Network Working Group Sean Turner, IECA Internet Draft 20 October 2008 Intended Status: Standard Track Obsoletes: RFC 5208 (once approved) Expires: 20 April 2009 Asymmetric Key Packages draft-turner-asymmetrickeyformat-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." 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 2009. Copyright Notice Copyright (C) The IETF Trust (2008). 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 Turner Expires 20 April 2009 [Page 1]
Internet-Draft Asymmetric Key Packages October 2008 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.....................................4 4. Protecting the AsymmetricKeyPackage............................5 5. Other Considerations...........................................5 6. Security Considerations........................................6 7. IANA Considerations............................................6 8. References.....................................................6 8.1. Normative References......................................6 8.2. Non-Normative References..................................7 APPENDIX A: ASN.1 Module..........................................8 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 [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. Turner Expires 20 April 2009 [Page 2]
Internet-Draft Asymmetric Key Packages October 2008 - 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 Content Type The asymmetric key package 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 aKeyAttrs [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 is INTEGER, ECDSA is INTEGER PublicKey ::= OCTET STRING -- Content varies based on type of key. The -- algorithm identifier dictates the format of -- the key. DSA is INTEGER, ECDSA is OCTET STRING Turner Expires 20 April 2009 [Page 3]
Internet-Draft Asymmetric Key Packages October 2008 Attributes ::= Set of Attribute The AsymmetricKeyPackage contains one or more OneAsymmetricKey elements. The syntax accommodates keying material attributes (e.g., certificates), a private key, an optional public key and optional asymmetric algorithm parameters. 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 are 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. 3. Encrypted Private Key Info This section gives the syntax for encrypted private-key information, which is used with the [P12]. Encrypted private-key information shall have ASN.1 type EncryptedPrivateKeyInfo: EncryptedPrivateKeyInfo ::= SEQUENCE { encryptionAlgorithm EncryptionAlgorithmIdentifier, encryptedData EncryptedData } Turner Expires 20 April 2009 [Page 4]
Internet-Draft Asymmetric Key Packages October 2008 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 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] 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 encapsulate 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. 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: Turner Expires 20 April 2009 [Page 5]
Internet-Draft Asymmetric Key Packages October 2008 - 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. 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. Turner Expires 20 April 2009 [Page 6]
Internet-Draft Asymmetric Key Packages October 2008 [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. [RFC5208] Kaliski, B., "PKCS #8: Private Key Information Syntax Standard Version 1.2", RFC 5208, May 2008. Turner Expires 20 April 2009 [Page 7]
Internet-Draft Asymmetric Key Packages October 2008 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 Turner Expires 20 April 2009 [Page 8]
Internet-Draft Asymmetric Key Packages October 2008 OneAsymmetricKey ::= SEQUENCE { version Version, privateKeyAlgorithm PrivateKeyAlgorithmIdentifier, privateKey PrivateKey, -- DER encoded aKeyAttrs [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 } EncAsymmetricKeyPackage ::= SEQUENCE SIZE (1..MAX) OF EncryptedPrivateKeyInfo 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 Turner Expires 20 April 2009 [Page 9]
Internet-Draft Asymmetric Key Packages October 2008 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 Turner Expires 20 April 2009 [Page 10]
Internet-Draft Asymmetric Key Packages October 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf- ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Turner Expires 20 April 2009 [Page 11]
