets, encoded
per ASN.1 BER rules:
- The first octet contains the sum of two values:
(1) the top-level object identifier component, multiplied by
40 (decimal); and
(2) the second-level object identifier component.
This special case is the only point within an object
identifier encoding where a single octet represents
contents of more than one component.
- Subsequent octets, if required, encode successively lower
components in the represented object identifier. A
component's encoding may span multiple octets, encoding 7
bits per octet (most significant bits first) and with bit
8 set to "1" on all but the final octet in the component's
encoding. The minimum number of octets shall be used to
encode each component (i.e., no octets representing
leading zeros shall be included within a component's
encoding).
NOTE: In many implementations, elements 3 to 5 may be stored and
referenced as a contiguous string constant.
The token tag is immediately followed by a mechanism-defined token
object. Note that no independent size specifier intervenes following
the object identifier value to indicate the size of the
mechanism-defined token object.
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Tokens conforming to the present document shall have the following
OID in order to be processable by IDUP-APIs:
id-etsi-es-IDUP-Mechanism-v1 OBJECT IDENTIFIER ::=
{ itu-t(0) identified-organization(4) etsi(0)
electronic-signature-standard (1733) part1 (1) IDUPMechanism (4)
etsiESv1(1) }
H.2. IDUP-GSS-APIs Defined by the IETF
The IETF CAT WG produced, in December 1998, an RFC (RFC 2479
[RFC2479]) under the name of IDUP-GSS-API (Independent Data Unit
Protection) able to handle the electronic signature data format
defined in the present document.
The IDUP-GSS-API includes support for non-repudiation services.
It supports evidence generation, where "evidence" is information that
either by itself, or when used in conjunction with other information,
is used to establish proof about an event or action, as well as
evidence verification.
IDUP supports various types of evidences. All the types defined in
IDUP are supported in the present document through the
commitment-type parameter.
Section 2.3.3 of IDUP describes the specific calls needed to handle
evidence ("EV" calls). The "EV" group of calls provides a simple,
high-level interface to underlying IDUP mechanisms when application
developers need to deal with only evidence: not with encryption or
integrity services.
All generations and verification are performed according to the
content of a NR policy that is referenced in the context.
Get_token_details is used to return the attributes that correspond to
a given input token to an application. Since IDUP-GSS-API tokens are
meant to be opaque to the calling application, this function allows
the application to determine information about the token without
having to violate the opaqueness intention of IDUP. Of primary
importance is the mechanism type, which the application can then use
as input to the IDUP_Establish_Env() call in order to establish the
correct environment in which to have the token processed.
Generate_token generates a non-repudiation token using the current
environment.
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Verify_evidence verifies the evidence token using the current
environment. This operation returns a major_status code that can be
used to determine whether the evidence contained in a token is
complete (i.e., can be successfully verified (perhaps years) later).
If a token's evidence is not complete, the token can be passed to
another API, form_complete_pidu, to complete it. This happens when a
status "conditionally valid" is returned. That status corresponds to
the status "validation incomplete" of the present document.
Form_complete_PIDU is used primarily when the evidence token itself
does not contain all the data required for its verification, and it
is anticipated that some of the data not stored in the token may
become unavailable during the interval between generation of the
evidence token and verification unless it is stored in the token.
The Form_Complete_PIDU operation gathers the missing information and
includes it in the token so that verification can be guaranteed to be
possible at any future time.
H.3. CORBA Security Interfaces Defined by the OMG
Non-repudiation interfaces have been defined in "CORBA Security", a
document produced by the OMG (Object Management Group). These
interfaces are described in IDL (Interface Definition Language) and
are optional.
The handling of "tokens" supporting non-repudiation is done through
the following interfaces:
- set_NR_features specifies the features to apply to future
evidence generation and verification operations;
- get_NR_features returns the features that will be applied to
future evidence generation and verification operations;
- generate_token generates a non-repudiation token using the
current non-repudiation features;
- verify_evidence verifies the evidence token using the current
non-repudiation features;
- get_tokens_details returns information about an input
non-repudiation token. The information returned depends upon
the type of token;
- form_complete_evidence is used when the evidence token itself
does not contain all the data required for its verification, and
it is anticipated that some of the data not stored in the token
may become unavailable during the interval between generation of
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the evidence token and verification unless it is stored in the
token. The form_complete_evidence operation gathers the missing
information and includes it in the token so that verification
can be guaranteed to be possible at any future time.
NOTE: The similarity between the two sets of APIs is noticeable.
Annex I (Informative): Cryptographic Algorithms
RFC 3370 [10] describes the conventions for using several
cryptographic algorithms with the Crytographic Message Syntax (CMS).
Only the hashing and signing algorithms are appropriate for use with
the present document.
Since the publication of RFC 3370 [10], MD5 has been broken. This
algorithm is no longer considered appropriate and has been deleted
from the list of algorithms.
I.1. Digest Algorithms
I.1.1. SHA-1
The SHA-1 digest algorithm is defined in FIPS Pub 180-1. The
algorithm identifier for SHA-1 is:
sha-1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3) oiw(14)
secsig(3) algorithm(2) 26 }
The AlgorithmIdentifier parameters field is optional. If present,
the parameters field shall contain an ASN.1 NULL. Implementations
should accept SHA-1 AlgorithmIdentifiers with absent parameters as
well as NULL parameters. Implementations should generate SHA-1
AlgorithmIdentifiers with NULL parameters.
I.1.2. General
The following is a selection of work that has been done in the area
of digest algorithms or, as they are often called, hash functions:
- ISO/IEC 10118-1 (1994) [ISO10118-1]: "Information technology -
Security techniques - Hash-functions - Part 1: General". ISO/IEC
10118-1 contains definitions and describes basic concepts.
- ISO/IEC 10118-2 (1994) [ISO10118-2]: "Information technology -
Security techniques - Hash-functions - Part 2: Hash-functions
using an n-bit block cipher algorithm". ISO/IEC 10118-2
specifies two ways to construct a hash-function from a block
cipher.
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- ISO/IEC 10118-3 (1997) [ISO10118-3]: "Information technology -
Security techniques - Hash-functions - Part 3: Dedicated
hash-functions". ISO/IEC 10118-3 specifies the following
dedicated hash-functions:
- SHA-1 (FIPS 180-1);
- RIPEMD-128;
- RIPEMD-160.
- ISO/IEC 10118-4 (1998) [ISO10118-4]: "Information technology -
Security techniques - Hash-functions - Part 4: Hash-functions
using modular arithmetic".
- RFC 1320 (PS 1992): "The MD4 Message-Digest Algorithm". RFC
1320 specifies the hash-function MD4. Today, MD4 is considered
outdated.
- RFC 1321 (I 1992): "The MD5 Message-Digest Algorithm". RFC 1321
(informational) specifies the hash-function MD5. Today, MD5 is
not recommended for new implementations.
- FIPS Publication 180-1 (1995): "Secure Hash Standard". FIPS
180-1 specifies the Secure Hash Algorithm (SHA), dedicated hash-
function developed for use with the DSA. The original SHA,
published in 1993, was slightly revised in 1995 and renamed
SHA-1.
- ANSI X9.30-2 (1997) [X9.30-2]: "Public Key Cryptography for the
Financial Services Industry - Part 2: The Secure Hash Algorithm
(SHA-1)". X9.30-2 specifies the ANSI-Version of SHA-1.
- ANSI X9.31-2 (1996) [X9.31-2]: "Public Key Cryptography Using
Reversible Algorithms for the Financial Services Industry - Part
2: Hash Algorithms". X9.31-2 specifies hash algorithms.
I.2. Digital Signature Algorithms
I.2.1. DSA
The DSA signature algorithm is defined in FIPS Pub 186. DSA is
always used with the SHA-1 message digest algorithm. The algorithm
identifier for DSA is:
id-dsa-with-sha1 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
x9-57 (10040) x9cm(4) 3 }
The AlgorithmIdentifier parameters field shall not be present.
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I.2.2. RSA
The RSA signature algorithm is defined in RFC 3447 [RFC3447]. RFC
3370 [10] specifies the use of the RSA signature algorithm with the
SHA-1 algorithm. The algorithm identifier for RSA with SHA-1 is:
Sha1WithRSAEncryption OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-1(1) 5 }
NOTE: RFC 3370 [10] recommends that MD5 not be used for new
implementations.
I.2.3. General
The following is a selection of work that has been done in the
area of digital signature mechanisms:
- FIPS Publication 186 (1994): "Digital Signature Standard".
NIST's Digital Signature Algorithm (DSA) is a variant of
ElGamal's Discrete Logarithm-based digital signature mechanism.
The DSA requires a 160-bit hash-function and mandates SHA-1.
- IEEE P1363 (2000) [P1363]: "Standard Specifications for Public-
Key Cryptography". IEEE P1363 contains mechanisms for digital
signatures, key establishment, and encipherment based on three
families of public key schemes:
- "Conventional" Discrete Logarithm (DL)-based techniques, i.e.,
Diffie-Hellman (DH) key agreement, Menezes-Qu-Vanstone (MQV) key
agreement, the Digital Signature Algorithm (DSA), and
Nyberg-Rueppel (NR) digital signatures;
- Elliptic Curve (EC)-based variants of the DL-mechanisms
specified above, i.e., EC-DH, EC-MQV, EC-DSA, and EC-NR. For
elliptic curves, implementation options include mod p and
characteristic 2 with polynomial or normal basis representation;
- Integer Factoring (IF)-based techniques, including RSA
encryption, RSA digital signatures, and RSA-based key transport.
- ISO/IEC 9796-2 (1997) [ISO9796-2]: "Information technology -
Security techniques - Digital signature schemes giving message
recovery - Part 2: Mechanisms using a hash-function". ISO/IEC
9796-2 specifies digital signature mechanisms with partial
message recovery that are also based on the RSA technique but
make use of a hash-function.
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- ISO/IEC 9796-4 (1998) [ISO9796-4]: "Digital signature schemes
giving message recovery - Part 4: Discrete logarithm based
mechanisms". ISO/IEC 9796-4 specifies digital signature
mechanisms with partial message recovery that are based on
Discrete Logarithm techniques. The document includes the
Nyberg-Rueppel scheme.
- ISO/IEC 14888-1 [ISO14888-1]: "Digital signatures with appendix
- Part 1: General". ISO/IEC 14888-1 contains definitions and
describes the basic concepts of digital signatures with
appendix.
- ISO/IEC 14888-2 [ISO14888-2]: "Digital signatures with appendix
- Part 2: Identity-based mechanisms". ISO/IEC 14888-2 specifies
digital signature schemes with appendix that make use of
identity-based keying material. The document includes the
zero-knowledge techniques of Fiat-Shamir and Guillou-Quisquater.
- ISO/IEC 14888-3 [ISO14888-3]: "Digital signatures with appendix
- Part 3: Certificate-based mechanisms". ISO/IEC 14888-3
specifies digital signature schemes with appendix that make use
of certificate-based keying material. The document includes
five schemes:
- DSA;
- EC-DSA, an elliptic curve-based analog of NIST's Digital
Signature Algorithm;
- Pointcheval-Vaudeney signatures;
- RSA signatures;
- ESIGN.
- ISO/IEC 15946-2 (2002) [ISO15946-2]: "Cryptographic techniques
based on elliptic curves - Part 2: Digital signatures",
specifies digital signature schemes with appendix using elliptic
curves.
- The document includes two schemes:
- EC-DSA, an elliptic curve-based analog of NIST's Digital
Signature Algorithm;
- EC-AMV, an elliptic curve-based analog of the Agnew-Muller-
Vanstone signature algorithm.
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- ANSI X9.31-1 (1997) [X9.31-1]: "Public Key Cryptography Using
Reversible Algorithms for the Financial Services Industry - Part
1: The RSA Signature Algorithm". ANSI X9.31-1 specifies a
digital signature mechanism with appendix using the RSA public
key technique.
- ANSI X9.30-1 (1997) [X9.30-1]: "Public Key Cryptography Using
Irreversible Algorithms for the Financial Services Industry -
Part 1: The Digital Signature Algorithm (DSA)". ANSI X9.30-1
specifies the DSA, NIST's Digital Signature Algorithm.
- ANSI X9.62 (1998) [X9.62]: "Public Key Cryptography for the
Financial Services Industry - The Elliptic Curve Digital
Signature Algorithm (ECDSA)". ANSI X9.62 specifies the Elliptic
Curve Digital Signature Algorithm, an analog of NIST's Digital
Signature Algorithm (DSA) using elliptic curves. The appendices
provide tutorial information on the underlying mathematics for
elliptic curve cryptography and give many examples.
Annex J (Informative): Guidance on Naming
J.1. Allocation of Names
The subject name shall be allocated through a registration scheme
administered through a Registration Authority (RA) to ensure
uniqueness. This RA may be an independent body or a function carried
out by the Certification Authority.
In addition to ensuring uniqueness, the RA shall verify that the name
allocated properly identifies the applicant and that authentication
checks are carried out to protect against masquerade.
The name allocated by an RA is based on registration information
provided by, or relating to, the applicant (e.g., his personal name,
date of birth, residence address) and information allocated by the
RA. Three variations commonly exist:
- the name is based entirely on registration information, which
uniquely identifies the applicant (e.g., "Pierre Durand (born
on) July 6, 1956");
- the name is based on registration information, with the addition
of qualifiers added by the registration authority to ensure
uniqueness (e.g., "Pierre Durand 12");
- the registration information is kept private by the registration
authority and the registration authority allocates a
"pseudonym".
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J.2. Providing Access to Registration Information
Under certain circumstances, it may be necessary for information used
during registration, but not published in the certificate, to be made
available to third parties (e.g., to an arbitrator to resolve a
dispute or for law enforcement). This registration information is
likely to include personal and sensitive information.
Thus, the RA needs to establish a policy for:
- whether the registration information should be disclosed;
- to whom such information should be disclosed;
- under what circumstances such information should be
disclosed.
This policy may be different whether the RA is being used only within
a company or for public use. The policy will have to take into
account national legislation and in particular any data protection
and privacy legislation.
Currently, the provision of access to registration is a local matter
for the RA. However, if open access is required, standard protocols,
such as HTTP -- RFC 2068 (Internet Web Access Protocol), may be
employed with the addition of security mechanisms necessary to meet
the data protection requirements (e.g., Transport Layer Security --
RFC 4346 [RFC4346]) with client authentication.
J.3. Naming Schemes
J.3.1. Naming Schemes for Individual Citizens
In some cases, the subject name that is contained in a public key
certificate may not be meaningful enough. This may happen because of
the existence of homonyms or because of the use of pseudonyms. A
distinction could be made if more attributes were present. However,
adding more attributes to a public key certificate placed in a public
repository would be going against the privacy protection
requirements.
In any case, the Registration Authority will get information at the
time of registration, but not all that information will be placed in
the certificate. In order to achieve a balance between these two
opposite requirements, the hash values of some additional attributes
can be placed in a public key certificate. When the certificate
owner provides these additional attributes, then they can be
verified. Using biometrics attributes may unambiguously identify a
person. Examples of biometrics attributes that can be used include:
a picture or a manual signature from the certificate owner.
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NOTE: Using hash values protects privacy only if the possible
inputs are large enough. For example, using the hash of a
person's social security number is generally not sufficient since
it can easily be reversed.
A picture can be used if the verifier once met the person and later
on wants to verify that the certificate that he or she got relates to
the person whom was met. In such a case, at the first exchange, the
picture is sent, and the hash contained in the certificate may be
used by the verifier to verify that it is the right person. At the
next exchange, the picture does not need to be sent again.
A manual signature may be used if a signed document has been received
beforehand. In such a case, at the first exchange, the drawing of
the manual signature is sent, and the hash contained in the
certificate may be used by the verifier to verify that it is the
right manual signature. At the next exchange, the manual signature
does not need to be sent again.
J.3.2. Naming Schemes for Employees of an Organization
The name of an employee within an organization is likely to be some
combination of the name of the organization and the identifier of the
employee within that organization.
An organization name is usually a registered name, i.e., business or
trading name used in day-to-day business. This name is registered by
a Naming Authority, which guarantees that the organization's
registered name is unambiguous and cannot be confused with another
organization.
In order to get more information about a given registered
organization name, it is necessary to go back to a publicly available
directory maintained by the Naming Authority.
The identifier may be a name or a pseudonym (e.g., a nickname or an
employee number). When it is a name, it is supposed to be
descriptive enough to unambiguously identify the person. When it is
a pseudonym, the certificate does not disclose the identity of the
person. However, it ensures that the person has been correctly
authenticated at the time of registration and therefore may be
eligible to some advantages implicitly or explicitly obtained through
the possession of the certificate. In either case, however, this can
be insufficient because of the existence of homonyms.
Placing more attributes in the certificate may be one solution, for
example, by giving the organization unit of the person or the name of
a city where the office is located. However, the more information is
Pinkas, et al. Informational [Page 139]RFC 5126 CMS Advanced Electronic Signatures February 2008
placed in the certificate, the more problems arise if there is a
change in the organization structure or the place of work. So this
may not be the best solution. An alternative is to provide more
attributes (like the organization unit and the place of work) through
access to a directory maintained by the company. It is likely that,
at the time of registration, the Registration Authority got more
information than what was placed in the certificate, if such
additional information is placed in a repository accessible only to
the organization.
Acknowledgments
Special thanks to Russ Housley for reviewing the document.
Authors' Addresses
Denis Pinkas
Bull SAS
Rue Jean-Jaures
78340 Les Clayes sous Bois CEDEX
FRANCE
EMail: Denis.Pinkas@bull.net
Nick Pope
Thales eSecurity
Meadow View House
Long Crendon
Aylesbury
Buck
HP18 9EQ
United Kingdom
EMail: nick.pope@thales-esecurity.com
John Ross
Security & Standards Consultancy Ltd
The Waterhouse Business Centre
2 Cromer Way
Chelmsford
Essex
CM1 2QE
United Kingdom
EMail: ross@secstan.com
Pinkas, et al. Informational [Page 140]
RFC 5126 CMS Advanced Electronic Signatures February 2008
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Pinkas, et al. Informational [Page 141]
