Network Working Group B. Kaliski
Request for Comments: 5208 EMC
Category: Informational May 2008
Public-Key Cryptography Standards (PKCS) #8:
Private-Key Information Syntax Specification Version 1.2
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
IESG Note
The IESG thanks RSA Laboratories for transferring change control to
the IETF. Enhancements to this specification that preserve backward
compatibility are expected in an upcoming IETF standards track
document.
Abstract
This document represents a republication of PKCS #8 v1.2 from RSA
Laboratories' Public Key Cryptography Standard (PKCS) series. Change
control is transferred to the IETF. The body of this document,
except for the security considerations section, is taken directly
from the PKCS #8 v1.2 specification.
This document describes a syntax for private-key information.
Table of Contents
1. Introduction ....................................................2
2. Definitions .....................................................2
3. Symbols and Abbreviations .......................................2
4. General Overview ................................................2
5. Private-Key Information Syntax ..................................3
6. Encrypted Private-Key Information Syntax ........................4
7. Security Considerations .........................................4
Appendix A. ASN.1 Syntax ...........................................5
Informative References .............................................6
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1. Introduction
This document describes a syntax for private-key information.
Private-key information includes a private key for some public-key
algorithm and a set of attributes. The document also describes a
syntax for encrypted private keys. A password-based encryption
algorithm (e.g., one of those described in [PKCS#5]) could be used to
encrypt the private-key information.
The intention of including a set of attributes is to provide a simple
way for a user to establish trust in information such as a
distinguished name or a top-level certification authority's public
key. While such trust could also be established with a digital
signature, encryption with a secret key known only to the user is
just as effective and possibly easier to implement. A non-exhaustive
list of attributes is given in [PKCS#9].
2. Definitions
For the purposes of this document, the following definitions apply.
AlgorithmIdentifier: A type that identifies an algorithm (by
object identifier) and any associated parameters. This type is
defined in [X.509].
ASN.1: Abstract Syntax Notation One, as defined in [X.208].
Attribute: A type that contains an attribute type (specified by
object identifier) and one or more attribute values. This type is
defined in [X.501].
BER: Basic Encoding Rules, as defined in [X.209].
3. Symbols and Abbreviations
No symbols or abbreviations are defined in this document.
4. General Overview
The next two sections specify private-key information syntax and
encrypted private-key information syntax.
This document exports two types: PrivateKeyInfo (Section 6) and
EncryptedPrivateKeyInfo (Section 7).
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5. Private-Key Information Syntax
This section gives the syntax for private-key information.
Private-key information shall have ASN.1 type PrivateKeyInfo:
PrivateKeyInfo ::= SEQUENCE {
version Version,
privateKeyAlgorithm PrivateKeyAlgorithmIdentifier,
privateKey PrivateKey,
attributes [0] IMPLICIT Attributes OPTIONAL }
Version ::= INTEGER
PrivateKeyAlgorithmIdentifier ::= AlgorithmIdentifier
PrivateKey ::= OCTET STRING
Attributes ::= SET OF Attribute
The fields of type PrivateKeyInfo have the following meanings:
version is the syntax version number, for compatibility with
future revisions of this document. It shall be 0 for this version
of the document.
privateKeyAlgorithm identifies the private-key algorithm. One
example of a private-key algorithm is PKCS #1's rsaEncryption
[PKCS#1].
privateKey is an octet string whose contents are the value of the
private key. The interpretation of the contents is defined in the
registration of the private-key algorithm. For an RSA private
key, for example, the contents are a BER encoding of a value of
type RSAPrivateKey.
attributes is a set of attributes. These are the extended
information that is encrypted along with the private-key
information.
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6. Encrypted Private-Key Information Syntax
This section gives the syntax for encrypted private-key information.
Encrypted private-key information shall have ASN.1 type
EncryptedPrivateKeyInfo:
EncryptedPrivateKeyInfo ::= SEQUENCE {
encryptionAlgorithm EncryptionAlgorithmIdentifier,
encryptedData EncryptedData }
EncryptionAlgorithmIdentifier ::= AlgorithmIdentifier
EncryptedData ::= OCTET STRING
The fields of type EncryptedPrivateKeyInfo have the following
meanings:
encryptionAlgorithm identifies the algorithm under which the
private-key information is encrypted. Two examples are PKCS #5's
pbeWithMD2AndDES-CBC and pbeWithMD5AndDES-CBC [PKCS#5].
encryptedData is the result of encrypting the private-key
information.
The encryption process involves the following two steps:
1. The private-key information is BER encoded, yielding an octet
string.
2. The result of step 1 is encrypted with the secret key to give
an octet string, the result of the encryption process.
7. Security Considerations
Protection of the private-key information is vital to public-key
cryptography. Disclosure of the private-key material to another
entity can lead to masquerades. The encryption algorithm used in the
encryption process must be as 'strong' as the key it is protecting.
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Appendix A. ASN.1 Syntax
PKCS-8 {iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-8(8)
modules(1) pkcs-8(1)}
-- $Revision: 1.5 $
-- This module has been checked for conformance with the ASN.1
-- standard by the OSS ASN.1 Tools
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
-- EXPORTS All --
-- All types and values defined in this module is exported for use in
-- other ASN.1 modules.
IMPORTS
informationFramework
FROM UsefulDefinitions {joint-iso-itu-t(2) ds(5) module(1)
usefulDefinitions(0) 3}
Attribute
FROM InformationFramework informationFramework
AlgorithmIdentifier, ALGORITHM-IDENTIFIER
FROM PKCS-5 {iso(1) member-body(2) us(840) rsadsi(113549)
pkcs(1) pkcs-5(5) modules(16) pkcs-5(1)};
-- Private-key information syntax
PrivateKeyInfo ::= SEQUENCE {
version Version,
privateKeyAlgorithm AlgorithmIdentifier {{PrivateKeyAlgorithms}},
privateKey PrivateKey,
attributes [0] Attributes OPTIONAL }
Version ::= INTEGER {v1(0)} (v1,...)
PrivateKey ::= OCTET STRING
Attributes ::= SET OF Attribute
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-- Encrypted private-key information syntax
EncryptedPrivateKeyInfo ::= SEQUENCE {
encryptionAlgorithm AlgorithmIdentifier {{KeyEncryptionAlgorithms}},
encryptedData EncryptedData
}
EncryptedData ::= OCTET STRING
PrivateKeyAlgorithms ALGORITHM-IDENTIFIER ::= {
... -- For local profiles
}
KeyEncryptionAlgorithms ALGORITHM-IDENTIFIER ::= {
... -- For local profiles
}
END
Informative References
[PKCS#1] RSA Laboratories. PKCS #1: RSA Encryption Standard. Version
1.5, November 1993.
[PKCS#5] RSA Laboratories. PKCS #5: Password-Based Encryption
Standard. Version 1.5, November 1993.
[PKCS#9] RSA Laboratories. PKCS #9: Selected Attribute Types.
Version 1.1, November 1993.
[X.208] CCITT. Recommendation X.208: Specification of Abstract
Syntax Notation One (ASN.1). 1988.
[X.209] CCITT. Recommendation X.209: Specification of Basic
Encoding Rules for Abstract Syntax Notation One (ASN.1).
1988.
[X.501] CCITT. Recommendation X.501: The Directory - Models. 1988.
[X.509] CCITT. Recommendation X.509: The Directory - Authentication
Framework. 1988.
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Author's Addresses
Burt Kaliski
EMC Corporation
176 South Street
Hopkinton, MA 01748
USA
EMail: kaliski_burt@emc.com
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RFC 5208 PKCS #8: Private-Key Information Syntax Standard May 2008
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