Internet Engineering Task Force (IETF)                         S. Turner
Request for Comments: 6033                                          IECA
Category: Standards Track                                  December 2010
ISSN: 2070-1721


          Algorithms for Cryptographic Message Syntax (CMS)
                  Encrypted Key Package Content Type

Abstract

  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 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/rfc6033.

Copyright Notice

  Copyright (c) 2010 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.






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RFC 6033        Algorithms for CMS Encrypted Key Packages  December 2010


1.  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].




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RFC 6033        Algorithms for CMS Encrypted Key Packages  December 2010


3.  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 material



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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.  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.

  [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.





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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: [email protected]





























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