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Versions: 00 01 02 03 04 05 RFC 5958

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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   Copyright (c) 2009 IETF Trust and the persons identified as the
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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents in effect on the date of
   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
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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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