Network Working Group Sean Turner, IECA
Internet Draft 30 October 2008
Intended Status: Standard Track
Obsoletes: RFC 5208 (once approved)
Expires: 30 April 2009
Asymmetric Key Packages
draft-turner-asymmetrickeyformat-01.txt
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Abstract
This document defines the syntax for private key information and a
content type for it. 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. The
Cryptographic Message Syntax, as defined in RFC 3852, can be used to
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digitally sign, digest, authenticate, or encrypt the asymmetric key
format content type. This document obsoletes RFC 5208.
Table of Contents
1. Introduction...................................................2
1.1. Requirements Terminology..................................2
1.2. ASN.1 Syntax Notation.....................................2
1.3. Changes since RFC 5208....................................2
2. Asymmetric Key Package Content Type............................3
3. Encrypted Private Key Info.....................................5
4. Protecting the AsymmetricKeyPackage............................5
5. Other Considerations...........................................6
6. Security Considerations........................................6
7. IANA Considerations............................................7
8. References.....................................................7
8.1. Normative References......................................7
8.2. Non-Normative References..................................7
APPENDIX A: ASN.1 Module..........................................9
1. Introduction
This document defines the syntax for private key information and a
content type for it. 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. The
Cryptographic Message Syntax [RFC3852] can be used to digitally sign,
digest, authenticate, or encrypt the asymmetric key format content
type. This document obsoletes PKCS#8 v1.2 [RFC5208].
1.1. 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].
1.2. ASN.1 Syntax Notation
The key package is defined using ASN.1 [X.680], [X.681], [X.682], and
[X.683].
1.3. Changes since RFC 5208
The following are the changes since [RFC5208]:
- Defined Asymmetric Key Package CMS content type.
- Removed IMPLICIT from aKeyAttrs to align text with module.
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- Added public key to OneAsymmetricKey and added new version number.
- Added that PKCS#9 attributes MAY be supported.
- Added Other Considerations section.
2. Asymmetric Key Package CMS Content Type
The asymmetric key package CMS content type is used to transfer one
or more plaintext asymmetric keys from one party to another. An
asymmetric key package MAY be encapsulated in one or more CMS
protecting content types (see Section 4). This content type MUST be
DER encoded [X.690].
The asymmetric key package content type has the following syntax:
PKCS7-CONTENT-TYPE ::= TYPE-IDENTIFIER
asymmetric-key-package PKCS7-CONTENT-TYPE ::=
{ AsymmetricKeyPackage IDENTIFIED BY id-ct-KP-aKeyPackage }
id-ct-KP-aKeyPackage OBJECT IDENTIFIER ::= |
{ TBD }
AsymmetricKeyPackage ::= SEQUENCE SIZE (1..MAX) OF OneAsymmetricKey
OneAsymmetricKey ::= SEQUENCE {
version Version,
privateKeyAlgorithm PrivateKeyAlgorithmIdentifier,
privateKey PrivateKey, -- DER encoded
attributes [0] Attributes OPTIONAL,
publicKey [1] PublicKey OPTIONAL }
PrivateKeyInfo ::= OneAsymmetricKey -- Used in [P12]
Version ::= INTEGER { v1(0), v2(1) } (v1, v2,...)
PrivateKeyAlgorithmIdentifier ::= AlgorithmIdentifier
{ { PrivateKeyAlgorithms } }
PrivateKey ::= OCTET STRING
-- Content varies based on type of key. The
-- algorithm identifier dictates the format of
-- the key. DSA's is an INTEGER ECDSA's is an
-- INTEGER, and RSA is as per [RFC3447].
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PublicKey ::= OCTET STRING
-- Content varies based on type of key. The
-- algorithm identifier dictates the format of
-- the key. DSA is an INTEGER, ECDSA is an OCTET
-- STRING, and RSA is a sequence of two INTEGERs
-- [PKI-ALG].
Attributes ::= Set of Attribute
The AsymmetricKeyPackage contains one or more OneAsymmetricKey
elements. The syntax of OneAsymmetricKey accommodates a version
number, an indication of the algorithm to be used with the private
key, a private key, and optionally keying material attributes (e.g.,
certificates) and a public key. In general, either the public key or
the certificate will be present. In very rare cases will both the
public key and the certificate be present as this includes two copies
of the public key. The fields in OneAsymmetricKey are used as
follows:
- version identifies version of the asymmetric key package content
structure. For this version of the specification, version MUST be
v1 if the publicKey field is absent and it MUST be set to v2 if the
publicKey field is present.
- privateKeyAlgorithm identifies the private key algorithm and
optionally contains parameters associated with the asymmetric key.
The algorithm is identified by an OID and the parameters format
depends on the OID. The value placed in
privateKeyAlgorithmIdentifier is the value an originator would
apply to indicate which algorithm was used.
- privateKey is an OCTET STRING whose contents is the DER encoded
private key. The interpretation of the contents is defined in the
registration of the private-key algorithm.
- attributes is optional. It contains information corresponding to
the public key (e.g., certificates). The attributes field uses the
class ATTRIBUTE which is restricted by the SupportedAttributes
parameterized type. SupportedAttributes is an open ended set in
this document. Others documents can constrain these values.
Attributes from [RFC2985] MAY be supported.
- publicKey is optional. When present, it contains the public key
encoded as an OCTET STRING. The structure within the octet string,
if any, depends on the privateKeyAlgorithm.
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3. Encrypted Private Key Info
This section gives the syntax for encrypted private-key information,
which is used with [P12].
Encrypted private-key information shall have ASN.1 type
EncryptedPrivateKeyInfo:
EncryptedPrivateKeyInfo ::= SEQUENCE {
encryptionAlgorithm EncryptionAlgorithmIdentifier,
encryptedData EncryptedData }
EncryptionAlgorithmIdentifier ::= AlgorithmIdentifier
{ { KeyEncryptionAlgorithms } }
EncryptedData ::= OCTET STRING
The EncAsymmetricKeyPackage contains one or more
EncryptedPrivateKeyInfo elements. The fields in
EncryptedPrivateKeyInfo are used as follows:
- encryptionAlgorithm identifies the algorithm under which the
private-key information is encrypted. Implementations MUST support
the TBD algorithm.
- encryptedData is the result of encrypting the private-key
information (i.e., the PrivateKeyInfo).
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.
4. Protecting the AsymmetricKeyPackage
CMS [RFC3852] and [RFC5083] protecting content types can be used to
provide security to the AsymmetricKeyPackage:
- SignedData can be used to apply a digital signature to the
AsymmetricKeyPackage.
- EncryptedData can be used to encrypt the AsymmetricKeyPackage to
provide confidentiality but does not distribute the content
encryption keys.
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- EnvelopedData can be used to encrypt the AsymmetricKeyPackage with
simple symmetric encryption, where the sender and the receiver
already share the necessary encryption key.
- AuthenticatedData can be used to protect the AsymmetricKeyPackage
with message authentication codes, where key management information
is handled in a manner similar to EnvelopedData.
- AuthEnvelopedData can be used to protect the AsymmetricKeypackage
with algorithms that support authenticated encryption, where key
management information is handled in a manner similar to
EnvelopedData.
5. Other Considerations
This document defines the syntax and the semantics for content types
that exchange asymmetric keys. There are two other standards for
transporting asymmetric private keys:
- Personal Information Exchange (PFX) or more commonly referred to as
P12 [P12], is a transfer syntax for personal identity information,
including private keys, certificates, miscellaneous secrets, and
extensions. Both PrivateKeyInfo and EncryptedPrivateKeyInfo can be
carried in a P12 message.
- Microsoft's Exchange Security format, which is a proprietary
format.
When locally storing private keys, the file format is either a DER
encoded file with the file extension .p12 or a PEM encoded file with
the file extension .pem.
When the private key is a character string, the OCTET STRING contains
an embedded UTF8String.
6. 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.
The asymmetric key package contents are not protected. This content
type can be combined with a security protocol to protect the contents
of the package.
The encrypted asymmetric key package contents are protected; as noted
above the encryption algorithm must be as 'strong' as the key it is
protecting.
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7. IANA Considerations
None: All identifiers are already registered. Please remove this
section prior to publication as an RFC.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3852] Housley, R., "Cryptographic Message Syntax (CMS)", RFC3852,
July 2004.
[X.680] ITU-T Recommendation X.680 (2002) | ISO/IEC 8824-1:2002.
Information Technology - Abstract Syntax Notation One.
[X.681] ITU-T Recommendation X.681 (2002) | ISO/IEC 8824-2:2002.
Information Technology - Abstract Syntax Notation One: Information
Object Specification.
[X.682] ITU-T Recommendation X.682 (2002) | ISO/IEC 8824-3:2002.
Information Technology - Abstract Syntax Notation One: Constraint
Specification.
[X.683] ITU-T Recommendation X.683 (2002) | ISO/IEC 8824-4:2002.
Information Technology - Abstract Syntax Notation One:
Parameterization of ASN.1 Specifications.
[X.690] ITU-T Recommendation X.690 (2002) | ISO/IEC 8825-1:2002.
Information Technology - ASN.1 encoding rules: Specification of Basic
Encoding Rules (BER), Canonical Encoding Rules (CER) and
Distinguished Encoding Rules (DER).
8.2. Non-Normative References
[P12] RSA Laboratories, "PKCS #12 v1.0: Personal Information Exchange
Syntax", June 1999.
[RFC2985] Nystrom, M., and B. Kaliski, "PKCS #9: Selected Object
Classes and Attribute Types Version 2.0", RFC 2985, November 2000.
[RFC3447] Jonsson, J., and B. Kaliski, " Public-Key Cryptography
Standards (PKCS) #1: RSA Cryptography Specifications Version 2.1",
RFC 3447, February 2003.
[RFC5208] Kaliski, B., "PKCS #8: Private Key Information Syntax
Standard Version 1.2", RFC 5208, May 2008.
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[RFC5083] Housley, R., "Cryptographic Message Syntax (CMS)
Authenticated-Enveloped-Data Content Type", RFC 5083, November 2007.
[PKI-ALG] Turner, S., Brown, D., Yiu, K., Housley, R., and T. Polk,
"Elliptic Curve Cryptography Subject Public Key Information", draft-
ietf-pkix-ecc-subpubkeyinfo, work-in-progress.
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APPENDIX A: ASN.1 Module
This annex provides the normative ASN.1 definitions for the
structures described in this specification using ASN.1 as defined in
[X.680] through [X.683].
AsymmetricKeyPackageModulev1 { tbd }
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
-- EXPORTS ALL
IMPORTS NOTHING
Attribute{}, ATTRIBUTE, AlgorithmIdentifier{}
FROM PKIX-CommonTypes
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkixCommon(43) }
id-aes128-wrap, id-aes192-wrap, id-aes1256-wrap
FROM CMSAesRsaesOaep
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
pkcs-9(9) smime(16) modules(0) id-mod-cms-aes(19) }
;
PKCS7-CONTENT-TYPE ::= TYPE-IDENTIFIER
KeyPackageContentTypes PKCS7-CONTENT-TYPE ::= {
asymmetric-key-package |
... -- Expect additional content types --
}
asymmetric-key-package PKCS7-CONTENT-TYPE ::=
{ AsymmetricKeyPackage IDENTIFIED BY id-ct-KP-aKeyPackage }
id-ct-KP-aKeyPackage OBJECT IDENTIFIER ::=
{ TBD }
AsymmetricKeyPackage ::= SEQUENCE SIZE (1..MAX) OF OneAsymmetricKey
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OneAsymmetricKey ::= SEQUENCE {
version Version,
privateKeyAlgorithm PrivateKeyAlgorithmIdentifier,
privateKey PrivateKey, -- DER encoded
attributes [0] Attributes OPTIONAL,
publicKey [1] PublicKey OPTIONAL }
PrivateKeyInfo ::= OneAsymmetricKey
Version ::= INTEGER {v1(0), v2(1)} (v1, v2,...)
PrivateKeyAlgorithmIdentifier ::= AlgorithmIdentifier
{ { PrivateKeyAlgorithms } }
PrivateKey ::= OCTET STRING -- Content varies based on type of key
-- DSA is INTEGER, ECDSA is ECPublicKey
PublicKey ::= OCTET STRING
Attributes ::= Set of Attribute { { SupportAttributes } }
SupportedAttributes ATTRIBUTE :: {
... -- For local profiles
}
EncryptedPrivateKeyInfo ::= SEQUENCE {
encryptionAlgorithm EncryptionAlgorithmIdentifier,
encryptedData EncryptedData }
EncryptionAlgorithmIdentifier ::= AlgorithmIdentifier
{ { KeyEncryptionAlgorithms } }
EncryptedData ::= OCTET STRING -- Encrypted PrivateKeyInfo
PrivateKeyAlgorithms ALGORITHM-IDENTIFIER ::= {
... -- Extensible
}
KeyEncryptionAlgorithms ALGORITHM-IDENTIFIER ::= {
id-aes128-wrap |
id-aes192-wrap |
id-aes256-wrap,
... -- Extensible
}
END
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Acknowledgements
Many thanks go out to the Burt Kaliski and Jim Randall at RSA.
Without the prior version of the document, this one wouldn't exist.
We'd also like to thank Pasi Eronen and Russ Housley.
Author's Address
Sean Turner
IECA, Inc.
3057 Nutley Street, Suite 106
Fairfax, VA 22031
USA
Email: turners@ieca.com
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