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 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. 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The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on 20 April 2010. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. Turner Expires 20 April 2010 [Page 1] Internet-Draft Asymmetric Key Packages October 2009 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 and restrictions with respect to this document. 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. Turner Expires 20 April 2010 [Page 2] Internet-Draft Asymmetric Key Packages October 2009 - 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]. Turner Expires 20 April 2010 [Page 3] Internet-Draft Asymmetric Key Packages October 2009 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 Turner Expires 20 April 2010 [Page 4] Internet-Draft Asymmetric Key Packages October 2009 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: Turner Expires 20 April 2010 [Page 5] Internet-Draft Asymmetric Key Packages October 2009 - 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----- Turner Expires 20 April 2010 [Page 6] Internet-Draft Asymmetric Key Packages October 2009 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. Turner Expires 20 April 2010 [Page 7] Internet-Draft Asymmetric Key Packages October 2009 [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 Turner Expires 20 April 2010 [Page 8] Internet-Draft Asymmetric Key Packages October 2009 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 } } Turner Expires 20 April 2010 [Page 9] Internet-Draft Asymmetric Key Packages October 2009 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. Turner Expires 20 April 2010 [Page 10] Internet-Draft Asymmetric Key Packages October 2009 Author's Address Sean Turner IECA, Inc. 3057 Nutley Street, Suite 106 Fairfax, VA 22031 USA Email: turners@ieca.com Turner Expires 20 April 2010 [Page 11]