Network Working Group J. Schaad
Request for Comments: 5272 Soaring Hawk Consulting
Obsoletes: 2797 M. Myers
Category: Standards Track TraceRoute Security, Inc.
June 2008
Certificate Management over CMS (CMC)
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
This document defines the base syntax for CMC, a Certificate
Management protocol using the Cryptographic Message Syntax (CMS).
This protocol addresses two immediate needs within the Internet
Public Key Infrastructure (PKI) community:
1. The need for an interface to public key certification products
and services based on CMS and PKCS #10 (Public Key Cryptography
Standard), and
2. The need for a PKI enrollment protocol for encryption only keys
due to algorithm or hardware design.
CMC also requires the use of the transport document and the
requirements usage document along with this document for a full
definition.
Schaad & Myers Standards Track [Page 1]RFC 5272 CMC: Structures June 2008
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Protocol Requirements . . . . . . . . . . . . . . . . . . 4
1.2. Requirements Terminology . . . . . . . . . . . . . . . . . 5
1.3. Changes since RFC 2797 . . . . . . . . . . . . . . . . . . 5
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 7
2.2. Protocol Requests/Responses . . . . . . . . . . . . . . . 9
3. PKI Requests . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1. Simple PKI Request . . . . . . . . . . . . . . . . . . . . 10
3.2. Full PKI Request . . . . . . . . . . . . . . . . . . . . . 12
3.2.1. PKIData Content Type . . . . . . . . . . . . . . . . . 13
3.2.1.1. Control Syntax . . . . . . . . . . . . . . . . . . 14
3.2.1.2. Certification Request Formats . . . . . . . . . . 15
3.2.1.2.1. PKCS #10 Certification Syntax . . . . . . . . 16
3.2.1.2.2. CRMF Certification Syntax . . . . . . . . . . 17
3.2.1.2.3. Other Certification Request . . . . . . . . . 18
3.2.1.3. Content Info Objects . . . . . . . . . . . . . . . 19
3.2.1.3.1. Authenticated Data . . . . . . . . . . . . . . 19
3.2.1.3.2. Data . . . . . . . . . . . . . . . . . . . . . 20
3.2.1.3.3. Enveloped Data . . . . . . . . . . . . . . . . 20
3.2.1.3.4. Signed Data . . . . . . . . . . . . . . . . . 20
3.2.1.4. Other Message Bodies . . . . . . . . . . . . . . . 21
3.2.2. Body Part Identification . . . . . . . . . . . . . . . 21
3.2.3. CMC Unsigned Data Attribute . . . . . . . . . . . . . 22
4. PKI Responses . . . . . . . . . . . . . . . . . . . . . . . . 23
4.1. Simple PKI Response . . . . . . . . . . . . . . . . . . . 23
4.2. Full PKI Response . . . . . . . . . . . . . . . . . . . . 24
4.2.1. PKIResponse Content Type . . . . . . . . . . . . . . . 24
5. Application of Encryption to a PKI Request/Response . . . . . 25
6. Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.1. CMC Status Info Controls . . . . . . . . . . . . . . . . . 28
6.1.1. Extended CMC Status Info Control . . . . . . . . . . . 28
6.1.2. CMC Status Info Control . . . . . . . . . . . . . . . 30
6.1.3. CMCStatus Values . . . . . . . . . . . . . . . . . . . 31
6.1.4. CMCFailInfo . . . . . . . . . . . . . . . . . . . . . 32
6.2. Identification and Identity Proof Controls . . . . . . . . 33
6.2.1. Identity Proof Version 2 Control . . . . . . . . . . . 33
6.2.2. Identity Proof Control . . . . . . . . . . . . . . . . 35
6.2.3. Identification Control . . . . . . . . . . . . . . . . 35
6.2.4. Hardware Shared-Secret Token Generation . . . . . . . 36
6.3. Linking Identity and POP Information . . . . . . . . . . . 36
6.3.1. Cryptographic Linkage . . . . . . . . . . . . . . . . 37
6.3.1.1. POP Link Witness Version 2 Controls . . . . . . . 37
6.3.1.2. POP Link Witness Control . . . . . . . . . . . . . 38
6.3.1.3. POP Link Random Control . . . . . . . . . . . . . 38
6.3.2. Shared-Secret/Subject DN Linking . . . . . . . . . . . 39
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6.3.3. Renewal and Rekey Messages . . . . . . . . . . . . . . 39
6.4. Data Return Control . . . . . . . . . . . . . . . . . . . 40
6.5. RA Certificate Modification Controls . . . . . . . . . . . 40
6.5.1. Modify Certification Request Control . . . . . . . . . 41
6.5.2. Add Extensions Control . . . . . . . . . . . . . . . . 42
6.6. Transaction Identifier Control and Sender and
Recipient Nonce Controls . . . . . . . . . . . . . . . . . 44
6.7. Encrypted and Decrypted POP Controls . . . . . . . . . . . 45
6.8. RA POP Witness Control . . . . . . . . . . . . . . . . . . 48
6.9. Get Certificate Control . . . . . . . . . . . . . . . . . 49
6.10. Get CRL Control . . . . . . . . . . . . . . . . . . . . . 49
6.11. Revocation Request Control . . . . . . . . . . . . . . . . 50
6.12. Registration and Response Information Controls . . . . . . 52
6.13. Query Pending Control . . . . . . . . . . . . . . . . . . 53
6.14. Confirm Certificate Acceptance Control . . . . . . . . . . 53
6.15. Publish Trust Anchors Control . . . . . . . . . . . . . . 54
6.16. Authenticated Data Control . . . . . . . . . . . . . . . . 55
6.17. Batch Request and Response Controls . . . . . . . . . . . 56
6.18. Publication Information Control . . . . . . . . . . . . . 57
6.19. Control Processed Control . . . . . . . . . . . . . . . . 58
7. Registration Authorities . . . . . . . . . . . . . . . . . . . 59
7.1. Encryption Removal . . . . . . . . . . . . . . . . . . . . 60
7.2. Signature Layer Removal . . . . . . . . . . . . . . . . . 61
8. Security Considerations . . . . . . . . . . . . . . . . . . . 61
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 62
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 63
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 63
11.1. Normative References . . . . . . . . . . . . . . . . . . . 63
11.2. Informative References . . . . . . . . . . . . . . . . . . 63
Appendix A. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 65
Appendix B. Enrollment Message Flows . . . . . . . . . . . . . . 74
B.1. Request of a Signing Certificate . . . . . . . . . . . . . 74
B.2. Single Certification Request, But Modified by RA . . . . . 75
B.3. Direct POP for an RSA Certificate . . . . . . . . . . . . 78
Appendix C. Production of Diffie-Hellman Public Key
Certification Requests . . . . . . . . . . . . . . . 81
C.1. No-Signature Signature Mechanism . . . . . . . . . . . . . 81
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1. Introduction
This document defines the base syntax for CMC, a Certificate
Management protocol using the Cryptographic Message Syntax (CMS).
This protocol addresses two immediate needs within the Internet PKI
community:
1. The need for an interface to public key certification products
and services based on CMS and PKCS #10, and
2. The need for a PKI enrollment protocol for encryption only keys
due to algorithm or hardware design.
A small number of additional services are defined to supplement the
core certification request service.
1.1. Protocol Requirements
The protocol must be based as much as possible on the existing CMS,
PKCS #10 [PKCS10] and CRMF (Certificate Request Message Format)
[CRMF] specifications.
The protocol must support the current industry practice of a PKCS #10
certification request followed by a PKCS#7 "certs-only" response as a
subset of the protocol.
The protocol must easily support the multi-key enrollment protocols
required by S/MIME and other groups.
The protocol must supply a way of doing all enrollment operations in
a single round-trip. When this is not possible the number of
round-trips is to be minimized.
The protocol must be designed such that all key generation can occur
on the client.
Support must exist for the mandatory algorithms used by S/MIME.
Support should exist for all other algorithms cited by the S/MIME
core documents.
The protocol must contain Proof-of-Possession (POP) methods.
Optional provisions for multiple-round-trip POP will be made if
necessary.
The protocol must support deferred and pending responses to
enrollment requests for cases where external procedures are required
to issue a certificate.
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The protocol must support arbitrary chains of Registration
Authorities (RAs) as intermediaries between certification requesters
and Certification Authorities (CAs).
1.2. Requirements Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
1.3. Changes since RFC 2797
We have done a major overhaul on the layout of the document. This
included two different steps. Firstly we removed some sections from
the document and moved them to two other documents. Information on
how to transport our messages are now found in [CMC-TRANS].
Information on which controls and sections of this document must be
implemented along with which algorithms are required can now be found
in [CMC-COMPL].
A number of new controls have been added in this version:
Extended CMC Status Info Section 6.1.1
Publish Trust Anchors Section 6.15
Authenticate Data Section 6.16
Batch Request and Response Processing Section 6.17
Publication Information Section 6.18
Modify Certification Request Section 6.5.1
Control Processed Section 6.19
Identity Proof Section 6.2.2
Identity POP Link Witness V2 Section 6.3.1.1
2. Protocol Overview
A PKI enrollment transaction in this specification is generally
composed of a single round-trip of messages. In the simplest case a
PKI enrollment request, henceforth referred to as a PKI Request, is
sent from the client to the server and a PKI enrollment response,
henceforth referred to as a PKI Response, is then returned from the
Schaad & Myers Standards Track [Page 5]RFC 5272 CMC: Structures June 2008
server to the client. In more complicated cases, such as delayed
certificate issuance, more than one round-trip is required.
This specification defines two PKI Request types and two PKI Response
types.
PKI Requests are formed using either the PKCS #10 or CRMF structure.
The two PKI Requests are:
Simple PKI Request: the bare PKCS #10 (in the event that no other
services are needed), and
Full PKI Request: one or more PKCS #10, CRMF or Other Request
Messages structures wrapped in a CMS encapsulation as part of a
PKIData.
PKI Responses are based on SignedData or AuthenticatedData [CMS].
The two PKI Responses are
Simple PKI Response: a "certs-only" SignedData (in the event no
other services are needed), or
Full PKI Response: a PKIResponse content type wrapped in a
SignedData.
No special services are provided for either renewal (i.e., a new
certificate with the same key) or rekey (i.e., a new certificate with
a new key) of client certificates. Instead renewal and rekey
requests look the same as any certification request, except that the
identity proof is supplied by existing certificates from a trusted
CA. (This is usually the same CA, but could be a different CA in the
same organization where naming is shared.)
No special services are provided to distinguish between a rekey
request and a new certification request (generally for a new
purpose). A control to unpublish a certificate would normally be
included in a rekey request, and be omitted in a new certification
request. CAs or other publishing agents are also expected to have
policies for removing certificates from publication either based on
new certificates being added or the expiration or revocation of a
certificate.
A provision exists for RAs to participate in the protocol by taking
PKI Requests, wrapping them in a second layer of PKI Request with
additional requirements or statements from the RA and then passing
this new expanded PKI Request on to the CA.
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This specification makes no assumptions about the underlying
transport mechanism. The use of CMS does not imply an email-based
transport. Several different possible transport methods are defined
in [CMC-TRANS].
Optional services available through this specification are
transaction management, replay detection (through nonces), deferred
certificate issuance, certificate revocation requests and
certificate/certificate revocation list (CRL) retrieval.
2.1. Terminology
There are several different terms, abbreviations, and acronyms used
in this document. These are defined here, in no particular order,
for convenience and consistency of usage:
End-Entity (EE) refers to the entity that owns a key pair and for
whom a certificate is issued.
Registration Authority (RA) or Local RA (LRA) refers to an entity
that acts as an intermediary between the EE and the CA. Multiple
RAs can exist between the end-entity and the Certification
Authority. RAs may perform additional services such as key
generation or key archival. This document uses the term RA for
both RA and LRA.
Certification Authority (CA) refers to the entity that issues
certificates.
Client refers to an entity that creates a PKI Request. In this
document, both RAs and EEs can be clients.
Server refers to the entities that process PKI Requests and create
PKI Responses. In this document, both CAs and RAs can be servers.
PKCS #10 refers to the Public Key Cryptography Standard #10
[PKCS10], which defines a certification request syntax.
CRMF refers to the Certificate Request Message Format RFC [CRMF].
CMC uses this certification request syntax defined in this
document as part of the protocol.
CMS refers to the Cryptographic Message Syntax RFC [CMS]. This
document provides for basic cryptographic services including
encryption and signing with and without key management.
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PKI Request/Response refers to the requests/responses described in
this document. PKI Requests include certification requests,
revocation requests, etc. PKI Responses include certs-only
messages, failure messages, etc.
Proof-of-Identity refers to the client proving they are who they say
that they are to the server.
Enrollment or certification request refers to the process of a
client requesting a certificate. A certification request is a
subset of the PKI Requests.
Proof-of-Possession (POP) refers to a value that can be used to
prove that the private key corresponding to a public key is in the
possession and can be used by an end-entity. The different types
of POP are:
Signature provides the required POP by a signature operation over
some data.
Direct provides the required POP operation by an encrypted
challenge/response mechanism.
Indirect provides the required POP operation by returning the
issued certificate in an encrypted state. (This method is not
used by CMC.)
Publish provides the required POP operation by providing the
private key to the certificate issuer. (This method is not
currently used by CMC. It would be used by Key Generation or
Key Escrow extensions.)
Attested provides the required POP operation by allowing a
trusted entity to assert that the POP has been proven by one of
the above methods.
Object IDentifier (OID) is a primitive type in Abstract Syntax
Notation One (ASN.1).
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2.2. Protocol Requests/Responses
Figure 1 shows the Simple PKI Requests and Responses. The contents
of Simple PKI Request and Response are detailed in Sections 3.1 and
4.1.
Simple PKI Request Simple PKI Response
------------------------- --------------------------
+----------+ +------------------+
| PKCS #10 | | CMS ContentInfo |
+----------+--------------+ +------------------+------+
| Certification Request | | CMS Signed Data, |
| | | no SignerInfo |
| Subject Name | |
| Subject Public Key Info | | SignedData contains one |
| (K_PUB) | | or more certificates in |
| Attributes | | the certificates field |
| | | Relevant CA certs and |
+-----------+-------------+ | CRLs can be included |
| signed with | | as well. |
| matching | | |
| K_PRIV | | encapsulatedContentInfo |
+-------------+ | is absent. |
+--------------+----------+
| unsigned |
+----------+
Figure 1: Simple PKI Requests and Responses
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Figure 2 shows the Full PKI Requests and Responses. The contents of
the Full PKI Request and Response are detailed in Sections 3.2 and
4.2.
Full PKI Request Full PKI Response
----------------------- ------------------------
+----------------+ +----------------+
| CMS ContentInfo| | CMS ContentInfo|
| CMS SignedData | | CMS SignedData |
| or Auth Data | | or Auth Data |
| object | | object |
+----------------+--------+ +----------------+--------+
| | | |
| PKIData | | PKIResponseBody |
| | | |
| Sequence of: | | Sequence of: |
| <enrollment control>* | | <enrollment control>* |
| <certification request>*| | <CMS object>* |
| <CMS object>* | | <other message>* |
| <other message>* | | |
| | | where * == zero or more |
| where * == zero or more | | |
| | | All certificates issued |
| Certification requests | | as part of the response |
| are CRMF, PKCS #10, or | | are included in the |
| Other. | | "certificates" field |
| | | of the SignedData. |
+-------+-----------------+ | Relevant CA certs and |
| signed (keypair | | CRLs can be included as |
| used may be pre-| | well. |
| existing or | | |
| identified in | +---------+---------------+
| the request) | | signed by the |
+-----------------+ | CA or an LRA |
+---------------+
Figure 2: Full PKI Requests and Responses
3. PKI Requests
Two types of PKI Requests exist. This section gives the details for
both types.
3.1. Simple PKI Request
A Simple PKI Request uses the PKCS #10 syntax CertificationRequest
[PKCS10].
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When a server processes a Simple PKI Request, the PKI Response
returned is:
Simple PKI Response on success.
Full PKI Response on failure. The server MAY choose not to return a
PKI Response in this case.
The Simple PKI Request MUST NOT be used if a proof-of-identity needs
to be included.
The Simple PKI Request cannot be used if the private key is not
capable of producing some type of signature (i.e., Diffie-Hellman
(DH) keys can use the signature algorithms in [DH-POP] for production
of the signature).
The Simple PKI Request cannot be used for any of the advanced
services specified in this document.
The client MAY incorporate one or more X.509v3 extensions in any
certification request based on PKCS #10 as an ExtensionReq attribute.
The ExtensionReq attribute is defined as:
ExtensionReq ::= SEQUENCE SIZE (1..MAX) OF Extension
where Extension is imported from [PKIXCERT] and ExtensionReq is
identified by:
id-ExtensionReq OBJECT IDENTIFIER ::= {iso(1) member-body(2) us(840)
rsadsi(113549) pkcs(1) pkcs-9(9) 14}
Servers MUST be able to process all extensions defined, but not
prohibited, in [PKIXCERT]. Servers are not required to be able to
process other X.509v3 extensions transmitted using this protocol, nor
are they required to be able to process private extensions. Servers
are not required to put all client-requested extensions into a
certificate. Servers are permitted to modify client-requested
extensions. Servers MUST NOT alter an extension so as to invalidate
the original intent of a client-requested extension. (For example,
changing key usage from keyAgreement to digitalSignature.) If a
certification request is denied due to the inability to handle a
requested extension and a PKI Response is returned, the server MUST
return a PKI Response with a CMCFailInfo value with the value
unsupportedExt.
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3.2. Full PKI Request
The Full PKI Request provides the most functionality and flexibility.
The Full PKI Request is encapsulated in either a SignedData or an
AuthenticatedData with an encapsulated content type of id-cct-PKIData
(Section 3.2.1).
When a server processes a Full PKI Request, a PKI Response MUST be
returned. The PKI Response returned is:
Simple PKI Response if the enrollment was successful and only
certificates are returned. (A CMCStatusInfoV2 control with
success is implied.)
Full PKI Response if the enrollment was successful and information
is returned in addition to certificates, if the enrollment is
pending, or if the enrollment failed.
If SignedData is used, the signature can be generated using either
the private key material of an embedded signature certification
request (i.e., included in the TaggedRequest tcr or crm fields) or a
previously certified signature key. If the private key of a
signature certification request is used, then:
a. The certification request containing the corresponding public key
MUST include a Subject Key Identifier extension.
b. The subjectKeyIdentifier form of the signerIdentifier in
SignerInfo MUST be used.
c. The value of the subjectKeyIdentifier form of SignerInfo MUST be
the Subject Key Identifier specified in the corresponding
certification request. (The subjectKeyIdentifier form of
SignerInfo is used here because no certificates have yet been
issued for the signing key.) If the request key is used for
signing, there MUST be only one SignerInfo in the SignedData.
If AuthenticatedData is used, then:
a. The Password Recipient Info option of RecipientInfo MUST be used.
b. A randomly generated key is used to compute the Message
Authentication Code (MAC) value on the encapsulated content.
c. The input for the key derivation algorithm is a concatenation of
the identifier (encoded as UTF8) and the shared-secret.
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When creating a PKI Request to renew or rekey a certificate:
a. The Identification and Identity Proof controls are absent. The
same information is provided by the use of an existing
certificate from a CA when signing the PKI Request. In this
case, the CA that issued the original certificate and the CA the
request is made to will usually be the same, but could have a
common operator.
b. CAs and RAs can impose additional restrictions on the signing
certificate used. They may require that the most recently issued
signing certificate for a client be used.
c. Some CAs may prevent renewal operations (i.e., reuse of the same
keys). In this case the CA MUST return a PKI Response with
noKeyReuse as the CMCFailInfo failure code.
3.2.1. PKIData Content Type
The PKIData content type is used for the Full PKI Request. A PKIData
content type is identified by:
id-cct-PKIData ::= {id-pkix id-cct(12) 2 }
The ASN.1 structure corresponding to the PKIData content type is:
PKIData ::= SEQUENCE {
controlSequence SEQUENCE SIZE(0..MAX) OF TaggedAttribute,
reqSequence SEQUENCE SIZE(0..MAX) OF TaggedRequest,
cmsSequence SEQUENCE SIZE(0..MAX) OF TaggedContentInfo,
otherMsgSequence SEQUENCE SIZE(0..MAX) OF OtherMsg
}
The fields in PKIData have the following meaning:
controlSequence is a sequence of controls. The controls defined in
this document are found in Section 6. Controls can be defined by
other parties. Details on the TaggedAttribute structure can be
found in Section 3.2.1.1.
reqSequence is a sequence of certification requests. The
certification requests can be a CertificationRequest (PKCS #10), a
CertReqMsg (CRMF), or an externally defined PKI request. Full
details are found in Section 3.2.1.2. If an externally defined
certification request is present, but the server does not
understand the certification request (or will not process it), a
CMCStatus of noSupport MUST be returned for the certification
request item and no other certification requests are processed.
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cmsSequence is a sequence of [CMS] message objects. See
Section 3.2.1.3 for more details.
otherMsgSequence is a sequence of arbitrary data objects. Data
objects placed here are referred to by one or more controls. This
allows for controls to use large amounts of data without the data
being embedded in the control. See Section 3.2.1.4 for more
details.
All certification requests encoded into a single PKIData SHOULD be
for the same identity. RAs that batch process (see Section 6.17) are
expected to place the PKI Requests received into the cmsSequence of a
PKIData.
Processing of the PKIData by a recipient is as follows:
1. All controls should be examined and processed in an appropriate
manner. The appropriate processing is to complete processing at
this time, to ignore the control, or to place the control on a
to-do list for later processing. Controls can be processed in
any order; the order in the sequence is not significant.
2. Items in the reqSequence are not referenced by a control. These
items, which are certification requests, also need to be
processed. As with controls, the appropriate processing can be
either immediate processing or addition to a to-do list for later
processing.
3. Finally, the to-do list is processed. In many cases, the to-do
list will be ordered by grouping specific tasks together.
No processing is required for cmsSequence or otherMsgSequence members
of PKIData if they are present and are not referenced by a control.
In this case, the cmsSequence and otherMsgSequence members are
ignored.
3.2.1.1. Control Syntax
The actions to be performed for a PKI Request/Response are based on
the included controls. Each control consists of an object identifier
and a value based on the object identifier.
Schaad & Myers Standards Track [Page 14]RFC 5272 CMC: Structures June 2008
The syntax of a control is:
TaggedAttribute ::= SEQUENCE {
bodyPartID BodyPartID,
attrType OBJECT IDENTIFIER,
attrValues SET OF AttributeValue
}
AttributeValue ::= ANY
The fields in TaggedAttribute have the following meaning:
bodyPartID is a unique integer that identifies this control.
attrType is the OID that identifies the control.
attrValues is the data values used in processing the control. The
structure of the data is dependent on the specific
control.
The final server MUST fail the processing of an entire PKIData if any
included control is not recognized, that control is not already
marked as processed by a Control Processed control (see Section 6.19)
and no other error is generated. The PKI Response MUST include a
CMCFailInfo value with the value badRequest and the bodyList MUST
contain the bodyPartID of the invalid or unrecognized control(s). A
server is the final server if and only if it is not passing the PKI
Request on to another server. A server is not considered to be the
final server if the server would have passed the PKI Request on, but
instead it returned a processing error.
The controls defined by this document are found in Section 6.
3.2.1.2. Certification Request Formats
Certification Requests are based on PKCS #10, CRMF, or Other Request
formats. Section 3.2.1.2.1 specifies the requirements for clients
and servers dealing with PKCS #10. Section 3.2.1.2.2 specifies the
requirements for clients and servers dealing with CRMF.
Section 3.2.1.2.3 specifies the requirements for clients and servers
dealing with Other Request.
Schaad & Myers Standards Track [Page 15]RFC 5272 CMC: Structures June 2008
TaggedRequest ::= CHOICE {
tcr [0] TaggedCertificationRequest,
crm [1] CertReqMsg,
orm [2] SEQUENCE {
bodyPartID BodyPartID,
requestMessageType OBJECT IDENTIFIER,
requestMessageValue ANY DEFINED BY requestMessageType
}
}
The fields in TaggedRequest have the following meaning:
tcr is a certification request that uses the PKCS #10 syntax.
Details on PKCS #10 are found in Section 3.2.1.2.1.
crm is a certification request that uses the CRMF syntax. Details
on CRMF are found in Section 3.2.1.2.2.
orm is an externally defined certification request. One example is
an attribute certification request. The fields of this structure
are:
bodyPartID is the identifier number for this certification
request. Details on body part identifiers are found in
Section 3.2.2.
requestMessageType identifies the other request type. These
values are defined outside of this document.
requestMessageValue is the data associated with the other request
type.
3.2.1.2.1. PKCS #10 Certification Syntax
A certification request based on PKCS #10 uses the following ASN.1
structure:
TaggedCertificationRequest ::= SEQUENCE {
bodyPartID BodyPartID,
certificationRequest CertificationRequest
}
The fields in TaggedCertificationRequest have the following meaning:
bodyPartID is the identifier number for this certification request.
Details on body part identifiers are found in Section 3.2.2.
Schaad & Myers Standards Track [Page 16]RFC 5272 CMC: Structures June 2008
certificationRequest contains the PKCS-#10-based certification
request. Its fields are described in [PKCS10].
When producing a certification request based on PKCS #10, clients
MUST produce the certification request with a subject name and public
key. Some PKI products are operated using a central repository of
information to assign subject names upon receipt of a certification
request. To accommodate this mode of operation, the subject field in
a CertificationRequest MAY be NULL, but MUST be present. CAs that
receive a CertificationRequest with a NULL subject field MAY reject
such certification requests. If rejected and a PKI Response is
returned, the CA MUST return a PKI Response with the CMCFailInfo
value with the value badRequest.
3.2.1.2.2. CRMF Certification Syntax
A CRMF message uses the following ASN.1 structure (defined in [CRMF]
and included here for convenience):
CertReqMsg ::= SEQUENCE {
certReq CertRequest,
popo ProofOfPossession OPTIONAL,
-- content depends upon key type
regInfo SEQUENCE SIZE(1..MAX) OF AttributeTypeAndValue OPTIONAL }
CertRequest ::= SEQUENCE {
certReqId INTEGER, -- ID for matching request and reply
certTemplate CertTemplate, --Selected fields of cert to be issued
controls Controls OPTIONAL } -- Attributes affecting issuance
CertTemplate ::= SEQUENCE {
version [0] Version OPTIONAL,
serialNumber [1] INTEGER OPTIONAL,
signingAlg [2] AlgorithmIdentifier OPTIONAL,
issuer [3] Name OPTIONAL,
validity [4] OptionalValidity OPTIONAL,
subject [5] Name OPTIONAL,
publicKey [6] SubjectPublicKeyInfo OPTIONAL,
issuerUID [7] UniqueIdentifier OPTIONAL,
subjectUID [8] UniqueIdentifier OPTIONAL,
extensions [9] Extensions OPTIONAL }
The fields in CertReqMsg are explained in [CRMF].
Schaad & Myers Standards Track [Page 17]RFC 5272 CMC: Structures June 2008
This document imposes the following additional restrictions on the
construction and processing of CRMF certification requests:
When a Full PKI Request includes a CRMF certification request,
both the subject and publicKey fields in the CertTemplate MUST be
defined. The subject field can be encoded as NULL, but MUST be
present.
When both CRMF and CMC controls exist with equivalent
functionality, the CMC control SHOULD be used. The CMC control
MUST override the CRMF control.
The regInfo field MUST NOT be used on a CRMF certification
request. Equivalent functionality is provided in the CMC regInfo
control (Section 6.12).
The indirect method of proving POP is not supported in this
protocol. One of the other methods (including the direct method
described in this document) MUST be used. The value of encrCert
in SubsequentMessage MUST NOT be used.
Since the subject and publicKeyValues are always present, the
POPOSigningKeyInput MUST NOT be used when computing the value for
POPSigningKey.
A server is not required to use all of the values suggested by the
client in the CRMF certification request. Servers MUST be able to
process all extensions defined, but not prohibited in [PKIXCERT].
Servers are not required to be able to process other X.509v3
extensions transmitted using this protocol, nor are they required to
be able to process private extensions. Servers are permitted to
modify client-requested extensions. Servers MUST NOT alter an
extension so as to invalidate the original intent of a client-
requested extension. (For example, change key usage from
keyAgreement to digitalSignature.) If a certification request is
denied due to the inability to handle a requested extension, the
server MUST respond with a Full PKI Response with a CMCFailInfo value
with the value of unsupportedExt.
3.2.1.2.3. Other Certification Request
This document allows for other certification request formats to be
defined and used as well. An example of an other certification
request format is one for Attribute Certificates. These other
certification request formats are defined by specifying an OID for
identification and the structure to contain the data to be passed.
Schaad & Myers Standards Track [Page 18]RFC 5272 CMC: Structures June 2008
3.2.1.3. Content Info Objects
The cmsSequence field of the PKIData and PKIResponse messages
contains zero or more tagged content info objects. The syntax for
this structure is:
TaggedContentInfo ::= SEQUENCE {
bodyPartID BodyPartID,
contentInfo ContentInfo
}
The fields in TaggedContentInfo have the following meaning:
bodyPartID is a unique integer that identifies this content info
object.
contentInfo is a ContentInfo object (defined in [CMS]).
The four content types used in cmsSequence are AuthenticatedData,
Data, EnvelopedData, and SignedData. All of these content types are
defined in [CMS].
3.2.1.3.1. Authenticated Data
The AuthenticatedData content type provides a method of doing pre-
shared-secret-based validation of data being sent between two
parties. Unlike SignedData, it does not specify which party actually
generated the information.
AuthenticatedData provides origination authentication in those
circumstances where a shared-secret exists, but a PKI-based trust has
not yet been established. No PKI-based trust may have been
established because a trust anchor has not been installed on the
client or no certificate exists for a signing key.
AuthenticatedData content type is used by this document for:
The id-cmc-authData control (Section 6.16), and
The top-level wrapper in environments where an encryption-only key
is being certified.
This content type can include both PKIData and PKIResponse as the
encapsulated content types. These embedded content types can contain
additional controls that need to be processed.
Schaad & Myers Standards Track [Page 19]RFC 5272 CMC: Structures June 2008
3.2.1.3.2. Data
The Data content type allows for general transport of unstructured
data.
The Data content type is used by this document for:
Holding the encrypted random value y for POP proof in the
encrypted POP control (see Section 6.7).
3.2.1.3.3. Enveloped Data
The EnvelopedData content type provides for shrouding of data.
The EnvelopedData content type is the primary confidentiality method
for sensitive information in this protocol. EnvelopedData can
provide encryption of an entire PKI Request (see Section 5).
EnvelopedData can also be used to wrap private key material for key
archival. If the decryption on an EnvelopedData fails, a Full PKI
Response is returned with a CMCFailInfo value of badMessageCheck and
a bodyPartID of 0.
3.2.1.3.4. Signed Data
The SignedData content type provides for authentication and
integrity.
The SignedData content type is used by this document for:
The outer wrapper for a PKI Request.
The outer wrapper for a PKI Response.
As part of processing a PKI Request/Response, the signature(s) MUST
be verified. If the signature does not verify and the PKI Request/
Response contains anything other than a CMC Status Info control, a
Full PKI Response containing a CMC Status Info control MUST be
returned using a CMCFailInfo with a value of badMessageCheck and a
bodyPartID of 0.
For the PKI Response, SignedData allows the server to sign the
returning data, if any exists, and to carry the certificates and CRLs
corresponding to the PKI Request. If no data is being returned
beyond the certificates and CRLs, the EncapsulatedInfo and SignerInfo
fields are not populated.
Schaad & Myers Standards Track [Page 20]RFC 5272 CMC: Structures June 2008
3.2.1.4. Other Message Bodies
The otherMsgSequence field of the PKI Request/Response allows for
arbitrary data objects to be carried as part of a PKI Request/
Response. This is intended to contain a data object that is not
already wrapped in a cmsSequence field (Section 3.2.1.3). The data
object is ignored unless a control references the data object by
bodyPartID.
OtherMsg ::= SEQUENCE {
bodyPartID BodyPartID,
otherMsgType OBJECT IDENTIFIER,
otherMsgValue ANY DEFINED BY otherMsgType }
The fields in OtherMsg have the following meaning:
bodyPartID is the unique id identifying this data object.
otherMsgType is the OID that defines the type of message body.
otherMsgValue is the data.
3.2.2. Body Part Identification
Each element of a PKIData or PKIResponse has an associated body part
identifier. The body part identifier is a 4-octet integer using the
ASN.1 of:
bodyIdMax INTEGER ::= 4294967295
BodyPartID ::= INTEGER(0..bodyIdMax)
Body part identifiers are encoded in the certReqIds field for
CertReqMsg objects (in a TaggedRequest) or in the bodyPartID field of
the other objects. The body part identifier MUST be unique within a
single PKIData or PKIResponse. Body part identifiers can be
duplicated in different layers (for example, a PKIData embedded
within another).
The bodyPartID value of 0 is reserved for use as the reference to the
current PKIData object.
Some controls, such as the Add Extensions control (Section 6.5.2),
use the body part identifier in the pkiDataReference field to refer
to a PKI Request in the current PKIData. Some controls, such as the
Extended CMC Status Info control (Section 6.1.1), will also use body
part identifiers to refer to elements in the previous PKI Request/
Schaad & Myers Standards Track [Page 21]RFC 5272 CMC: Structures June 2008
Response. This allows an error to be explicit about the control or
PKI Request to which the error applies.
A BodyPartList contains a list of body parts in a PKI Request/
Response (i.e., the Batch Request control in Section 6.17). The
ASN.1 type BodyPartList is defined as:
BodyPartList ::= SEQUENCE SIZE (1..MAX) OF BodyPartID
A BodyPartPath contains a path of body part identifiers moving
through nesting (i.e., the Modify Certification Request control in
Section 6.5.1). The ASN.1 type BodyPartPath is defined as:
BodyPartPath ::= SEQUENCE SIZE (1..MAX) OF BodyPartID
3.2.3. CMC Unsigned Data Attribute
There is sometimes a need to include data in a PKI Request designed
to be removed by an RA during processing. An example of this is the
inclusion of an encrypted private key, where a Key Archive Agent
removes the encrypted private key before sending it on to the CA.
One side effect of this desire is that every RA that encapsulates
this information needs to move the data so that it is not covered by
that RA's signature. (A client PKI Request encapsulated by an RA
cannot have a signed control removed by the Key Archive Agent without
breaking the RA's signature.) The CMC Unsigned Data attribute
addresses this problem.
The CMC Unsigned Data attribute contains information that is not
directly signed by a client. When an RA encounters this attribute in
the unsigned or unauthenticated attribute field of a request it is
aggregating, the CMC Unsigned Data attribute is removed from the
request prior to placing the request in a cmsSequence and placed in
the unsigned or unauthenticated attributes of the RA's signed or
authenticated data wrapper.
The CMC Unsigned Data attribute is identified by:
id-aa-cmc-unsignedData OBJECT IDENTIFIER ::= {id-aa 34}
The CMC Unsigned Data attribute has the ASN.1 definition:
CMCUnsignedData ::= SEQUENCE {
bodyPartPath BodyPartPath,
identifier OBJECT IDENTIFIER,
content ANY DEFINED BY identifier
}
Schaad & Myers Standards Track [Page 22]RFC 5272 CMC: Structures June 2008
The fields in CMCUnsignedData have the following meaning:
bodyPartPath is the path pointing to the control associated with
this data. When an RA moves the control in an unsigned or
unauthenticated attribute up one level as part of wrapping the
data in a new SignedData or AuthenticatedData, the body part
identifier of the embedded item in the PKIData is prepended to the
bodyPartPath sequence.
identifier is the OID that defines the associated data.
content is the data.
There MUST be at most one CMC Unsigned Data attribute in the
UnsignedAttribute sequence of a SignerInfo or in the
UnauthenticatedAttribute sequence of an AuthenticatedData.
UnsignedAttribute consists of a set of values; the attribute can have
any number of values greater than zero in that set. If the CMC
Unsigned Data attribute is in one SignerInfo or AuthenticatedData, it
MUST appear with the same values(s) in all SignerInfo and
AuthenticatedData items.
4. PKI Responses
Two types of PKI Responses exist. This section gives the details on
both types.
4.1. Simple PKI Response
Clients MUST be able to process the Simple PKI Response. The Simple
PKI Response consists of a SignedData with no EncapsulatedContentInfo
and no SignerInfo. The certificates requested in the PKI Response
are returned in the certificate field of the SignedData.
Clients MUST NOT assume the certificates are in any order. Servers
SHOULD include all intermediate certificates needed to form complete
certification paths to one or more trust anchors, not just the newly
issued certificate(s). The server MAY additionally return CRLs in
the CRL bag. Servers MAY include the self-signed certificates.
Clients MUST NOT implicitly trust included self-signed certificate(s)
merely due to its presence in the certificate bag. In the event
clients receive a new self-signed certificate from the server,
clients SHOULD provide a mechanism to enable the user to use the
certificate as a trust anchor. (The Publish Trust Anchors control
(Section 6.15) should be used in the event that the server intends
the client to accept one or more certificates as trust anchors. This
requires the use of the Full PKI Response message.)
Schaad & Myers Standards Track [Page 23]RFC 5272 CMC: Structures June 2008
4.2. Full PKI Response
Clients MUST be able to process a Full PKI Response.
The Full PKI Response consists of a SignedData or AuthenticatedData
encapsulating a PKIResponse content type. The certificates issued in
a PKI Response are returned in the certificates field of the
immediately encapsulating SignedData.
Clients MUST NOT assume the certificates are in any order. Servers
SHOULD include all intermediate certificates needed to form complete
chains to one or more trust anchors, not just the newly issued
certificate(s). The server MAY additionally return CRLs in the CRL
bag. Servers MAY include self-signed certificates. Clients MUST NOT
implicitly trust included self-signed certificate(s) merely due to
its presence in the certificate bag. In the event clients receive a
new self-signed certificate from the server, clients MAY provide a
mechanism to enable the user to explicitly use the certificate as a
trust anchor. (The Publish Trust Anchors control (Section 6.15)
exists for the purpose of allowing for distribution of trust anchor
certificates. If a trusted anchor publishes a new trusted anchor,
this is one case where automated trust of the new trust anchor could
be allowed.)
4.2.1. PKIResponse Content Type
The PKIResponse content type is used for the Full PKI Response. The
PKIResponse content type is identified by:
id-cct-PKIResponse ::= {id-pkix id-cct(12) 3 }
The ASN.1 structure corresponding to the PKIResponse content type is:
PKIResponse ::= SEQUENCE {
controlSequence SEQUENCE SIZE(0..MAX) OF TaggedAttribute,
cmsSequence SEQUENCE SIZE(0..MAX) OF TaggedContentInfo,
otherMsgSequence SEQUENCE SIZE(0..MAX) OF OtherMsg
}
ReponseBody ::= PKIResponse
Note: In [RFC2797], this ASN.1 type was named ResponseBody. It has
been renamed to PKIResponse for clarity and the old name kept as a
synonym.
Schaad & Myers Standards Track [Page 24]RFC 5272 CMC: Structures June 2008
The fields in PKIResponse have the following meaning:
controlSequence is a sequence of controls. The controls defined in
this document are found in Section 6. Controls can be defined by
other parties. Details on the TaggedAttribute structure are found
in Section 3.2.1.1.
cmsSequence is a sequence of [CMS] message objects. See
Section 3.2.1.3 for more details.
otherMsgSequence is a sequence of arbitrary data objects. Data
objects placed here are referred to by one or more controls. This
allows for controls to use large amounts of data without the data
being embedded in the control. See Section 3.2.1.4 for more
details.
Processing of PKIResponse by a recipient is as follows:
1. All controls should be examined and processed in an appropriate
manner. The appropriate processing is to complete processing at
this time, to ignore the control, or to place the control on a
to-do list for later processing.
2. Additional processing of non-element items includes the saving of
certificates and CRLs present in wrapping layers. This type of
processing is based on the consumer of the element and should not
be relied on by generators.
No processing is required for cmsSequence or otherMsgSequence members
of the PKIResponse, if items are present and are not referenced by a
control. In this case, the cmsSequence and otherMsgSequence members
are to be ignored.
5. Application of Encryption to a PKI Request/Response
There are occasions when a PKI Request or Response must be encrypted
in order to prevent disclosure of information in the PKI Request/
Response from being accessible to unauthorized entities. This
section describes the means to encrypt Full PKI Requests and
Responses (Simple PKI Requests cannot be encrypted). Data portions
of PKI Requests and Responses that are placed in the cmsSequence
field can be encrypted separately.
Confidentiality is provided by wrapping the PKI Request/Response (a
SignedData) in an EnvelopedData. The nested content type in the
EnvelopedData is id-SignedData. Note that this is different from
S/MIME where there is a MIME layer placed between the encrypted and
signed data. It is recommended that if an EnvelopedData layer is
Schaad & Myers Standards Track [Page 25]RFC 5272 CMC: Structures June 2008
applied to a PKI Request/Response, a second signature layer be placed
outside of the EnvelopedData layer. The following figure shows how
this nesting would be done:
Normal Option 1 Option 2
------ -------- --------
SignedData EnvelopedData SignedData
PKIData SignedData EnvelopedData
PKIData SignedData
PKIData
Note: PKIResponse can be substituted for PKIData in the above figure.
Options 1 and 2 prevent leakage of sensitive data by encrypting the
Full PKI Request/Response. An RA that receives a PKI Request that it
cannot decrypt MAY reject the PKI Request unless it can process the
PKI Request without knowledge of the contents (i.e., all it does is
amalgamate multiple PKI Requests and forward them to a server).
After the RA removes the envelope and completes processing, it may
then apply a new EnvelopedData layer to protect PKI Requests for
transmission to the next processing agent. Section 7 contains more
information about RA processing.
Full PKI Requests/Responses can be encrypted or transmitted in the
clear. Servers MUST provide support for all three options.
Alternatively, an authenticated, secure channel could exist between
the parties that require confidentiality. Clients and servers MAY
use such channels instead of the technique described above to provide
secure, private communication of Simple and Full PKI Requests/
Responses.
6. Controls
Controls are carried as part of both Full PKI Requests and Responses.
Each control is encoded as a unique OID followed by the data for the
control (see syntax in Section 3.2.1.1. The encoding of the data is
based on the control. Processing systems would first detect the OID
(TaggedAttribute attrType) and process the corresponding control
value (TaggedAttribute attrValues) prior to processing the message
body.
Schaad & Myers Standards Track [Page 26]RFC 5272 CMC: Structures June 2008
The OIDs are all defined under the following arc:
id-pkix OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
dod(6) internet(1) security(5) mechanisms(5) pkix(7) }
id-cmc OBJECT IDENTIFIER ::= { id-pkix 7 }
The following table lists the names, OID, and syntactic structure for
each of the controls described in this document.
Identifier Description OID ASN.1 Structure Section
--------------------------------------------------------------------
id-cmc-statusInfo id-cmc 1 CMCStatusInfo 6.1.2
id-cmc-identification id-cmc 2 UTF8String 6.2.3
id-cmc-identityProof id-cmc 3 OCTET STRING 6.2.2
id-cmc-dataReturn id-cmc 4 OCTET STRING 6.4
id-cmc-transactionId id-cmc 5 INTEGER 6.6
id-cmc-senderNonce id-cmc 6 OCTET STRING 6.6
id-cmc-recipientNonce id-cmc 7 OCTET STRING 6.6
id-cmc-addExtensions id-cmc 8 AddExtensions 6.5.2
id-cmc-encryptedPOP id-cmc 9 EncryptedPOP 6.7
id-cmc-decryptedPOP id-cmc 10 DecryptedPOP 6.7
id-cmc-lraPOPWitness id-cmc 11 LraPOPWitness 6.8
id-cmc-getCert id-cmc 15 GetCert 6.9
id-cmc-getCRL id-cmc 16 GetCRL 6.10
id-cmc-revokeRequest id-cmc 17 RevokeRequest 6.11
id-cmc-regInfo id-cmc 18 OCTET STRING 6.12
id-cmc-responseInfo id-cmc 19 OCTET STRING 6.12
id-cmc-queryPending id-cmc 21 OCTET STRING 6.13
id-cmc-popLinkRandom id-cmc 22 OCTET STRING 6.3.1
id-cmc-popLinkWitness id-cmc 23 OCTET STRING 6.3.1
id-cmc-popLinkWitnessV2 id-cmc 33 OCTET STRING 6.3.1.1
id-cmc-confirmCertAcceptance id-cmc 24 CMCCertId 6.14
id-cmc-statusInfoV2 id-cmc 25 CMCStatusInfoV2 6.1.1
id-cmc-trustedAnchors id-cmc 26 PublishTrustAnchors 6.15
id-cmc-authData id-cmc 27 AuthPublish 6.16
id-cmc-batchRequests id-cmc 28 BodyPartList 6.17
id-cmc-batchResponses id-cmc 29 BodyPartList 6.17
id-cmc-publishCert id-cmc 30 CMCPublicationInfo 6.18
id-cmc-modCertTemplate id-cmc 31 ModCertTemplate 6.5.1
id-cmc-controlProcessed id-cmc 32 ControlsProcessed 6.19
id-cmc-identityProofV2 id-cmc 34 IdentityProofV2 6.2.1
Table 1: CMC Control Attributes
Schaad & Myers Standards Track [Page 27]RFC 5272 CMC: Structures June 2008
6.1. CMC Status Info Controls
The CMC Status Info controls return information about the status of a
client/server request/response. Two controls are described in this
section. The Extended CMC Status Info control is the preferred
control; the CMC Status Info control is included for backwards
compatibility with RFC 2797.
Servers MAY emit multiple CMC status info controls referring to a
single body part. Clients MUST be able to deal with multiple CMC
status info controls in a PKI Response. Servers MUST use the
Extended CMC Status Info control, but MAY additionally use the CMC
Status Info control. Clients MUST be able to process the Extended
CMC Status Info control.
6.1.1. Extended CMC Status Info Control
The Extended CMC Status Info control is identified by the OID:
id-cmc-statusInfoV2 ::= { id-cmc 25 }
The Extended CMC Status Info control has the ASN.1 definition:
CMCStatusInfoV2 ::= SEQUENCE {
cMCStatus CMCStatus,
bodyList SEQUENCE SIZE (1..MAX) OF BodyPartReference,
statusString UTF8String OPTIONAL,
otherInfo OtherStatusInfo OPTIONAL
}
OtherStatusInfo ::= CHOICE {
failInfo CMCFailInfo,
pendInfo PendInfo,
extendedFailInfo ExtendedFailInfo
}
PendInfo ::= SEQUENCE {
pendToken OCTET STRING,
pendTime GeneralizedTime
}
ExtendedFailInfo ::= SEQUENCE {
failInfoOID OBJECT IDENTIFIER,
failInfoValue ANY DEFINED BY failInfoOID
}
Schaad & Myers Standards Track [Page 28]RFC 5272 CMC: Structures June 2008
BodyPartReference ::= CHOICE {
bodyPartID BodyPartID,
bodyPartPath BodyPartPath
}
The fields in CMCStatusInfoV2 have the following meaning:
cMCStatus contains the returned status value. Details are in
Section 6.1.3.
bodyList identifies the controls or other elements to which the
status value applies. If an error is returned for a Simple PKI
Request, this field is the bodyPartID choice of BodyPartReference
with the single integer of value 1.
statusString contains additional description information. This
string is human readable.
otherInfo contains additional information that expands on the CMC
status code returned in the cMCStatus field.
The fields in OtherStatusInfo have the following meaning:
failInfo is described in Section 6.1.4. It provides an error code
that details what failure occurred. This choice is present only
if cMCStatus contains the value failed.
pendInfo contains information about when and how the client should
request the result of this request. It is present when the
cMCStatus is either pending or partial. pendInfo uses the
structure PendInfo, which has the fields:
pendToken is the token used in the Query Pending control
(Section 6.13).
pendTime contains the suggested time the server wants to be
queried about the status of the certification request.
extendedFailInfo includes application-dependent detailed error
information. This choice is present only if cMCStatus contains
the value failed. Caution should be used when defining new values
as they may not be correctly recognized by all clients and
servers. The CMCFailInfo value of internalCAError may be assumed
if the extended error is not recognized. This field uses the type
ExtendedFailInfo. ExtendedFailInfo has the fields:
failInfoOID contains an OID that is associated with a set of
extended error values.
Schaad & Myers Standards Track [Page 29]RFC 5272 CMC: Structures June 2008
failInfoValue contains an extended error code from the defined
set of extended error codes.
If the cMCStatus field is success, the Extended CMC Status Info
control MAY be omitted unless it is the only item in the response.
6.1.2. CMC Status Info Control
The CMC Status Info control is identified by the OID:
id-cmc-statusInfo ::= { id-cmc 1 }
The CMC Status Info control has the ASN.1 definition:
CMCStatusInfo ::= SEQUENCE {
cMCStatus CMCStatus,
bodyList BodyPartList,
statusString UTF8String OPTIONAL,
otherInfo CHOICE {
failInfo CMCFailInfo,
pendInfo PendInfo } OPTIONAL
}
The fields in CMCStatusInfo have the following meaning:
cMCStatus contains the returned status value. Details are in
Section 6.1.3.
bodyList contains the list of controls or other elements to which
the status value applies. If an error is being returned for a
Simple PKI Request, this field contains a single integer of value
1.
statusString contains additional description information. This
string is human readable.
otherInfo provides additional information that expands on the CMC
status code returned in the cMCStatus field.
failInfo is described in Section 6.1.4. It provides an error
code that details what failure occurred. This choice is
present only if cMCStatus is failed.
pendInfo uses the PendInfo ASN.1 structure in Section 6.1.1. It
contains information about when and how the client should
request results of this request. The pendInfo field MUST be
populated for a cMCStatus value of pending or partial. Further
Schaad & Myers Standards Track [Page 30]RFC 5272 CMC: Structures June 2008
details can be found in Section 6.1.1 (Extended CMC Status Info
Control) and Section 6.13 (Query Pending Control ).
If the cMCStatus field is success, the CMC Status Info control MAY be
omitted unless it is the only item in the response. If no status
exists for a Simple or Full PKI Request, then the value of success is
assumed.
6.1.3. CMCStatus Values
CMCStatus is a field in the Extended CMC Status Info and CMC Status
Info controls. This field contains a code representing the success
or failure of a specific operation. CMCStatus has the ASN.1
structure:
CMCStatus ::= INTEGER {
success (0),
-- reserved (1),
failed (2),
pending (3),
noSupport (4),
confirmRequired (5),
popRequired (6),
partial (7)
}
The values of CMCStatus have the following meaning:
success indicates the request was granted or the action was
completed.
failed indicates the request was not granted or the action was not
completed. More information is included elsewhere in the
response.
pending indicates the PKI Request has yet to be processed. The
requester is responsible to poll back on this Full PKI request.
pending may only be returned for certification request operations.
noSupport indicates the requested operation is not supported.
confirmRequired indicates a Confirm Certificate Acceptance control
(Section 6.14) must be returned before the certificate can be
used.
popRequired indicates a direct POP operation is required
(Section 6.3.1.3).
Schaad & Myers Standards Track [Page 31]RFC 5272 CMC: Structures June 2008
partial indicates a partial PKI Response is returned. The requester
is responsible to poll back for the unfulfilled portions of the
Full PKI Request.
6.1.4. CMCFailInfo
CMCFailInfo is a field in the Extended CMC Status Info and CMC Status
Info controls. CMCFailInfo conveys more detailed information
relevant to the interpretation of a failure condition. The
CMCFailInfo has the following ASN.1 structure:
CMCFailInfo ::= INTEGER {
badAlg (0),
badMessageCheck (1),
badRequest (2),
badTime (3),
badCertId (4),
unsupportedExt (5),
mustArchiveKeys (6),
badIdentity (7),
popRequired (8),
popFailed (9),
noKeyReuse (10),
internalCAError (11),
tryLater (12),
authDataFail (13)
}
The values of CMCFailInfo have the following meanings:
badAlg indicates unrecognized or unsupported algorithm.
badMessageCheck indicates integrity check failed.
badRequest indicates transaction was not permitted or supported.
badTime indicates message time field was not sufficiently close to
the system time.
badCertId indicates no certificate could be identified matching the
provided criteria.
unsupportedExt indicates a requested X.509 extension is not
supported by the recipient CA.
mustArchiveKeys indicates private key material must be supplied.
badIdentity indicates identification control failed to verify.
Schaad & Myers Standards Track [Page 32]RFC 5272 CMC: Structures June 2008
popRequired indicates server requires a POP proof before issuing
certificate.
popFailed indicates POP processing failed.
noKeyReuse indicates server policy does not allow key reuse.
internalCAError indicates that the CA had an unknown internal
failure.
tryLater indicates that the server is not accepting requests at this
time and the client should try at a later time.
authDataFail indicates failure occurred during processing of
authenticated data.
If additional failure reasons are needed, they SHOULD use the
ExtendedFailureInfo item in the Extended CMC Status Info control.
However, for closed environments they can be defined using this type.
Such codes MUST be in the range from 1000 to 1999.
6.2. Identification and Identity Proof Controls
Some CAs and RAs require that a proof-of-identity be included in a
certification request. Many different ways of doing this exist with
different degrees of security and reliability. Most are familiar
with a bank's request to provide your mother's maiden name as a form
of identity proof. The reasoning behind requiring a proof-of-
identity can be found in Appendix C of [CRMF].
CMC provides a method to prove the client's identity based on a
client/server shared-secret. If clients support the Full PKI
Request, clients MUST implement this method of identity proof
(Section 6.2.2). Servers MUST provide this method, but MAY
additionally support bilateral methods of similar strength.
This document also provides an Identification control
(Section 6.2.3). This control is a simple method to allow a client
to state who they are to the server. Generally, a shared-secret AND
an identifier of that shared-secret are passed from the server to the
client. The identifier is placed in the Identification control, and
the shared-secret is used to compute the Identity Proof control.
6.2.1. Identity Proof Version 2 Control
The Identity Proof Version 2 control is identified by the OID:
id-cmc-identityProofV2 ::= { id-cmc 34 }
Schaad & Myers Standards Track [Page 33]RFC 5272 CMC: Structures June 2008
The Identity Proof Version 2 control has the ASN.1 definition:
IdentifyProofV2 ::= SEQUENCE {
hashAlgID AlgorithmIdentifier,
macAlgID AlgorithmIdentifier,
witness OCTET STRING
}
The fields of IdentityProofV2 have the following meaning:
hashAlgID is the identifier and parameters for the hash algorithm
used to convert the shared-secret into a key for the MAC
algorithm.
macAlgID is the identifier and the parameters for the message
authentication code algorithm used to compute the value of the
witness field.
witness is the identity proof.
The required method starts with an out-of-band transfer of a token
(the shared-secret). The shared-secret should be generated in a
random manner. The distribution of this token is beyond the scope of
this document. The client then uses this token for an identity proof
as follows:
1. The PKIData reqSequence field (encoded exactly as it appears in
the Full PKI Request including the sequence type and length) is
the value to be validated.
2. A hash of the shared-secret as a UTF8 string is computed using
hashAlgID.
3. A MAC is then computed using the value produced in Step 1 as the
message and the value from Step 2 as the key.
4. The result from Step 3 is then encoded as the witness value in
the Identity Proof Version 2 control.
When the server verifies the Identity Proof Version 2 control, it
computes the MAC value in the same way and compares it to the witness
value contained in the PKI Request.
If a server fails the verification of an Identity Proof Version 2
control, the CMCFailInfo value MUST be present in the Full PKI
Response and MUST have a value of badIdentity.
Schaad & Myers Standards Track [Page 34]RFC 5272 CMC: Structures June 2008
Reuse of the shared-secret on certification request retries allows
the client and server to maintain the same view of acceptable
identity proof values. However, reuse of the shared-secret can
potentially open the door for some types of attacks.
Implementations MUST be able to support tokens at least 16 characters
long. Guidance on the amount of entropy actually obtained from a
given length token based on character sets can be found in Appendix A
of [PASSWORD].
6.2.2. Identity Proof Control
The Identity Proof control is identified by the OID:
id-cmc-identityProof ::= { id-cmc 3 }
The Identity Proof control has the ASN.1 definition:
IdentifyProof ::= OCTET STRING
This control is processed in the same way as the Identity Proof
Version 2 control. In this case, the hash algorithm is fixed to
SHA-1 and the MAC algorithm is fixed to HMAC-SHA1.
6.2.3. Identification Control
Optionally, servers MAY require the inclusion of the unprotected
Identification control with an Identification Proof control. The
Identification control is intended to contain a text string that
assists the server in locating the shared-secret needed to validate
the contents of the Identity Proof control. If the Identification
control is included in the Full PKI Request, the derivation of the
key in Step 2 (from Section 6.2.1) is altered so that the hash of the
concatenation of the shared-secret and the UTF8 identity value
(without the type and length bytes) are hashed rather than just the
shared-secret.
The Identification control is identified by the OID:
id-cmc-identification ::= { id-cmc 2 }
The Identification control has the ASN.1 definition:
Identification ::= UTF8String
Schaad & Myers Standards Track [Page 35]RFC 5272 CMC: Structures June 2008
6.2.4. Hardware Shared-Secret Token Generation
The shared-secret between the EE and the server is sometimes computed
using a hardware device that generates a series of tokens. The EE
can therefore prove its identity by transferring this token in plain
text along with a name string. The above protocol can be used with a
hardware shared-secret token generation device by the following
modifications:
1. The Identification control MUST be included and MUST contain the
hardware-generated token.
2. The shared-secret value used above is the same hardware-generated
token.
3. All certification requests MUST have a subject name, and the
subject name MUST contain the fields required to identify the
holder of the hardware token device.
4. The entire certification request MUST be shrouded in some fashion
to prevent eavesdropping. Although the token is time critical,
an active eavesdropper cannot be permitted to extract the token
and submit a different certification request with the same token
value.
6.3. Linking Identity and POP Information
In a Full PKI Request, identity information about the client is
carried in the signature of the SignedData containing all of the
certification requests. Proof-of-possession information for key
pairs, however, is carried separately for each PKCS #10 or CRMF
certification request. (For keys capable of generating a digital
signature, the POP is provided by the signature on the PKCS #10 or
CRMF request. For encryption-only keys, the controls described in
Section 6.7 are used.) In order to prevent substitution-style
attacks, the protocol must guarantee that the same entity generated
both the POP and proof-of-identity information.
This section describes two mechanisms for linking identity and POP
information: witness values cryptographically derived from the
shared-secret (Section 6.3.1.3) and shared-secret/subject
distinguished name (DN) matching (Section 6.3.2). Clients and
servers MUST support the witness value technique. Clients and
servers MAY support shared-secret/subject DN matching or other
bilateral techniques of similar strength. The idea behind both
mechanisms is to force the client to sign some data into each
certification request that can be directly associated with the
Schaad & Myers Standards Track [Page 36]RFC 5272 CMC: Structures June 2008
shared-secret; this will defeat attempts to include certification
requests from different entities in a single Full PKI Request.
6.3.1. Cryptographic Linkage
The first technique that links identity and POP information forces
the client to include a piece of information cryptographically
derived from the shared-secret as a signed extension within each
certification request (PKCS #10 or CRMF).
6.3.1.1. POP Link Witness Version 2 Controls
The POP Link Witness Version 2 control is identified by the OID:
id-cmc-popLinkWitnessV2 ::= { id-cmc 33 }
The POP Link Witness Version 2 control has the ASN.1 definition:
PopLinkWitnessV2 ::= SEQUENCE {
keyGenAlgorithm AlgorithmIdentifier,
macAlgorithm AlgorithmIdentifier,
witness OCTET STRING
}
The fields of PopLinkWitnessV2 have the following meanings:
keyGenAlgorithm contains the algorithm used to generate the key for
the MAC algorithm. This will generally be a hash algorithm, but
could be a more complex algorithm.
macAlgorithm contains the algorithm used to create the witness
value.
witness contains the computed witness value.
This technique is useful if null subject DNs are used (because, for
example, the server can generate the subject DN for the certificate
based only on the shared-secret). Processing begins when the client
receives the shared-secret out-of-band from the server. The client
then computes the following values:
1. The client generates a random byte-string, R, which SHOULD be at
least 512 bits in length.
2. The key is computed from the shared-secret using the algorithm in
keyGenAlgorithm.
Schaad & Myers Standards Track [Page 37]RFC 5272 CMC: Structures June 2008
3. A MAC is then computed over the random value produced in Step 1,
using the key computed in Step 2.
4. The random value produced in Step 1 is encoded as the value of a
POP Link Random control. This control MUST be included in the
Full PKI Request.
5. The MAC value produced in Step 3 is placed in either the POP Link
Witness control or the witness field of the POP Link Witness V2
control.
* For CRMF, the POP Link Witness/POP Link Witness V2 control is
included in the controls field of the CertRequest structure.
* For PKCS #10, the POP Link Witness/POP Link Witness V2 control
is included in the attributes field of the
CertificationRequestInfo structure.
Upon receipt, servers MUST verify that each certification request
contains a copy of the POP Link Witness/POP Link Witness V2 control
and that its value was derived using the above method from the
shared-secret and the random string included in the POP Link Random
control.
The Identification control (see Section 6.2.3) or the subject DN of a
certification request can be used to help identify which shared-
secret was used.
6.3.1.2. POP Link Witness Control
The POP Link Witness control is identified by the OID:
id-cmc-popLinkWitness ::= { id-cmc 23 }
The POP Link Witness control has the ASN.1 definition:
PopLinkWitness ::= OCTET STRING
For this control, SHA-1 is used as the key generation algorithm.
HMAC-SHA1 is used as the mac algorithm.
6.3.1.3. POP Link Random Control
The POP Link Random control is identified by the OID:
id-cmc-popLinkRandom ::= { id-cmc 22 }
Schaad & Myers Standards Track [Page 38]RFC 5272 CMC: Structures June 2008
The POP Link Random control has the ASN.1 definition:
PopLinkRandom ::= OCTET STRING
6.3.2. Shared-Secret/Subject DN Linking
The second technique to link identity and POP information is to link
a particular subject distinguished name (subject DN) to the shared-
secrets that are distributed out-of-band and to require that clients
using the shared-secret to prove identity include that exact subject
DN in every certification request. It is expected that many client-
server connections that use shared-secret-based proof-of-identity
will use this mechanism. (It is common not to omit the subject DN
information from the certification request.)
When the shared-secret is generated and transferred out-of-band to
initiate the registration process (Section 6.2), a particular subject
DN is also associated with the shared-secret and communicated to the
client. (The subject DN generated MUST be unique per entity in
accordance with the CA policy; a null subject DN cannot be used. A
common practice could be to place the identification value as part of
the subject DN.) When the client generates the Full PKI Request, it
MUST use these two pieces of information as follows:
1. The client MUST include the specific subject DN that it received
along with the shared-secret as the subject name in every
certification request (PKCS #10 and/or CRMF) in the Full PKI
Request. The subject names in the certification requests MUST
NOT be null.
2. The client MUST include an Identity Proof control (Section 6.2.2)
or Identity Proof Version 2 control (Section 6.2.1), derived from
the shared-secret, in the Full PKI Request.
The server receiving this message MUST (a) validate the Identity
Proof control and then, (b) check that the subject DN included in
each certification request matches that associated with the shared-
secret. If either of these checks fails, the certification request
MUST be rejected.
6.3.3. Renewal and Rekey Messages
When doing a renewal or rekey certification request, linking identity
and POP information is simple. The client copies the subject DN for
a current signing certificate into the subject name field of each
certification request that is made. The POP for each certification
request will now cover that information. The outermost signature
layer is created using the current signing certificate, which allows
Schaad & Myers Standards Track [Page 39]RFC 5272 CMC: Structures June 2008
the original identity to be associated with the certification
request. Since the name in the current signing certificate and the
names in the certification requests match, the necessary linking has
been achieved.
6.4. Data Return Control
The Data Return control allows clients to send arbitrary data
(usually some type of internal state information) to the server and
to have the data returned as part of the Full PKI Response. Data
placed in a Data Return control is considered to be opaque to the
server. The same control is used for both Full PKI Requests and
Responses. If the Data Return control appears in a Full PKI Request,
the server MUST return it as part of the PKI Response.
In the event that the information in the Data Return control needs to
be confidential, it is expected that the client would apply some type
of encryption to the contained data, but the details of this are
outside the scope of this specification.
The Data Return control is identified by the OID:
id-cmc-dataReturn ::= { id-cmc 4 }
The Data Return control has the ASN.1 definition:
DataReturn ::= OCTET STRING
A client could use this control to place an identifier marking the
exact source of the private key material. This might be the
identifier of a hardware device containing the private key.
6.5. RA Certificate Modification Controls
These controls exist for RAs to be able to modify the contents of a
certification request. Modifications might be necessary for various
reasons. These include addition of certificate extensions or
modification of subject and/or subject alternative names.
Two controls exist for this purpose. The first control, Modify
Certification Request (Section 6.5.1), allows the RA to replace or
remove any field in the certificate. The second control, Add
Extensions (Section 6.5.2), only allows for the addition of
extensions.
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6.5.1. Modify Certification Request Control
The Modify Certification Request control is used by RAs to change
fields in a requested certificate.
The Modify Certification Request control is identified by the OID:
id-cmc-modCertTemplate ::= { id-cmc 31 }
The Modify Certification Request has the ASN.1 definition:
ModCertTemplate ::= SEQUENCE {
pkiDataReference BodyPartPath,
certReferences BodyPartList,
replace BOOLEAN DEFAULT TRUE,
certTemplate CertTemplate
}
The fields in ModCertTemplate have the following meaning:
pkiDataReference is the path to the PKI Request containing
certification request(s) to be modified.
certReferences refers to one or more certification requests in the
PKI Request referenced by pkiDataReference to be modified. Each
BodyPartID of the certReferences sequence MUST be equal to either
the bodyPartID of a TaggedCertificationRequest (PKCS #10) or the
certReqId of the CertRequest within a CertReqMsg (CRMF). By
definition, the certificate extensions included in the
certTemplate field are applied to every certification request
referenced in the certReferences sequence. If a request
corresponding to bodyPartID cannot be found, the CMCFailInfo with
a value of badRequest is returned that references this control.
replace specifies if the target certification request is to be
modified by replacing or deleting fields. If the value is TRUE,
the data in this control replaces the data in the target
certification request. If the value is FALSE, the data in the
target certification request is deleted. The action is slightly
different for the extensions field of certTemplate; each extension
is treated individually rather than as a single unit.
certTemplate is a certificate template object [CRMF]. If a field is
present and replace is TRUE, it replaces that field in the
certification request. If the field is present and replace is
FALSE, the field in the certification request is removed. If the
field is absent, no action is performed. Each extension is
treated as a single field.
Schaad & Myers Standards Track [Page 41]RFC 5272 CMC: Structures June 2008
Servers MUST be able to process all extensions defined, but not
prohibited, in [PKIXCERT]. Servers are not required to be able to
process every X.509v3 extension transmitted using this protocol, nor
are they required to be able to process other, private extensions.
Servers are not required to put all RA-requested extensions into a
certificate. Servers are permitted to modify RA-requested
extensions. Servers MUST NOT alter an extension so as to reverse the
meaning of a client-requested extension. If a certification request
is denied due to the inability to handle a requested extension and a
Full PKI Response is returned, the server MUST return a CMCFailInfo
value with the value of unsupportedExt.
If a certification request is the target of multiple Modify
Certification Request controls, the behavior is:
o If control A exists in a layer that contains the layer of control
B, control A MUST override control B. In other words, controls
should be applied from the innermost layer to the outermost layer.
o If control A and control B are in the same PKIData (i.e., the same
wrapping layer), the order of application is non-determinate.
The same order of application is used if a certification request is
the target of both a Modify Certification Request control and an Add
Extensions control.
6.5.2. Add Extensions Control
The Add Extensions control has been deprecated in favor of the Modify
Certification Request control. It was replaced so that fields in the
certification request other than extensions could be modified.
The Add Extensions control is used by RAs to specify additional
extensions that are to be included in certificates.
The Add Extensions control is identified by the OID:
id-cmc-addExtensions ::= { id-cmc 8 }
The Add Extensions control has the ASN.1 definition:
AddExtensions ::= SEQUENCE {
pkiDataReference BodyPartID,
certReferences SEQUENCE OF BodyPartID,
extensions SEQUENCE OF Extension
}
Schaad & Myers Standards Track [Page 42]RFC 5272 CMC: Structures June 2008
The fields in AddExtensions have the following meaning:
pkiDataReference contains the body part identity of the embedded
certification request.
certReferences is a list of references to one or more of the
certification requests contained within a PKIData. Each body part
identifier of the certReferences sequence MUST be equal to either
the bodyPartID of a TaggedCertificationRequest (PKCS #10) or the
certReqId of the CertRequest within a CertReqMsg (CRMF). By
definition, the listed extensions are to be applied to every
certification request referenced in the certReferences sequence.
If a certification request corresponding to bodyPartID cannot be
found, the CMCFailInfo with a value of badRequest is returned
referencing this control.
extensions is a sequence of extensions to be applied to the
referenced certification requests.
Servers MUST be able to process all extensions defined, but not
prohibited, in [PKIXCERT]. Servers are not required to be able to
process every X.509v3 extension transmitted using this protocol, nor
are they required to be able to process other, private extensions.
Servers are not required to put all RA-requested extensions into a
certificate. Servers are permitted to modify RA-requested
extensions. Servers MUST NOT alter an extension so as to reverse the
meaning of a client-requested extension. If a certification request
is denied due to the inability to handle a requested extension and a
response is returned, the server MUST return a CMCFailInfo with the
value of unsupportedExt.
If multiple Add Extensions controls exist in a Full PKI Request, the
exact behavior is left up to the CA policy. However, it is
recommended that the following policy be used. These rules would be
applied to individual extensions within an Add Extensions control (as
opposed to an "all or nothing" approach).
1. If the conflict is within a single PKIData, the certification
request would be rejected with a CMCFailInfo value of badRequest.
2. If the conflict is between different PKIData, the outermost
version of the extension would be used (allowing an RA to
override the requested extension).
Schaad & Myers Standards Track [Page 43]RFC 5272 CMC: Structures June 2008
6.6. Transaction Identifier Control and Sender and Recipient Nonce
Controls
Transactions are identified and tracked with a transaction
identifier. If used, clients generate transaction identifiers and
retain their value until the server responds with a Full PKI Response
that completes the transaction. Servers correspondingly include
received transaction identifiers in the Full PKI Response.
The Transaction Identifier control is identified by the OID:
id-cmc-transactionId ::= { id-cmc 5 }
The Transaction Identifier control has the ASN.1 definition:
TransactionId ::= INTEGER
The Transaction Identifier control identifies a given transaction.
It is used by client and server to manage the state of an operation.
Clients MAY include a Transaction Identifier control in a request.
If the original request contains a Transaction Identifier control,
all subsequent requests and responses MUST include the same
Transaction Identifier control.
Replay protection is supported through the use of the Sender and
Recipient Nonce controls. If nonces are used, in the first message
of a transaction, a Recipient Nonce control is not transmitted; a
Sender Nonce control is included by the transaction originator and
retained for later reference. The recipient of a Sender Nonce
control reflects this value back to the originator as a Recipient
Nonce control and includes its own Sender Nonce control. Upon
receipt by the transaction originator of this response, the
transaction originator compares the value of Recipient Nonce control
to its retained value. If the values match, the message can be
accepted for further security processing. The received value for a
Sender Nonce control is also retained for inclusion in the next
message associated with the same transaction.
The Sender Nonce and Recipient Nonce controls are identified by the
OIDs:
id-cmc-senderNonce ::= { id-cmc 6 }
id-cmc-recipientNonce ::= { id-cmc 7 }
The Sender Nonce control has the ASN.1 definition:
SenderNonce ::= OCTET STRING
Schaad & Myers Standards Track [Page 44]RFC 5272 CMC: Structures June 2008
The Recipient Nonce control has the ASN.1 definition:
RecipientNonce ::= OCTET STRING
Clients MAY include a Sender Nonce control in the initial PKI
Request. If a message includes a Sender Nonce control, the response
MUST include the transmitted value of the previously received Sender
Nonce control as a Recipient Nonce control and include a new value as
its Sender Nonce control.
6.7. Encrypted and Decrypted POP Controls
Servers MAY require that this POP method be used only if another POP
method is unavailable. Servers SHOULD reject all certification
requests contained within a PKIData if any required POP is missing
for any element within the PKIData.
Many servers require proof that the entity that generated the
certification request actually possesses the corresponding private
component of the key pair. For keys that can be used as signature
keys, signing the certification request with the private key serves
as a POP on that key pair. With keys that can only be used for
encryption operations, POP MUST be performed by forcing the client to
decrypt a value. See Section 5 of [CRMF] for a detailed discussion
of POP.
By necessity, POP for encryption-only keys cannot be done in one
round-trip, since there are four distinct steps:
1. Client tells the server about the public component of a new
encryption key pair.
2. Server sends the client a POP challenge, encrypted with the
presented public encryption key.
3. Client decrypts the POP challenge using the private key that
corresponds to the presented public key and sends the plaintext
back to the server.
4. Server validates the decrypted POP challenge and continues
processing the certification request.
CMC defines two different controls. The first deals with the
encrypted challenge sent from the server to the user in Step 2. The
second deals with the decrypted challenge sent from the client to the
server in Step 3.
Schaad & Myers Standards Track [Page 45]RFC 5272 CMC: Structures June 2008
The Encrypted POP control is used to send the encrypted challenge
from the server to the client as part of the PKIResponse. (Note that
it is assumed that the message sent in Step 1 above is a Full PKI
Request and that the response in Step 2 is a Full PKI Response
including a CMCFailInfo specifying that a POP is explicitly required,
and providing the POP challenge in the encryptedPOP control.)
The Encrypted POP control is identified by the OID:
id-cmc-encryptedPOP ::= { id-cmc 9 }
The Encrypted POP control has the ASN.1 definition:
EncryptedPOP ::= SEQUENCE {
request TaggedRequest,
cms ContentInfo,
thePOPAlgID AlgorithmIdentifier,
witnessAlgID AlgorithmIdentifier,
witness OCTET STRING
}
The Decrypted POP control is identified by the OID:
id-cmc-decryptedPOP ::= { id-cmc 10 }
The Decrypted POP control has the ASN.1 definition:
DecryptedPOP ::= SEQUENCE {
bodyPartID BodyPartID,
thePOPAlgID AlgorithmIdentifier,
thePOP OCTET STRING
}
The encrypted POP algorithm works as follows:
1. The server randomly generates the POP Proof Value and associates
it with the request.
2. The server returns the Encrypted POP control with the following
fields set:
request is the original certification request (it is included
here so the client need not keep a copy of the request).
cms is an EnvelopedData, the encapsulated content type being id-
data and the content being the POP Proof Value; this value
needs to be long enough that one cannot reverse the value from
the witness hash. If the certification request contains a
Schaad & Myers Standards Track [Page 46]RFC 5272 CMC: Structures June 2008
Subject Key Identifier (SKI) extension, then the recipient
identifier SHOULD be the SKI. If the issuerAndSerialNumber
form is used, the IssuerName MUST be encoded as NULL and the
SerialNumber as the bodyPartID of the certification request.
thePOPAlgID identifies the algorithm to be used in computing the
return POP value.
witnessAlgID identifies the hash algorithm used on the POP Proof
Value to create the field witness.
witness is the hashed value of the POP Proof Value.
3. The client decrypts the cms field to obtain the POP Proof Value.
The client computes H(POP Proof Value) using the witnessAlgID and
compares to the value of witness. If the values do not compare
or the decryption is not successful, the client MUST abort the
enrollment process. The client aborts the process by sending a
request containing a CMC Status Info control with CMCFailInfo
value of popFailed.
4. The client creates the Decrypted POP control as part of a new
PKIData. The fields in the DecryptedPOP are:
bodyPartID refers to the certification request in the new PKI
Request.
thePOPAlgID is copied from the encryptedPOP.
thePOP contains the possession proof. This value is computed by
thePOPAlgID using the POP Proof Value and the request.
5. The server then re-computes the value of thePOP from its cached
value and the request and compares to the value of thePOP. If
the values do not match, the server MUST NOT issue the
certificate. The server MAY re-issue a new challenge or MAY fail
the request altogether.
When defining the algorithms for thePOPAlgID and witnessAlgID, care
must be taken to ensure that the result of witnessAlgID is not a
useful value to shortcut the computation with thePOPAlgID. The POP
Proof Value is used as the secret value in the HMAC algorithm and the
request is used as the data. If the POP Proof Value is greater than
64 bytes, only the first 64 bytes of the POP Proof Value is used as
the secret.
Schaad & Myers Standards Track [Page 47]RFC 5272 CMC: Structures June 2008
One potential problem with the algorithm above is the amount of state
that a CA needs to keep in order to verify the returned POP value.
The following describes one of many possible ways of addressing the
problem by reducing the amount of state kept on the CA to a single
(or small set) of values.
1. Server generates random seed x, constant across all requests.
(The value of x would normally be altered on a regular basis and
kept for a short time afterwards.)
2. For certification request R, server computes y = F(x,R). F can
be, for example, HMAC-SHA1(x,R). All that's important for
statelessness is that y be consistently computable with only
known state constant x and function F, other inputs coming from
the certification request structure. y should not be predictable
based on knowledge of R, thus the use of a one-way function like
HMAC-SHA1.
6.8. RA POP Witness Control
In a certification request scenario that involves an RA, the CA may
allow (or require) that the RA perform the POP protocol with the
entity that generated the certification request. In this case, the
RA needs a way to inform the CA that it has done the POP. The RA POP
Witness control addresses this issue.
The RA POP Witness control is identified by the OID:
id-cmc-lraPOPWitness ::= { id-cmc 11 }
The RA POP Witness control has the ASN.1 definition:
LraPopWitness ::= SEQUENCE {
pkiDataBodyid BodyPartID,
bodyIds SEQUENCE of BodyPartID
}
The fields in LraPOPWitness have the following meaning:
pkiDataBodyid contains the body part identifier of the nested
TaggedContentInfo containing the client's Full PKI Request.
pkiDataBodyid is set to 0 if the request is in the current
PKIData.
bodyIds is a list of certification requests for which the RA has
performed an out-of-band authentication. The method of
authentication could be archival of private key material,
challenge-response, or other means.
Schaad & Myers Standards Track [Page 48]RFC 5272 CMC: Structures June 2008
If a certification server does not allow an RA to do the POP
verification, it returns a CMCFailInfo with the value of popFailed.
The CA MUST NOT start a challenge-response to re-verify the POP
itself.
6.9. Get Certificate Control
Everything described in this section is optional to implement.
The Get Certificate control is used to retrieve a previously issued
certificate from a certificate repository. A CA, an RA, or an
independent service may provide this repository. The clients
expected to use this facility are those where a fully deployed
directory is either infeasible or undesirable.
The Get Certificate control is identified by the OID:
id-cmc-getCert ::= { id-cmc 15 }
The Get Certificate control has the ASN.1 definition:
GetCert ::= SEQUENCE {
issuerName GeneralName,
serialNumber INTEGER }
The fields in GetCert have the following meaning:
issuerName is the name of the certificate issuer.
serialNumber identifies the certificate to be retrieved.
The server that responds to this request places the requested
certificate in the certificates field of a SignedData. If the Get
Certificate control is the only control in a Full PKI Request, the
response should be a Simple PKI Response.
6.10. Get CRL Control
Everything described in this section is optional to implement.
The Get CRL control is used to retrieve CRLs from a repository of
CRLs. A CA, an RA, or an independent service may provide this
repository. The clients expected to use this facility are those
where a fully deployed directory is either infeasible or undesirable.
The Get CRL control is identified by the OID:
id-cmc-getCRL ::= { id-cmc 16 }
Schaad & Myers Standards Track [Page 49]RFC 5272 CMC: Structures June 2008
The Get CRL control has the ASN.1 definition:
GetCRL ::= SEQUENCE {
issuerName Name,
cRLName GeneralName OPTIONAL,
time GeneralizedTime OPTIONAL,
reasons ReasonFlags OPTIONAL }
The fields in a GetCRL have the following meanings:
issuerName is the name of the CRL issuer.
cRLName may be the value of CRLDistributionPoints in the subject
certificate or equivalent value in the event the certificate does
not contain such a value.
time is used by the client to specify from among potentially several
issues of CRL that one whose thisUpdate value is less than but
nearest to the specified time. In the absence of a time
component, the CA always returns with the most recent CRL.
reasons is used to specify from among CRLs partitioned by revocation
reason. Implementers should bear in mind that while a specific
revocation request has a single CRLReason code -- and consequently
entries in the CRL would have a single CRLReason code value -- a
single CRL can aggregate information for one or more reasonFlags.
A server responding to this request places the requested CRL in the
crls field of a SignedData. If the Get CRL control is the only
control in a Full PKI Request, the response should be a Simple PKI
Response.
6.11. Revocation Request Control
The Revocation Request control is used to request that a certificate
be revoked.
The Revocation Request control is identified by the OID:
id-cmc-revokeRequest ::= { id-cmc 17 }
Schaad & Myers Standards Track [Page 50]RFC 5272 CMC: Structures June 2008
The Revocation Request control has the ASN.1 definition:
RevokeRequest ::= SEQUENCE {
issuerName Name,
serialNumber INTEGER,
reason CRLReason,
invalidityDate GeneralizedTime OPTIONAL,
sharedSecret OCTET STRING OPTIONAL,
comment UTF8string OPTIONAL }
The fields of RevokeRequest have the following meaning:
issuerName is the issuerName of the certificate to be revoked.
serialNumber is the serial number of the certificate to be revoked.
reason is the suggested CRLReason code for why the certificate is
being revoked. The CA can use this value at its discretion in
building the CRL.
invalidityDate is the suggested value for the Invalidity Date CRL
Extension. The CA can use this value at its discretion in
building the CRL.
sharedSecret is a secret value registered by the EE when the
certificate was obtained to allow for revocation of a certificate
in the event of key loss.
comment is a human-readable comment.
For a revocation request to be reliable in the event of a dispute, a
strong proof-of-origin is required. However, in the instance when an
EE has lost use of its signature private key, it is impossible for
the EE to produce a digital signature (prior to the certification of
a new signature key pair). The Revoke Request control allows the EE
to send the CA a shared-secret that may be used as an alternative
authenticator in the instance of loss of use of the EE's signature
private key. The acceptability of this practice is a matter of local
security policy.
It is possible to sign the revocation for the lost certificate with a
different certificate in some circumstances. A client can sign a
revocation for an encryption key with a signing certificate if the
name information matches. Similarly, an administrator or RA can be
assigned the ability to revoke the certificate of a third party.
Acceptance of the revocation by the server depends on local policy in
these cases.
Schaad & Myers Standards Track [Page 51]RFC 5272 CMC: Structures June 2008
Clients MUST provide the capability to produce a digitally signed
Revocation Request control. Clients SHOULD be capable of producing
an unsigned Revocation Request control containing the EE shared-
secret (the unsigned message consisting of a SignedData with no
signatures). If a client provides shared-secret-based self-
revocation, the client MUST be capable of producing a Revocation
Request control containing the shared-secret. Servers MUST be
capable of accepting both forms of revocation requests.
The structure of an unsigned, shared-secret-based revocation request
is a matter of local implementation. The shared-secret does not need
to be encrypted when sent in a Revocation Request control. The
shared-secret has a one-time use (i.e., it is used to request
revocation of the certificate), and public knowledge of the shared-
secret after the certificate has been revoked is not a problem.
Clients need to inform users that the same shared-secret SHOULD NOT
be used for multiple certificates.
A Full PKI Response MUST be returned for a revocation request.
6.12. Registration and Response Information Controls
The Registration Information control allows for clients to pass
additional information as part of a Full PKI Request.
The Registration Information control is identified by the OID:
id-cmc-regInfo ::= { id-cmc 18 }
The Registration Information control has the ASN.1 definition:
RegInfo ::= OCTET STRING
The content of this data is based on bilateral agreement between the
client and server.
The Response Information control allows a server to return additional
information as part of a Full PKI Response.
The Response Information control is identified by the OID:
id-cmc-responseInfo ::= { id-cmc 19 }
The Response Information control has the ASN.1 definition:
ResponseInfo ::= OCTET STRING
Schaad & Myers Standards Track [Page 52]RFC 5272 CMC: Structures June 2008
The content of this data is based on bilateral agreement between the
client and server.
6.13. Query Pending Control
In some environments, process requirements for manual intervention or
other identity checks can delay the return of the certificate. The
Query Pending control allows clients to query a server about the
state of a pending certification request. The server returns a
pendToken as part of the Extended CMC Status Info and the CMC Status
Info controls (in the otherInfo field). The client copies the
pendToken into the Query Pending control to identify the correct
certification request to the server. The server returns a suggested
time for the client to query for the state of a pending certification
request.
The Query Pending control is identified by the OID:
id-cmc-queryPending ::= { id-cmc 21 }
The Query Pending control has the ASN.1 definition:
QueryPending ::= OCTET STRING
If a server returns a pending or partial CMCStatusInfo (the
transaction is still pending), the otherInfo MAY be omitted. If the
otherInfo is not omitted, the value of 'pendInfo' MUST be the same as
the original pendInfo value.
6.14. Confirm Certificate Acceptance Control
Some CAs require that clients give a positive confirmation that the
certificates issued to the EE are acceptable. The Confirm
Certificate Acceptance control is used for that purpose. If the CMC
Status Info on a PKI Response is confirmRequired, then the client
MUST return a Confirm Certificate Acceptance control contained in a
Full PKI Request.
Clients SHOULD wait for the PKI Response from the server that the
confirmation has been received before using the certificate for any
purpose.
The Confirm Certificate Acceptance control is identified by the OID:
id-cmc-confirmCertAcceptance ::= { id-cmc 24 }
Schaad & Myers Standards Track [Page 53]RFC 5272 CMC: Structures June 2008
The Confirm Certificate Acceptance control has the ASN.1 definition:
CMCCertId ::= IssuerAndSerialNumber
CMCCertId contains the issuer and serial number of the certificate
being accepted.
Servers MUST return a Full PKI Response for a Confirm Certificate
Acceptance control.
Note that if the CA includes this control, there will be two full
round-trips of messages.
1. The client sends the certification request to the CA.
2. The CA returns a Full PKI Response with the certificate and this
control.
3. The client sends a Full PKI Request to the CA with an Extended
CMC Status Info control accepting and a Confirm Certificate
Acceptance control or an Extended CMC Status Info control
rejecting the certificate.
4. The CA sends a Full PKI Response to the client with an Extended
CMC Status Info of success.
6.15. Publish Trust Anchors Control
The Publish Trust Anchors control allows for the distribution of set
trust anchors from a central authority to an EE. The same control is
also used to update the set of trust anchors. Trust anchors are
distributed in the form of certificates. These are expected, but not
required, to be self-signed certificates. Information is extracted
from these certificates to set the inputs to the certificates
validation algorithm in Section 6.1.1 of [PKIXCERT].
The Publish Trust Anchors control is identified by the OID:
id-cmc-trustedAnchors ::= { id-cmc 26 }
The Publish Trust Anchors control has the ASN.1 definition:
PublishTrustAnchors ::= SEQUENCE {
seqNumber INTEGER,
hashAlgorithm AlgorithmIdentifier,
anchorHashes SEQUENCE OF OCTET STRING
}
Schaad & Myers Standards Track [Page 54]RFC 5272 CMC: Structures June 2008
The fields in PublishTrustAnchors have the following meaning:
seqNumber is an integer indicating the location within a sequence of
updates.
hashAlgorithm is the identifier and parameters for the hash
algorithm that is used in computing the values of the anchorHashes
field. All implementations MUST implement SHA-1 for this field.
anchorHashes are the hashes for the certificates that are to be
treated as trust anchors by the client. The actual certificates
are transported in the certificate bag of the containing
SignedData structure.
While it is recommended that the sender place the certificates that
are to be trusted in the PKI Response, it is not required as the
certificates should be obtainable using normal discovery techniques.
Prior to accepting the trust anchors changes, a client MUST at least
do the following: validate the signature on the PKI Response to a
current trusted anchor, check with policy to ensure that the signer
is permitted to use the control, validate that the authenticated
publish time in the signature is near to the current time, and
validate that the sequence number is greater than the previously used
one.
In the event that multiple agents publish a set of trust anchors, it
is up to local policy to determine how the different trust anchors
should be combined. Clients SHOULD be able to handle the update of
multiple trust anchors independently.
Note: Clients that handle this control must use extreme care in
validating that the operation is permissible. Incorrect handling of
this control allows for an attacker to change the set of trust
anchors on the client.
6.16. Authenticated Data Control
The Authenticated Data control allows a server to provide data back
to the client in an authenticated manner. This control uses the
Authenticated Data structure to allow for validation of the data.
This control is used where the client has a shared-secret and a
secret identifier with the server, but where a trust anchor has not
yet been downloaded onto the client so that a signing certificate for
the server cannot be validated. The specific case that this control
was created for use with is the Publish Trust Anchors control
(Section 6.15), but it may be used in other cases as well.
Schaad & Myers Standards Track [Page 55]RFC 5272 CMC: Structures June 2008
The Authenticated Data control is identified by the OID:
id-cmc-authData ::= { id-cmc 27 }
The Authenticated Data control has the ASN.1 definition:
AuthPublish ::= BodyPartID
AuthPublish is a body part identifier that refers to a member of the
cmsSequence element for the current PKI Response or PKI Data. The
cmsSequence element is AuthenticatedData. The encapsulated content
is an id-cct-PKIData. The controls in the controlSequence need to be
processed if the authentication succeeds. (One example is the
Publish Trust Anchors control in Section 6.15.)
If the authentication operation fails, the CMCFailInfo authDataFail
is returned.
6.17. Batch Request and Response Controls
These controls allow for an RA to collect multiple requests together
into a single Full PKI Request and forward it to a CA. The server
would then process the requests and return the results in a Full PKI
Response.
The Batch Request control is identified by the OID:
id-cmc-batchRequests ::= {id-cmc 28}
The Batch Response control is identified by the OID:
id-cmc-batchResponses ::= {id-cmc 29}
Both the Batch Request and Batch Response controls have the ASN.1
definition:
BodyPartList ::= SEQUENCE of BodyPartID
The data associated with these controls is a set of body part
identifiers. Each request/response is placed as an individual entry
in the cmcSequence of the new PKIData/PKIResponse. The body part
identifiers of these entries are then placed in the body part list
associated with the control.
When a server processes a Batch Request control, it MAY return the
responses in one or more PKI Responses. A CMCStatus value of partial
is returned on all but the last PKI Response. The CMCStatus would be
success if the Batch Requests control was processed; the responses
Schaad & Myers Standards Track [Page 56]RFC 5272 CMC: Structures June 2008
are created with their own CMCStatus code. Errors on individual
requests are not propagated up to the top level.
When a PKI Response with a CMCStatus value of partial is returned,
the Query Pending control (Section 6.13) is used to retrieve
additional results. The returned status includes a suggested time
after which the client should ask for the additional results.
6.18. Publication Information Control
The Publication Information control allows for modifying publication
of already issued certificates, both for publishing and removal from
publication. A common usage for this control is to remove an
existing certificate from publication during a rekey operation. This
control should always be processed after the issuance of new
certificates and revocation requests. This control should not be
processed if a certificate failed to be issued.
The Publication Information control is identified by the OID:
id-cmc-publishCert ::= { id-cmc 30 }
The Publication Information control has the ASN.1 definition:
CMCPublicationInfo ::= SEQUENCE {
hashAlg AlgorithmIdentifier,
certHashes SEQUENCE of OCTET STRING,
pubInfo PKIPublicationInfo
PKIPublicationInfo ::= SEQUENCE {
action INTEGER {
dontPublish (0),
pleasePublish (1) },
pubInfos SEQUENCE SIZE (1..MAX) OF SinglePubInfo OPTIONAL }
-- pubInfos MUST NOT be present if action is "dontPublish"
-- (if action is "pleasePublish" and pubInfos is omitted,
-- "dontCare" is assumed)
SinglePubInfo ::= SEQUENCE {
pubMethod INTEGER {
dontCare (0),
x500 (1),
web (2),
ldap (3) },
pubLocation GeneralName OPTIONAL }
}
Schaad & Myers Standards Track [Page 57]RFC 5272 CMC: Structures June 2008
The fields in CMCPublicationInfo have the following meaning:
hashAlg is the algorithm identifier of the hash algorithm used to
compute the values in certHashes.
certHashes are the hashes of the certificates for which publication
is to change.
pubInfo is the information where and how the certificates should be
published. The fields in pubInfo (taken from [CRMF]) have the
following meanings:
action indicates the action the service should take. It has two
values:
dontPublish indicates that the PKI should not publish the
certificate (this may indicate that the requester intends to
publish the certificate him/herself). dontPublish has the
added connotation of removing from publication the
certificate if it is already published.
pleasePublish indicates that the PKI MAY publish the
certificate using whatever means it chooses unless pubInfos
is present. Omission of the CMC Publication Info control
results in the same behavior.
pubInfos pubInfos indicates how (e.g., X500, Web, IP Address) the
PKI SHOULD publish the certificate.
A single certificate SHOULD NOT appear in more than one Publication
Information control. The behavior is undefined in the event that it
does.
6.19. Control Processed Control
The Control Processed control allows an RA to indicate to subsequent
control processors that a specific control has already been
processed. This permits an RA in the middle of a processing stream
to process a control defined either in a local context or in a
subsequent document.
The Control Processed control is identified by the OID:
id-cmc-controlProcessed ::= { id-cmc 32 }
Schaad & Myers Standards Track [Page 58]RFC 5272 CMC: Structures June 2008
The Control Processed control has the ASN.1 definition:
ControlList ::= SEQUENCE {
bodyList SEQUENCE SIZE (1..MAX) OF BodyPartReference
}
bodyList is a series of body part identifiers that form a path to
each of the controls that were processed by the RA. This control
is only needed for those controls that are not part of this
standard and thus would cause an error condition of a server
attempting to deal with a control not defined in this document.
No error status is needed since an error causes the RA to return
the request to the client with the error rather than passing the
request on to the next server in the processing list.
7. Registration Authorities
This specification permits the use of RAs. An RA sits between the EE
and the CA. From the EE's perspective, the RA appears to be the CA,
and from the server, the RA appears to be a client. RAs receive the
PKI Requests, perform local processing and then forward them onto
CAs. Some of the types of local processing that an RA can perform
include:
o Batching multiple PKI Requests together,
o Performing challenge/response POP proofs,
o Adding private or standardized certificate extensions to all
certification requests,
o Archiving private key material,
o Routing requests to different CAs.
When an RA receives a PKI Request, it has three options: it may
forward the PKI Request without modification, it may add a new
wrapping layer to the PKI Request, or it may remove one or more
existing layers and add a new wrapping layer.
When an RA adds a new wrapping layer to a PKI Request, it creates a
new PKIData. The new layer contains any controls required (for
example, if the RA does the POP proof for an encryption key or the
Add Extension control to modify a PKI Request) and the client PKI
Request. The client PKI Request is placed in the cmsSequence if it
is a Full PKI Request and in the reqSequence if it is a Simple PKI
Request. If an RA is batching multiple client PKI Requests together,
Schaad & Myers Standards Track [Page 59]RFC 5272 CMC: Structures June 2008
then each client PKI Request is placed into the appropriate location
in the RA's PKIData object along with all relevant controls.
If multiple RAs are in the path between the EE and the CA, this will
lead to multiple wrapping layers on the request.
In processing a PKI Request, an RA MUST NOT alter any certification
requests (PKCS #10 or CRMF) as any alteration would invalidate the
signature on the certification request and thus the POP for the
private key.
An example of how this would look is illustrated by the following
figure:
SignedData (by RA)
PKIData
controlSequence
RA added control statements
reqSequence
Zero or more Simple PKI Requests from clients
cmsSequence
Zero or more Full PKI Requests from clients
SignedData (signed by client)
PKIData
Under some circumstances, an RA is required to remove wrapping
layers. The following sections look at the processing required if
encryption layers and signing layers need to be removed.
7.1. Encryption Removal
There are two cases that require an RA to remove or change encryption
in a PKI Request. In the first case, the encryption was applied for
the purposes of protecting the entire PKI Request from unauthorized
entities. If the CA does not have a Recipient Info entry in the
encryption layer, the RA MUST remove the encryption layer. The RA
MAY add a new encryption layer with or without adding a new signing
layer.
The second change of encryption that may be required is to change the
encryption inside of a signing layer. In this case, the RA MUST
remove all signing layers containing the encryption. All control
statements MUST be merged according to local policy rules as each
signing layer is removed and the resulting merged controls MUST be
placed in a new signing layer provided by the RA. If the signing
layer provided by the EE needs to also be removed, the RA can also
remove this layer.
Schaad & Myers Standards Track [Page 60]RFC 5272 CMC: Structures June 2008
7.2. Signature Layer Removal
Only two instances exist where an RA should remove a signature layer
on a Full PKI Request: if an encryption layer needs to be modified
within the request, or if a CA will not accept secondary delegation
(i.e., multiple RA signatures). In all other situations, RAs SHOULD
NOT remove a signing layer from a PKI Request.
If an RA removes a signing layer from a PKI Request, all control
statements MUST be merged according to local policy rules. The
resulting merged control statements MUST be placed in a new signing
layer provided by the RA.
8. Security Considerations
Mechanisms for thwarting replay attacks may be required in particular
implementations of this protocol depending on the operational
environment. In cases where the CA maintains significant state
information, replay attacks may be detectable without the inclusion
of the optional nonce mechanisms. Implementers of this protocol need
to carefully consider environmental conditions before choosing
whether or not to implement the senderNonce and recipientNonce
controls described in Section 6.6. Developers of state-constrained
PKI clients are strongly encouraged to incorporate the use of these
controls.
Extreme care needs to be taken when archiving a signing key. The
holder of the archived key may have the ability to use the key to
generate forged signatures. There are however reasons why a signing
key should be archived. An archived CA signing key can be recovered
in the event of failure to continue to produced CRLs following a
disaster.
Due care must be taken prior to archiving keys. Once a key is given
to an archiving entity, the archiving entity could use the keys in a
way not conducive to the archiving entity. Users should be made
especially aware that proper verification is made of the certificate
used to encrypt the private key material.
Clients and servers need to do some checks on cryptographic
parameters prior to issuing certificates to make sure that weak
parameters are not used. A description of the small subgroup attack
is provided in [X942]. Methods of avoiding the small subgroup attack
can be found in [SMALL-GROUP]. CMC implementations ought to be aware
of this attack when doing parameter validations.
Schaad & Myers Standards Track [Page 61]
RFC 5272 CMC: Structures June 2008
When using a shared-secret for authentication purposes, the shared-
secret should be generated using good random number techniques
[RANDOM]. User selection of the secret allows for dictionary attacks
to be mounted.
Extreme care must be used when processing the Publish Trust Anchors
control. Incorrect processing can lead to the practice of slamming
where an attacker changes the set of trusted anchors in order to
weaken security.
One method of controlling the use of the Publish Trust Anchors
control is as follows. The client needs to associate with each trust
anchor accepted by the client the source of the trust anchor.
Additionally, the client should associate with each trust anchor the
types of messages for which the trust anchor is valid (i.e., is the
trust anchor used for validating S/MIME messages, TLS, or CMC
enrollment messages?).
When a new message is received with a Publish Trust Anchors control,
the client would accept the set of new trust anchors for specific
applications only if the signature validates, the signer of the
message has the required policy approval for updating the trust
anchors, and local policy also would allow updating the trust
anchors.
The CMS AuthenticatedData structure provides message integrity, it
does not provide message authentication in all cases. When using
MACs in this document the following restrictions need to be observed.
All messages should be for a single entity. If two entities are
placed in a single message, the entities can generate new messages
that have a valid MAC and might be assumed to be from the original
message sender. All entities that have access to the shared-secret
can generate messages that will have a successful MAC validation.
This means that care must be taken to keep this value secret.
Whenever possible, the SignedData structure should be used in
preference to the AuthenticatedData structure.
9. IANA Considerations
This document defines a number of control objects. These are
identified by Object Identifiers (OIDs). The objects are defined
from an arc delegated by IANA to the PKIX Working Group. No further
action by IANA is necessary for this document or any anticipated
updates.
Schaad & Myers Standards Track [Page 62]
RFC 5272 CMC: Structures June 2008
10. Acknowledgments
The authors and the PKIX Working Group are grateful for the
participation of Xiaoyi Liu and Jeff Weinstein in helping to author
the original versions of this document.
The authors would like to thank Brian LaMacchia for his work in
developing and writing up many of the concepts presented in this
document. The authors would also like to thank Alex Deacon and Barb
Fox for their contributions.
11. References
11.1. Normative References
[CMS] Housley, R., "Cryptographic Message Syntax (CMS)",
RFC 3852, July 2004.
[CRMF] Schaad, J., "Internet X.509 Certification Request
Message Format", RFC 4211, January 2005.
[DH-POP] Prafullchandra, H. and J. Schaad, "Diffie-Hellman
Proof-of-Possession Algorithms", RFC 2875, June 2000.
[PKCS10] Kaliski, B., "PKCS #10: Certification Request Syntax
v1.5", RFC 2314, October 1997.
Note that this version of PKCS #10 is used for
compatibility with the use of 1988 ASN.1 syntax. An
effort is currently underway in the PKIX working group
to update to use 2003 ASN.1 syntax.
[PKIXCERT] Housley, R., Ford, W., Polk, W., and D. Solo,
"Internet X.509 Public Key Infrastructure Certificate
and Certificate Revocation List (CRL) Profile",
RFC 3280, April 2002.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, BCP 14, March 1997.
11.2. Informative References
[CMC-TRANS] Schaad, J. and M. Myers, "Certificate Management over
CMS (CMC): Transport Protocols", RFC 5273, June 2008.
[CMC-COMPL] Schaad, J. and M. Myers, "Certificate Management
Messages over CMS (CMC): Compliance Requirements",
RFC 5274, June 2008.
Schaad & Myers Standards Track [Page 63]RFC 5272 CMC: Structures June 2008
[PASSWORD] Burr, W., Dodson, D., and W. Polk, "Electronic
Authentication Guideline", NIST SP 800-63, April 2006.
[RANDOM] Eastlake, 3rd, D., Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106,
RFC 4086, June 2005.
[SMALL-GROUP] Zuccherato, R., "Methods for Avoiding the "Small-
Subgroup" Attacks on the Diffie-Hellman Key Agreement
Method for S/MIME", RFC 2785, March 2000.
[X942] Rescorla, E., "Diffie-Hellman Key Agreement Method",
RFC 2631, June 1999.
[RFC2797] Myers, M., Liu, X., Schaad, J., and J. Weinstein,
"Certificate Management Messages over CMS", RFC 2797,
April 2000.
Schaad & Myers Standards Track [Page 64]RFC 5272 CMC: Structures June 2008
Appendix A. ASN.1 Module
EnrollmentMessageSyntax
{ iso(1) identified-organization(3) dod(4) internet(1)
security(5) mechansims(5) pkix(7) id-mod(0) id-mod-cmc2002(23) }
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
-- EXPORTS All --
-- The types and values defined in this module are exported for use
-- in the other ASN.1 modules. Other applications may use them for
-- their own purposes.
IMPORTS
-- PKIX Part 1 - Implicit From [PKIXCERT]
GeneralName, CRLReason, ReasonFlags
FROM PKIX1Implicit88 {iso(1) identified-organization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
id-pkix1-implicit(19)}
-- PKIX Part 1 - Explicit From [PKIXCERT]
AlgorithmIdentifier, Extension, Name, CertificateSerialNumber
FROM PKIX1Explicit88 {iso(1) identified-organization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
id-pkix1-explicit(18)}
-- Cryptographic Message Syntax FROM [CMS]
ContentInfo, Attribute, IssuerAndSerialNumber
FROM CryptographicMessageSyntax2004 { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
modules(0) cms-2004(24)}
-- CRMF FROM [CRMF]
CertReqMsg, PKIPublicationInfo, CertTemplate
FROM PKIXCRMF-2005 {iso(1) identified-organization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-crmf2005(36)};
-- Global Types
UTF8String ::= [UNIVERSAL 12] IMPLICIT OCTET STRING
-- The content of this type conforms to RFC 2279.
Schaad & Myers Standards Track [Page 65]RFC 5272 CMC: Structures June 2008
id-pkix OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
dod(6) internet(1) security(5) mechanisms(5) pkix(7) }
id-cmc OBJECT IDENTIFIER ::= {id-pkix 7} -- CMC controls
id-cct OBJECT IDENTIFIER ::= {id-pkix 12} -- CMC content types
-- The following controls have the type OCTET STRING
id-cmc-identityProof OBJECT IDENTIFIER ::= {id-cmc 3}
id-cmc-dataReturn OBJECT IDENTIFIER ::= {id-cmc 4}
id-cmc-regInfo OBJECT IDENTIFIER ::= {id-cmc 18}
id-cmc-responseInfo OBJECT IDENTIFIER ::= {id-cmc 19}
id-cmc-queryPending OBJECT IDENTIFIER ::= {id-cmc 21}
id-cmc-popLinkRandom OBJECT IDENTIFIER ::= {id-cmc 22}
id-cmc-popLinkWitness OBJECT IDENTIFIER ::= {id-cmc 23}
-- The following controls have the type UTF8String
id-cmc-identification OBJECT IDENTIFIER ::= {id-cmc 2}
-- The following controls have the type INTEGER
id-cmc-transactionId OBJECT IDENTIFIER ::= {id-cmc 5}
-- The following controls have the type OCTET STRING
id-cmc-senderNonce OBJECT IDENTIFIER ::= {id-cmc 6}
id-cmc-recipientNonce OBJECT IDENTIFIER ::= {id-cmc 7}
-- This is the content type used for a request message in the protocol
id-cct-PKIData OBJECT IDENTIFIER ::= { id-cct 2 }
PKIData ::= SEQUENCE {
controlSequence SEQUENCE SIZE(0..MAX) OF TaggedAttribute,
reqSequence SEQUENCE SIZE(0..MAX) OF TaggedRequest,
cmsSequence SEQUENCE SIZE(0..MAX) OF TaggedContentInfo,
otherMsgSequence SEQUENCE SIZE(0..MAX) OF OtherMsg
}
bodyIdMax INTEGER ::= 4294967295
BodyPartID ::= INTEGER(0..bodyIdMax)
Schaad & Myers Standards Track [Page 66]RFC 5272 CMC: Structures June 2008
TaggedAttribute ::= SEQUENCE {
bodyPartID BodyPartID,
attrType OBJECT IDENTIFIER,
attrValues SET OF AttributeValue
}
AttributeValue ::= ANY
TaggedRequest ::= CHOICE {
tcr [0] TaggedCertificationRequest,
crm [1] CertReqMsg,
orm [2] SEQUENCE {
bodyPartID BodyPartID,
requestMessageType OBJECT IDENTIFIER,
requestMessageValue ANY DEFINED BY requestMessageType
}
}
TaggedCertificationRequest ::= SEQUENCE {
bodyPartID BodyPartID,
certificationRequest CertificationRequest
}
CertificationRequest ::= SEQUENCE {
certificationRequestInfo SEQUENCE {
version INTEGER,
subject Name,
subjectPublicKeyInfo SEQUENCE {
algorithm AlgorithmIdentifier,
subjectPublicKey BIT STRING },
attributes [0] IMPLICIT SET OF Attribute },
signatureAlgorithm AlgorithmIdentifier,
signature BIT STRING
}
TaggedContentInfo ::= SEQUENCE {
bodyPartID BodyPartID,
contentInfo ContentInfo
}
OtherMsg ::= SEQUENCE {
bodyPartID BodyPartID,
otherMsgType OBJECT IDENTIFIER,
otherMsgValue ANY DEFINED BY otherMsgType }
Schaad & Myers Standards Track [Page 67]RFC 5272 CMC: Structures June 2008
-- This defines the response message in the protocol
id-cct-PKIResponse OBJECT IDENTIFIER ::= { id-cct 3 }
ResponseBody ::= PKIResponse
PKIResponse ::= SEQUENCE {
controlSequence SEQUENCE SIZE(0..MAX) OF TaggedAttribute,
cmsSequence SEQUENCE SIZE(0..MAX) OF TaggedContentInfo,
otherMsgSequence SEQUENCE SIZE(0..MAX) OF OtherMsg
}
-- Used to return status state in a response
id-cmc-statusInfo OBJECT IDENTIFIER ::= {id-cmc 1}
CMCStatusInfo ::= SEQUENCE {
cMCStatus CMCStatus,
bodyList SEQUENCE SIZE (1..MAX) OF BodyPartID,
statusString UTF8String OPTIONAL,
otherInfo CHOICE {
failInfo CMCFailInfo,
pendInfo PendInfo } OPTIONAL
}
PendInfo ::= SEQUENCE {
pendToken OCTET STRING,
pendTime GeneralizedTime
}
CMCStatus ::= INTEGER {
success (0),
failed (2),
pending (3),
noSupport (4),
confirmRequired (5),
popRequired (6),
partial (7)
}
-- Note:
-- The spelling of unsupportedExt is corrected in this version.
-- In RFC 2797, it was unsuportedExt.
Schaad & Myers Standards Track [Page 68]RFC 5272 CMC: Structures June 2008
CMCFailInfo ::= INTEGER {
badAlg (0),
badMessageCheck (1),
badRequest (2),
badTime (3),
badCertId (4),
unsupportedExt (5),
mustArchiveKeys (6),
badIdentity (7),
popRequired (8),
popFailed (9),
noKeyReuse (10),
internalCAError (11),
tryLater (12),
authDataFail (13)
}
-- Used for RAs to add extensions to certification requests
id-cmc-addExtensions OBJECT IDENTIFIER ::= {id-cmc 8}
AddExtensions ::= SEQUENCE {
pkiDataReference BodyPartID,
certReferences SEQUENCE OF BodyPartID,
extensions SEQUENCE OF Extension
}
id-cmc-encryptedPOP OBJECT IDENTIFIER ::= {id-cmc 9}
id-cmc-decryptedPOP OBJECT IDENTIFIER ::= {id-cmc 10}
EncryptedPOP ::= SEQUENCE {
request TaggedRequest,
cms ContentInfo,
thePOPAlgID AlgorithmIdentifier,
witnessAlgID AlgorithmIdentifier,
witness OCTET STRING
}
DecryptedPOP ::= SEQUENCE {
bodyPartID BodyPartID,
thePOPAlgID AlgorithmIdentifier,
thePOP OCTET STRING
}
id-cmc-lraPOPWitness OBJECT IDENTIFIER ::= {id-cmc 11}
Schaad & Myers Standards Track [Page 69]RFC 5272 CMC: Structures June 2008
LraPopWitness ::= SEQUENCE {
pkiDataBodyid BodyPartID,
bodyIds SEQUENCE OF BodyPartID
}
--
id-cmc-getCert OBJECT IDENTIFIER ::= {id-cmc 15}
GetCert ::= SEQUENCE {
issuerName GeneralName,
serialNumber INTEGER }
id-cmc-getCRL OBJECT IDENTIFIER ::= {id-cmc 16}
GetCRL ::= SEQUENCE {
issuerName Name,
cRLName GeneralName OPTIONAL,
time GeneralizedTime OPTIONAL,
reasons ReasonFlags OPTIONAL }
id-cmc-revokeRequest OBJECT IDENTIFIER ::= {id-cmc 17}
RevokeRequest ::= SEQUENCE {
issuerName Name,
serialNumber INTEGER,
reason CRLReason,
invalidityDate GeneralizedTime OPTIONAL,
passphrase OCTET STRING OPTIONAL,
comment UTF8String OPTIONAL }
id-cmc-confirmCertAcceptance OBJECT IDENTIFIER ::= {id-cmc 24}
CMCCertId ::= IssuerAndSerialNumber
-- The following is used to request V3 extensions be added to a
-- certificate
id-ExtensionReq OBJECT IDENTIFIER ::= {iso(1) member-body(2) us(840)
rsadsi(113549) pkcs(1) pkcs-9(9) 14}
ExtensionReq ::= SEQUENCE SIZE (1..MAX) OF Extension
-- The following exists to allow Diffie-Hellman Certification Requests
-- Messages to be well-formed
id-alg-noSignature OBJECT IDENTIFIER ::= {id-pkix id-alg(6) 2}
NoSignatureValue ::= OCTET STRING
Schaad & Myers Standards Track [Page 70]RFC 5272 CMC: Structures June 2008
-- Unauthenticated attribute to carry removable data.
-- This could be used in an update of "CMC Extensions: Server Side
-- Key Generation and Key Escrow" (February 2005) and in other
-- documents.
id-aa OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2)}
id-aa-cmc-unsignedData OBJECT IDENTIFIER ::= {id-aa 34}
CMCUnsignedData ::= SEQUENCE {
bodyPartPath BodyPartPath,
identifier OBJECT IDENTIFIER,
content ANY DEFINED BY identifier
}
-- Replaces CMC Status Info
--
id-cmc-statusInfoV2 OBJECT IDENTIFIER ::= {id-cmc 25}
CMCStatusInfoV2 ::= SEQUENCE {
cMCStatus CMCStatus,
bodyList SEQUENCE SIZE (1..MAX) OF
BodyPartReference,
statusString UTF8String OPTIONAL,
otherInfo CHOICE {
failInfo CMCFailInfo,
pendInfo PendInfo,
extendedFailInfo SEQUENCE {
failInfoOID OBJECT IDENTIFIER,
failInfoValue AttributeValue
}
} OPTIONAL
}
BodyPartReference ::= CHOICE {
bodyPartID BodyPartID,
bodyPartPath BodyPartPath
}
BodyPartPath ::= SEQUENCE SIZE (1..MAX) OF BodyPartID
Schaad & Myers Standards Track [Page 71]RFC 5272 CMC: Structures June 2008
-- Allow for distribution of trust anchors
--
id-cmc-trustedAnchors OBJECT IDENTIFIER ::= {id-cmc 26}
PublishTrustAnchors ::= SEQUENCE {
seqNumber INTEGER,
hashAlgorithm AlgorithmIdentifier,
anchorHashes SEQUENCE OF OCTET STRING
}
id-cmc-authData OBJECT IDENTIFIER ::= {id-cmc 27}
AuthPublish ::= BodyPartID
-- These two items use BodyPartList
id-cmc-batchRequests OBJECT IDENTIFIER ::= {id-cmc 28}
id-cmc-batchResponses OBJECT IDENTIFIER ::= {id-cmc 29}
BodyPartList ::= SEQUENCE SIZE (1..MAX) OF BodyPartID
--
id-cmc-publishCert OBJECT IDENTIFIER ::= {id-cmc 30}
CMCPublicationInfo ::= SEQUENCE {
hashAlg AlgorithmIdentifier,
certHashes SEQUENCE OF OCTET STRING,
pubInfo PKIPublicationInfo
}
id-cmc-modCertTemplate OBJECT IDENTIFIER ::= {id-cmc 31}
ModCertTemplate ::= SEQUENCE {
pkiDataReference BodyPartPath,
certReferences BodyPartList,
replace BOOLEAN DEFAULT TRUE,
certTemplate CertTemplate
}
-- Inform follow on servers that one or more controls have already been
-- processed
id-cmc-controlProcessed OBJECT IDENTIFIER ::= {id-cmc 32}
ControlsProcessed ::= SEQUENCE {
bodyList SEQUENCE SIZE(1..MAX) OF BodyPartReference
}
Schaad & Myers Standards Track [Page 72]RFC 5272 CMC: Structures June 2008
-- Identity Proof control w/ algorithm agility
id-cmc-identityProofV2 OBJECT IDENTIFIER ::= { id-cmc 34 }
IdentifyProofV2 ::= SEQUENCE {
proofAlgID AlgorithmIdentifier,
macAlgId AlgorithmIdentifier,
witness OCTET STRING
}
id-cmc-popLinkWitnessV2 OBJECT IDENTIFIER ::= { id-cmc 33 }
PopLinkWitnessV2 ::= SEQUENCE {
keyGenAlgorithm AlgorithmIdentifier,
macAlgorithm AlgorithmIdentifier,
witness OCTET STRING
}
END
Schaad & Myers Standards Track [Page 73]RFC 5272 CMC: Structures June 2008
Appendix B. Enrollment Message Flows
This section is informational. The purpose of this section is to
present, in an abstracted version, the messages that would flow
between the client and server for several different common cases.
B.1. Request of a Signing Certificate
This section looks at the messages that would flow in the event that
an enrollment is occurring for a signing-only key. If the
certificate was designed for both signing and encryption, the only
difference would be the key usage extension in the certification
request.
Message #2 from client to server:
ContentInfo.contentType = id-signedData
ContentInfo.content
SignedData.encapContentInfo
eContentType = id-ct-PKIData
eContent
controlSequence
{102, id-cmc-identityProof, computed value}
{103, id-cmc-senderNonce, 10001}
reqSequence
certRequest
certReqId = 201
certTemplate
subject = My Proposed DN
publicKey = My Public Key
extensions
{id-ce-subjectPublicKeyIdentifier, 1000}
{id-ce-keyUsage, digitalSignature}
SignedData.SignerInfos
SignerInfo
sid.subjectKeyIdentifier = 1000
Schaad & Myers Standards Track [Page 74]RFC 5272 CMC: Structures June 2008
Response from server to client:
ContentInfo.contentType = id-signedData
ContentInfo.content
SignedData.encapContentInfo
eContentType = id-ct-PKIResponse
eContent
controlSequence
{102, id-cmc-statusInfoV2, {success, 201}}
{103, id-cmc-senderNonce, 10005}
{104, id-cmc-recipientNonce, 10001}
certificates
Newly issued certificate
Other certificates
SignedData.SignerInfos
Signed by CA
B.2. Single Certification Request, But Modified by RA
This section looks at the messages that would flow in the event that
an enrollment has one RA in the middle of the data flow. That RA
will modify the certification request before passing it on to the CA.
Message from client to RA:
ContentInfo.contentType = id-signedData
ContentInfo.content
SignedData.encapContentInfo
eContentType = id-ct-PKIData
eContent
controlSequence
{102, id-cmc-identityProof, computed value}
{103, id-cmc-senderNonce, 10001}
reqSequence
certRequest
certReqId = 201
certTemplate
subject = My Proposed DN
publicKey = My Public Key
extensions
{id-ce-subjectPublicKeyIdentifier, 1000}
{id-ce-keyUsage, digitalSignature}
SignedData.SignerInfos
SignerInfo
sid.subjectKeyIdentifier = 1000
Schaad & Myers Standards Track [Page 75]RFC 5272 CMC: Structures June 2008
Message from RA to CA:
ContentInfo.contentType = id-signedData
ContentInfo.content
SignedData.encapContentInfo
eContentType = id-ct-PKIData
eContent
controlSequence
{ 102, id-cmc-batchRequests, { 1, 2} }
{ 103, id-cmc-addExtensions,
{ {1, 201, {id-ce-certificatePolicies, anyPolicy}}
{1, 201, {id-ce-subjectAltName, {extension data}}
{2, XXX, {id-ce-subjectAltName, {extension data}}}
The Value XXX is not known here; it would
reference into the second client request,
which is not displayed above.
cmsSequence
{ 1, <Message from client to RA #1> }
{ 2, <Message from client to RA #2> }
SignedData.SignerInfos
SignerInfo
sid = RA key.
Schaad & Myers Standards Track [Page 76]RFC 5272 CMC: Structures June 2008
Response from CA to RA:
ContentInfo.contentType = id-signedData
ContentInfo.content
SignedData.encapContentInfo
eContentType = id-ct-PKIResponse
eContent
controlSequence
{102, id-cmc-BatchResponse, {999, 998}}
{103, id-cmc-statusInfoV2, {failed, 2, badIdentity}}
cmsSequence
{ bodyPartID = 999
contentInfo
ContentInfo.contentType = id-signedData
ContentInfo.content
SignedData.encapContentInfo
eContentType = id-ct-PKIResponse
eContent
controlSequence
{102, id-cmc-statusInfoV2, {success, 201}}
certificates
Newly issued certificate
Other certificates
SignedData.SignerInfos
Signed by CA
}
{ bodyPartID = 998,
contentInfo
ContentInfo.contentType = id-signedData
ContentInfo.content
SignedData.encapContentInfo
eContentType = id-ct-PKIResponse
eContent
controlSequence
{102, id-cmc-statusInfoV2, {failure, badAlg}}
certificates
Newly issued certificate
Other certificates
SignedData.SignerInfos
Signed by CA
}
SignedData.SignerInfos
Signed by CA
Schaad & Myers Standards Track [Page 77]RFC 5272 CMC: Structures June 2008
Response from RA to client:
ContentInfo.contentType = id-signedData
ContentInfo.content
SignedData.encapContentInfo
eContentType = id-ct-PKIResponse
eContent
controlSequence
{102, id-cmc-statusInfoV2, {success, 201}}
certificates
Newly issued certificate
Other certificates
SignedData.SignerInfos
Signed by CA
B.3. Direct POP for an RSA Certificate
This section looks at the messages that would flow in the event that
an enrollment is done for an encryption only certificate using an
direct POP method. For simplicity, it is assumed that the
certification requester already has a signing-only certificate.
The fact that a second round-trip is required is implicit rather than
explicit. The server determines this based on the fact that no other
POP exists for the certification request.
Schaad & Myers Standards Track [Page 78]RFC 5272 CMC: Structures June 2008
Message #1 from client to server:
ContentInfo.contentType = id-signedData
ContentInfo.content
SignedData.encapContentInfo
eContentType = id-ct-PKIData
eContent
controlSequence
{102, id-cmc-transactionId, 10132985123483401}
{103, id-cmc-senderNonce, 10001}
{104, id-cmc-dataReturn, <packet of binary data identifying
where the key in question is.>}
reqSequence
certRequest
certReqId = 201
certTemplate
subject = <My DN from my signing cert>
publicKey = My Public Key
extensions
{id-ce-keyUsage, keyEncipherment}
popo
keyEncipherment
subsequentMessage
SignedData.SignerInfos
SignerInfo
Signed by requester's signing cert
Response #1 from server to client:
ContentInfo.contentType = id-signedData
ContentInfo.content
SignedData.encapContentInfo
eContentType = id-ct-PKIResponse
eContent
controlSequence
{101, id-cmc-statusInfoV2, {failed, 201, popRequired}}
{102, id-cmc-transactionId, 10132985123483401}
{103, id-cmc-senderNonce, 10005}
{104, id-cmc-recipientNonce, 10001}
{105, id-cmc-encryptedPOP, {
request {
certRequest
certReqId = 201
certTemplate
subject = <My DN from my signing cert>
publicKey = My Public Key
extensions
{id-ce-keyUsage, keyEncipherment}
Schaad & Myers Standards Track [Page 79]RFC 5272 CMC: Structures June 2008
popo
keyEncipherment
subsequentMessage
}
cms
contentType = id-envelopedData
content
recipientInfos.riid.issuerSerialNumber = <NULL, 201>
encryptedContentInfo
eContentType = id-data
eContent = <Encrypted value of 'y'>
thePOPAlgID = HMAC-SHA1
witnessAlgID = SHA-1
witness <hashed value of 'y'>}}
{106, id-cmc-dataReturn, <packet of binary data identifying
where the key in question is.>}
certificates
Other certificates (optional)
SignedData.SignerInfos
Signed by CA
ContentInfo.contentType = id-signedData
ContentInfo.content
SignedData.encapContentInfo
eContentType = id-ct-PKIData
eContent
controlSequence
{102, id-cmc-transactionId, 10132985123483401}
{103, id-cmc-senderNonce, 100101}
{104, id-cmc-dataReturn, <packet of binary data identifying
where the key in question is.>}
{105, id-cmc-recipientNonce, 10005}
{107, id-cmc-decryptedPOP, {
bodyPartID 201,
thePOPAlgID HMAC-SHA1,
thePOP <HMAC computed value goes here>}}
reqSequence
certRequest
certReqId = 201
certTemplate
subject = <My DN from my signing cert>
publicKey = My Public Key
extensions
{id-ce-keyUsage, keyEncipherment}
popo
keyEncipherment
subsequentMessage
Schaad & Myers Standards Track [Page 80]RFC 5272 CMC: Structures June 2008
SignedData.SignerInfos
SignerInfo
Signed by requester's signing cert
Response #2 from server to client:
ContentInfo.contentType = id-signedData
ContentInfo.content
SignedData.encapContentInfo
eContentType = id-ct-PKIResponse
eContent
controlSequence
{101, id-cmc-transactionId, 10132985123483401}
{102, id-cmc-statusInfoV2, {success, 201}}
{103, id-cmc-senderNonce, 10019}
{104, id-cmc-recipientNonce, 100101}
{105, id-cmc-dataReturn, <packet of binary data identifying
where the key in question is.>}
certificates
Newly issued certificate
Other certificates
SignedData.SignerInfos
Signed by CA
Appendix C. Production of Diffie-Hellman Public Key Certification
Requests
Part of a certification request is a signature over the request;
Diffie-Hellman is a key agreement algorithm and cannot be used to
directly produce the required signature object. [DH-POP] provides
two ways to produce the necessary signature value. This document
also defines a signature algorithm that does not provide a POP value,
but can be used to produce the necessary signature value.
C.1. No-Signature Signature Mechanism
Key management (encryption/decryption) private keys cannot always be
used to produce some type of signature value as they can be in a
decrypt-only device. Certification requests require that the
signature field be populated. This section provides a signature
algorithm specifically for that purposes. The following object
identifier and signature value are used to identify this signature
type:
id-alg-noSignature OBJECT IDENTIFIER ::= {id-pkix id-alg(6) 2}
NoSignatureValue ::= OCTET STRING
Schaad & Myers Standards Track [Page 81]RFC 5272 CMC: Structures June 2008
The parameters for id-alg-noSignature MUST be present and MUST be
encoded as NULL. NoSignatureValue contains the hash of the
certification request. It is important to realize that there is no
security associated with this signature type. If this signature type
is on a certification request and the Certification Authority policy
requires proof-of-possession of the private key, the POP mechanism
defined in Section 6.7 MUST be used.
Authors' Addresses
Jim Schaad
Soaring Hawk Consulting
PO Box 675
Gold Bar, WA 98251
Phone: (425) 785-1031
EMail: jimsch@nwlink.com
Michael Myers
TraceRoute Security, Inc.
EMail: mmyers@fastq.com
Schaad & Myers Standards Track [Page 82]
RFC 5272 CMC: Structures June 2008
Full Copyright Statement
Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Schaad & Myers Standards Track [Page 83]
