One document matched: draft-turner-asymmetrickeyformat-02.txt
Differences from draft-turner-asymmetrickeyformat-01.txt
Network Working Group Sean Turner, IECA
Internet Draft 20 October 2009
Intended Status: Standard Track
Updates: RFC 5208 (once approved)
Expires: 20 April 2010
Asymmetric Key Packages
draft-turner-asymmetrickeyformat-02.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 a specified public-key algorithm and a set of attributes. The
Cryptographic Message Syntax (CMS), as defined in RFC 3852, can be
used to digitally sign, digest, authenticate, or encrypt the
asymmetric key format content type. This document updates RFC 5208.
1. Introduction
This document defines the syntax for private key information and a
Cryptographic Message Syntax (CMS) [RFC5652] content type for it.
Private-key information includes a private key for a specified
public-key algorithm and a set of attributes. The CMS can be used to
digitally sign, digest, authenticate, or encrypt the asymmetric key
format content type. This document updates PKCS#8 v1.2 [RFC5208]
sections 5 and 7, and it adds two new sections; the first covers
protecting the Asymmetric Key Content Type, and the second discusses
compatibility with other private-key formats.
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. Summary of Updates to RFC 5208
The following summarizes the updates to [RFC5208]:
- Changed the name "PrivateKeyInfo" to "OneAsymmetricKey". This
reflects the addition of the public key field to allow both parts
of the asymmetric key to be conveyed separately. Not all
algorithms will use both fields; however, the publicKey field was
added for completeness.
- Defined Asymmetric Key Package CMS content type.
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- Removed redundant IMPLICIT from attributes.
- Added publicKey to OneAsymmetricKey and updated the version number.
- Added that PKCS#9 attributes may be supported.
- Added discussion of compatibility with other private-key formats.
- Added requirements for encoding rule set.
- Changed imports from PKCS#5 to [RFCTBD3].
2. Asymmetric Key Package CMS Content Type
This section updates section 5 of [RFC5208].
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). Earlier versions of this
specification [RFC5208] did not specify a particular encoding rule
set, but generators SHOULD use DER [X.690] and receivers SHOULD be
prepared to handle BER [X.690] and DER [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,
attributes [0] Attributes OPTIONAL,
publicKey [1] PublicKey OPTIONAL
}
PrivateKeyInfo ::= OneAsymmetricKey
-- PrivateKeyInfo is used by [P12]. If version is set to 1,
-- publicKey MUST be absent. When v1, PrivateKeyInfo is the same
-- as it was in [RFC5208].
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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.
PublicKey ::= BIT STRING
-- Content varies based on type of key. The
-- algorithm identifier dictates the format of
-- the key.
Attributes ::= Set of Attribute
The AsymmetricKeyPackage contains one or more OneAsymmetricKey
elements.
The syntax of OneAsymmetricKey accommodates a version number, an
indication of the asymmetric algorithm to be used with the private
key, a private key, optional keying material attributes (e.g.,
userCertificate from [X.520]), and an optional 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.
OneAsymmetricKey is a renamed extension of the PrivateKeyInfo syntax
defined in [RFC5208]. The new name better reflects the ability to
carry both private and public key components. Backwards
compatibility with the original PrivateKeyInfo is preserved via
version number. The fields in OneAsymmetricKey are used as follows:
- version identifies the version of OneAsymmetricKey. If publicKey
is present, then version is set 2 else version is set to 1.
- privateKeyAlgorithm identifies the private-key algorithm and
optionally contains parameters associated with the asymmetric key.
The algorithm is identified by an object identifier (OID) and the
format of the parameters depends on the OID. The value placed in
privateKeyAlgorithmIdentifier is the value an originator would
apply to indicate which algorithm is to be used with the private
key.
- 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 example, a DSA key
is an INTEGER, an RSA key is represented as RSAPrivateKey as
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defined in [RFC3447], and an ECC key is represented as ECPrivateKey
as defined in [RFCTBD2].
- 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. For example, a DSA key
is an INTEGER. Other documents may define additional private key
formats. Note that RSA public keys are included in RSAPrivateKey
(i.e., n and e are present), as per [RFC3447], and ECC public keys
are included in ECPrivateKey (i.e., in the publicKey field), as per
[RFCTBD2].
3. Protecting the AsymmetricKeyPackage
CMS protecting content types, [RFC5652] and [RFC5083], 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.
- 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.
4. Other Private-Key Format Considerations
This document defines the syntax and the semantics for a content type
that exchanges asymmetric private keys. There are two other formats
that have been used for the transport of asymmetric private keys:
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- Personal Information Exchange (PFX) Syntax Standard [P12], which is
more commonly referred to as PKCS #12 or simply P12, is a transfer
syntax for personal identity information, including private keys,
certificates, miscellaneous secrets, and extensions.
OneAsymmetricKey, PrivateKeyInfo, and EncryptedPrivateKeyInfo
[RFC5208] can be carried in a P12 message. The private key
information, OneAsymmetricKey and PrivateKeyInfo, are carried in
the P12 keyBag BAG-TYPE. EncryptedPrivateKeyInfo is carried in the
P12 pkcs8ShroudedKeyBag BAG-TYPE. In current implementations, the
file extensions .pfx and .p12 can be used interchangeably.
- Microsoft's private key proprietary transfer syntax. The .pvk file
extension is used for local storage.
The .pvk and .p12/.pfx formats are not interchangeable; however,
conversion tools exist to convert from one format to another.
[RFCTBD3] defines the appication/pkcs8 media type and .p8 file
extension.
To extract the private key information from the AsymmetricKeyPackage,
the encapsulating layers need to be removed. At a minimum, the outer
ContentInfo [RFC5652] layer needs to be removed. If the
AsymmetricKeyPackage is encapsulated in a SignedData [RFC5652], then
the SignedData and EncapsulatedContentInfo layers [RFC5652] also need
to be removed. The same is true for EnvelopedData, EncryptedData, and
AuthenticatedData all from [RFC5652] as well as AuthEnvelopedData
from [RFC5083]. Once all the outer layers are removed, there are as
many sets of private key information as there are OneAsymmetricKey
structures. OneAsymmetricKey and PrivateKeyInfo are the same
structure; therefore, either can be saved as a .p8 file or copied in
to the P12 KeyBack BAG-TYPE. Removing encapsulating security layers
will invalidate any signature and may expose the key to unauthorized
disclosure.
.p8 files are sometimes PEM encoded. When .p8 files are PEM encoded
they use the .pem file extension. PEM encoding is the Base64
encoding [RFC2045] of either the DER encoded EncryptedPrivateKeyInfo
sandwiched between:
-----BEGIN ENCRYPTED PRIVATE KEY-----
-----END ENCRYPTED PRIVATE KEY-----
or the PrivateKeyInfo or the OneAsymmetricKey sandwiched between:
-----BEGIN PRIVATE KEY-----
-----END PRIVATE KEY-----
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5. Security Considerations
The security considerations in [RFC5208] also apply to this document.
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.
6. IANA Considerations
None: All identifiers are already registered. Please remove this
section prior to publication as an RFC.
7. References
7.1. Normative References
[RFC2045] Freed, .N, and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", RFC
5652, September 2009.
[RFC5208] Kaliski, B., "PKCS #8: Private Key Information Syntax
Standard Version 1.2", RFC 5208, May 2008.
[RFCTBD1] Schaad, J., and P. Hoffman, "New ASN.1 Modules for PKIX",
draft-ietf-pkix-new-asn1-07.txt, work-in-progress.
[RFCTBD3] Jennings C., and J. Fischl "Certificate Management
Service for The Session Initiation Protocol (SIP)",
draft-ietf-sip-certs-09.txt, work-in-progress.
[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.
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[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).
7.2. 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.
[RFC5083] Housley, R., "Cryptographic Message Syntax (CMS)
Authenticated-Enveloped-Data Content Type", RFC 5083,
November 2007.
[X.520] ITU-T Recommendation X.520 (2005) | ISO/IEC 9594-6:2005,
Information technology - Open Systems Interconnection -
The Directory: Selected attribute types.
[RFCTBD2] Turner, S., and D. Brown, "EC Private Key Info
Structure", draft-turner-ecprivatekey-00.txt, work-in-
progress.
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
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IMPORTS NOTHING
Attribute{}, ATTRIBUTE
FROM PKIX-CommonTypes-2009 -- FROM [RFCTBD1]
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkixCommon-02(57) }
AlgorithmIdentifier{}
FROM AlgorithmInformation-2009 -- FROM [RFCTBD1]
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-algorithmInformation-02(58) }
;
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
OneAsymmetricKey ::= SEQUENCE {
version Version,
privateKeyAlgorithm PrivateKeyAlgorithmIdentifier,
privateKey PrivateKey,
attributes [0] Attributes OPTIONAL,
publicKey [1] PublicKey OPTIONAL
}
PrivateKeyInfo ::= OneAsymmetricKey
-- PrivateKeyInfo is used by [P12]. If version is set to 1,
-- publicKey MUST be absent. When v1, PrivateKeyInfo is the same
-- as it was in [RFC5208].
Version ::= INTEGER {v1(0), v2(1)} (v1, v2,...)
PrivateKeyAlgorithmIdentifier ::= AlgorithmIdentifier
{ { PrivateKeyAlgorithms } }
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PrivateKey ::= OCTET STRING
-- Content varies based on type of key. The
-- algorithm identifier dictates the format of
-- the key.
PublicKey ::= BIT STRING
-- Content varies based on type of key. The
-- algorithm identifier dictates the format of
-- the key.
Attributes ::= Set of Attribute { { SupportedAttributes } }
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 ::= {
... -- Extensible
}
END
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, Russ Housley, and Carl Wallace.
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Author's Address
Sean Turner
IECA, Inc.
3057 Nutley Street, Suite 106
Fairfax, VA 22031
USA
Email: turners@ieca.com
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