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Internet Engineering Task Force (IETF)                         S. TurnerRequest for Comments: 6033                                          IECACategory: Standards Track                                  December 2010ISSN: 2070-1721Algorithms for Cryptographic Message Syntax (CMS)Encrypted Key Package Content TypeAbstract   This document describes the conventions for using several   cryptographic algorithms with the Cryptographic Message Syntax (CMS)   encrypted key package content type.  Specifically, it includes   conventions necessary to implement 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/rfc6033.Copyright Notice   Copyright (c) 2010 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 6033        Algorithms for CMS Encrypted Key Packages  December 20101.  Introduction   This document describes the conventions for using several   cryptographic algorithms with the Cryptographic Message Syntax (CMS)   encrypted key package content type [RFC6032].  Specifically, it   includes conventions necessary to implement the following CMS content   types: EnvelopedData [RFC5652], EncryptedData [RFC5652], and   AuthEnvelopedData [RFC5083].   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.  EnvelopedData   EnvelopedData [RFC5652] supports a number of key management   techniques.  Implementations that claim conformance to this document   MUST support the key transport mechanisms and SHOULD support the key   agreement mechanisms as defined below.  Other techniques MAY be   supported.   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, Ephemeral-Static Diffie-Hellman (DH)   [RFC3370] MUST be supported.   Since the content type is used to carry a cryptographic key and its   attributes, an algorithm that is traditionally used to encrypt one   key with another is employed.  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, a key wrap algorithm is also specified to   wrap the content-encryption key.  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].Turner                       Standards Track                    [Page 2]

RFC 6033        Algorithms for CMS Encrypted Key Packages  December 20103.  EncryptedData   EncryptedData [RFC5652] requires that keys be managed by other means;   therefore, the only algorithm specified is the content-encryption   algorithm.  Since the content type is used to carry a cryptographic   key and its attributes, an algorithm that is traditionally used to   encrypt one key with another is employed.  Implementations MUST   support AES-128 Key Wrap with Padding [RFC5649].  Implementations   SHOULD support AES-256 Key Wrap with Padding [RFC5649].4.  AuthEnvelopedData   AuthEnvelopedData [RFC5083], like EnvelopedData, supports a number of   key management techniques.  The key management requirements for   AuthEnvelopedData are the same as for EnvelopedData.  The difference   is the content-encryption algorithm.  Implementations MUST support   128-bit AES-Galois/Counter Mode (AES-GCM) [RFC5084] and SHOULD   support 256-bit AES-GCM [RFC5084].  Implementations MAY also support   AES-Counter with CBC-MAC (AES-CCM) [RFC5084].5.  Signed Data   Implementations of SignedData [RFC5652] MUST support the signature   scheme RSA [RFC3370] [RFC5754] and SHOULD support the signature   schemes RSA Probabilistic Signature Scheme (RSASSA-PSS) [RFC4056] and   Digital Signature Algorithm (DSA) [RFC3370] [RFC5754].  Additionally,   implementations MUST support in concert with these signature schemes   the hash function SHA-256 [RFC5754] and it SHOULD support the hash   function SHA-1 [RFC3370].6.  Public Key Sizes   The easiest way to implement SignedData, EnvelopedData, and   AuthEnvelopedData is with public key certificates [RFC5280].  If an   implementation supports RSA, RSAES-OAEP, DH, RSASSA-PSS, or DSA, then   it MUST support key lengths from 1024 bits to 2048 bits, inclusive.7.  Security Considerations   The security considerations from [RFC3370], [RFC3560], [RFC4056],   [RFC5083], [RFC5084], [RFC5649], [RFC5652], [RFC5754], and [RFC6032]   apply.   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 materialTurner                       Standards Track                    [Page 3]

RFC 6033        Algorithms for CMS Encrypted Key Packages  December 2010   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.   [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.Turner                       Standards Track                    [Page 4]

RFC 6033        Algorithms for CMS Encrypted Key Packages  December 2010   [RFC5754]   Turner, S., "Using SHA2 Algorithms with Cryptographic               Message Syntax",RFC 5754, January 2010.   [RFC6032]   Turner, S. and R. Housley, "Cryptographic Message Syntax               (CMS) Encrypted Key Package Content Type",RFC 6032,               December 2010.8.2. Informative References   [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]