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Internet Engineering Task Force (IETF)                         S. TurnerRequest for Comments: 6160                                          IECACategory: Standards Track                                     April 2011ISSN: 2070-1721Algorithms for Cryptographic Message Syntax (CMS) Protectionof Symmetric Key Package Content TypesAbstract   This document describes the conventions for using several   cryptographic algorithms with the Cryptographic Message Syntax (CMS)   to protect the symmetric key package content type.  Specifically, it   includes conventions necessary to implement SignedData,   EnvelopedData, EncryptedData, and AuthEnvelopedData.Status of This Memo   This is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6160.Copyright Notice   Copyright (c) 2011 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Turner                       Standards Track                    [Page 1]

RFC 6160          Algorithms for Symmetric Key Packages       April 20111.  Introduction   This document describes the conventions for using several   cryptographic algorithms with the Cryptographic Message Syntax (CMS)   [RFC5652] to protect the symmetric key package content type defined   in [RFC6031].  Specifically, it includes conventions necessary to   implement the following CMS content types: SignedData [RFC5652],   EnvelopedData [RFC5652], EncryptedData [RFC5652], and   AuthEnvelopedData [RFC5083].  Familiarity with [RFC5083], [RFC5652],   [RFC5753], and [RFC6031] is assumed.   This document does not define any new algorithms; instead, it refers   to previously defined algorithms.1.1.  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].2.  SignedData   If an implementation supports SignedData, then it MUST support the   signature scheme RSA [RFC3370] and SHOULD support the signature   schemes RSA Probabilistic Signature Scheme (RSASSA-PSS) [RFC4056] and   Digital Signature Algorithm (DSA) [RFC3370].  Additionally,   implementations MUST support the hash function SHA-256 [RFC5754] in   concert with these signature schemes, and they SHOULD support the   hash function SHA-1 [RFC3370].  If an implementation supports   SignedData, then it MAY support Elliptic Curve Digital Signature   Algorithm (ECDSA) [RFC6090][RFC5753].3.  EnvelopedData   If an implementation supports EnvelopedData, then it MUST implement   key transport, and it MAY implement key agreement.   When key transport is used, RSA encryption [RFC3370] MUST be   supported, and RSA Encryption Scheme - Optimal Asymmetric Encryption   Padding (RSAES-OAEP) [RFC3560] SHOULD be supported.   When key agreement is used, Diffie-Hellman (DH) ephemeral-static   [RFC3370] MUST be supported.  When key agreement is used, Elliptic   Curve Diffie-Hellman (ECDH) [RFC6090][RFC5753] MAY be supported.Turner                       Standards Track                    [Page 2]

RFC 6160          Algorithms for Symmetric Key Packages       April 2011   Regardless of the key management technique choice, implementations   MUST support AES-128 Key Wrap with Padding [RFC5649] as the content-   encryption algorithm.  Implementations SHOULD support AES-256 Key   Wrap with Padding [RFC5649] as the content-encryption algorithm.   When key agreement is used, the same key-wrap algorithm MUST be used   for both key and content encryption.  If the content-encryption   algorithm is AES-128 Key Wrap with Padding, then the key-wrap   algorithm MUST be AES-128 Key Wrap with Padding [RFC5649].  If the   content-encryption algorithm is AES-256 Key Wrap with Padding, then   the key-wrap algorithm MUST be AES-256 Key Wrap with Padding   [RFC5649].4.  EncryptedData   If an implementation supports EncryptedData, then it MUST implement   AES-128 Key Wrap with Padding [RFC5649] and SHOULD implement AES-256   Key Wrap with Padding [RFC5649].   NOTE: EncryptedData requires that keys be managed by other means;   therefore, the only algorithm specified is the content-encryption   algorithm.5.  AuthEnvelopedData   If an implementation supports AuthEnvelopedData, then it MUST   implement the EnvelopedData recommendations except for the content-   encryption algorithm, which, in this case, MUST be AES-GCM [RFC5084];   the 128-bit version MUST be implemented, and the 256-bit version   SHOULD be implemented.  Implementations MAY also support AES-CCM   [RFC5084].6.  Public Key Sizes   The easiest way to implement SignedData, EnvelopedData, and   AuthEnvelopedData is with public key certificates [RFC5280].  If an   implementation supports RSA, RSASSA-PSS, DSA, RSAES-OAEP, or Diffie-   Hellman, then it MUST support key lengths from 1024-bit to 2048-bit,   inclusive.  If an implementation supports ECDSA or ECDH, then it MUST   support keys on P-256.7.  Security Considerations   The security considerations from [RFC3370], [RFC3560], [RFC4056],   [RFC5083], [RFC5084], [RFC5649], [RFC5652], [RFC5753], [RFC5754], and   [RFC6031] apply.Turner                       Standards Track                    [Page 3]

RFC 6160          Algorithms for Symmetric Key Packages       April 2011   The choice of content-encryption algorithms for this document was   based on [RFC5649]:      In the design of some high assurance cryptographic modules, it is      desirable to segregate cryptographic keying material from other      data.  The use of a specific cryptographic mechanism solely for      the protection of cryptographic keying material can assist in this      goal.   Unfortunately, there is no AES-GCM or AES-CCM mode that provides the   same properties.  If an AES-GCM and AES-CCM mode that provides the   same properties is defined, then this document will be updated to   adopt that algorithm.   [SP800-57] provides comparable bits of security for some algorithms   and key sizes.  [SP800-57] also provides time frames during which   certain numbers of bits of security are appropriate, and some   environments may find these time frames useful.8.  References8.1.  Normative References   [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate               Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC3370]   Housley, R., "Cryptographic Message Syntax (CMS)               Algorithms",RFC 3370, August 2002.   [RFC3560]   Housley, R., "Use of the RSAES-OAEP Key Transport               Algorithm in Cryptographic Message Syntax (CMS)",RFC3560, July 2003.   [RFC4056]   Schaad, J., "Use of the RSASSA-PSS Signature Algorithm in               Cryptographic Message Syntax (CMS)",RFC 4056, June 2005.   [RFC5083]   Housley, R., "Cryptographic Message Syntax (CMS)               Authenticated-Enveloped-Data Content Type",RFC 5083,               November 2007.   [RFC5084]   Housley, R., "Using AES-CCM and AES-GCM Authenticated               Encryption in the Cryptographic Message Syntax (CMS)",RFC 5084, November 2007.   [RFC5280]   Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,               Housley, R., and W. Polk, "Internet X.509 Public Key               Infrastructure Certificate and Certificate Revocation               List (CRL) Profile",RFC 5280, May 2008.Turner                       Standards Track                    [Page 4]

RFC 6160          Algorithms for Symmetric Key Packages       April 2011   [RFC5649]   Housley, R. and M. Dworkin, "Advanced Encryption Standard               (AES) Key Wrap with Padding Algorithm",RFC 5649,               September 2009.   [RFC5652]   Housley, R., "Cryptographic Message Syntax (CMS)", STD               70,RFC 5652, September 2009.   [RFC5753]   Turner, S. and D. Brown, "Use of Elliptic Curve               Cryptography (ECC) Algorithms in Cryptographic Message               Syntax (CMS)",RFC 5753, January 2010.   [RFC5754]   Turner, S., "Using SHA2 Algorithms with Cryptographic               Message Syntax",RFC 5754, January 2010.   [RFC6031]   Turner, S. and R. Housley, "Cryptographic Message Syntax               (CMS) Symmetric Key Package Content Type",RFC 6031,               December 2010.   [RFC6090]   McGrew, D., Igoe, K., and M. Salter, "Fundamental               Elliptic Curve Cryptography Algorithms",RFC 6090,               February 2011.8.2.  Informative Reference   [SP800-57]  National Institute of Standards and Technology (NIST),               Special Publication 800-57: Recommendation for Key               Management - Part 1 (Revised), March 2007.Author's Address   Sean Turner   IECA, Inc.   3057 Nutley Street, Suite 106   Fairfax, VA 22031   USA   EMail: turners@ieca.comTurner                       Standards Track                    [Page 5]