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rfc:rfc6160

Internet Engineering Task Force (IETF) S. Turner Request for Comments: 6160 IECA Category: Standards Track April 2011 ISSN: 2070-1721

    Algorithms for Cryptographic Message Syntax (CMS) Protection
               of Symmetric Key Package Content Types

Abstract

 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 in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://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 to BCP 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 2011

1. 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. References

8.1. 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)", RFC
             3560, 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.com

Turner Standards Track [Page 5]

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