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rfc:rfc7192

Internet Engineering Task Force (IETF) S. Turner Request for Comments: 7192 IECA Category: Standards Track April 2014 ISSN: 2070-1721

         Algorithms for Cryptographic Message Syntax (CMS)
            Key Package Receipt and Error Content Types

Abstract

 This document describes the conventions for using several
 cryptographic algorithms with the Cryptographic Message Syntax (CMS)
 key package receipt and error content types.  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/rfc7192.

Copyright Notice

 Copyright (c) 2014 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 7192 Algs for CMS Key Package Rcpt Content Type April 2014

1. Introduction

 This document describes the conventions for using several
 cryptographic algorithms with the Cryptographic Message Syntax (CMS)
 key package receipt and error content types [RFC7191].  Specifically,
 it includes conventions necessary to implement SignedData [RFC5652],
 EnvelopedData [RFC5652], EncryptedData [RFC5652], and
 AuthEnvelopedData [RFC5083].
 This document does not define any new algorithms; instead, it refers
 to previously defined algorithms.  In fact, the algorithm
 requirements in this document are the same as those in [RFC5959],
 [RFC6033], [RFC6160], [RFC6161], and [RFC6162] with the following
 exceptions: the content-encryption algorithm is AES in Cipher Block
 Chaining (CBC) mode as opposed to AES Key Wrap with Message Length
 Indicator (MLI) and the key-wrap algorithm is AES Key Wrap as opposed
 to AES Key Wrap with MLI.  The rationale for the difference is that
 the receipt and error content types are not keys; therefore, AES Key
 Wrap with MLI is not appropriate for the content-encryption
 algorithm.  If an implementation is not using AES Key Wrap with MLI
 as the content-encryption algorithm, then there's no need to keep the
 key-wrap algorithm the same as the content encryption algorithm.
 NOTE: [RFC7191] only requires that the key package receipt be signed.

1.1. Terminology

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "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].  Implementations can also choose the
 to support Elliptic Curve Digital Signature Algorithm (ECDSA)
 [RFC5753] and [RFC6090].

Turner Standards Track [Page 2] RFC 7192 Algs for CMS Key Package Rcpt Content Type April 2014

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) [RFC5753] [RFC6090] MAY be supported.
 Regardless of the key management technique choice, implementations
 MUST support AES-128 in CBC mode [AES] as the content-encryption
 algorithm.  Implementations SHOULD support AES-256 in CBC mode [AES]
 as the content-encryption algorithm.
 When key agreement is used, the same length for the underlying block
 algorithm MUST be used.  If the content-encryption algorithm is
 AES-128 in CBC mode, then the key-wrap algorithm MUST be AES-128 Key
 Wrap [RFC3394].  If the content-encryption algorithm is AES-256 in
 CBC mode, then the key-wrap algorithm MUST be AES-256 Key Wrap
 [RFC3394].

4. EncryptedData

 If an implementation supports EncryptedData, then it MUST implement
 AES-128 in CBC mode [AES] and SHOULD implement AES-256 in CBC mode
 [AES].
 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].

Turner Standards Track [Page 3] RFC 7192 Algs for CMS Key Package Rcpt Content Type April 2014

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 the P-256 curve [RFC6090].

7. Security Considerations

 The security considerations from [RFC3370], [RFC3394], [RFC3560],
 [RFC4056], [RFC5084], [RFC5652], [RFC5753], and [RFC5754] apply.
 [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. Acknowledgements

 I'd like to thank Russ Housley for his early feedback on this
 document.

9. References

9.1. Normative References

 [AES]      National Institute of Standards and Technology, FIPS Pub
            197: Advanced Encryption Standard (AES), 26 November 2001.
 [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.
 [RFC3394]  Schaad, J. and R. Housley, "Advanced Encryption Standard
            (AES) Key Wrap Algorithm", RFC 3394, September 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.

Turner Standards Track [Page 4] RFC 7192 Algs for CMS Key Package Rcpt Content Type April 2014

 [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.
 [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.
 [RFC6090]  McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic
            Curve Cryptography Algorithms", RFC 6090, February 2011.
 [RFC7191]  Housley, R., "Cryptographic Message Syntax (CMS) Key
            Package Receipt and Error Content Types", RFC 7191, April
            2014.

9. Informative References

 [RFC5959]  Turner, S., "Algorithms for Asymmetric Key Package Content
            Type", RFC 5959, August 2010.
 [RFC6033]  Turner, S., "Algorithms for Cryptographic Message Syntax
            (CMS) Encrypted Key Package Content Type", RFC 6033,
            December 2010.
 [RFC6160]  Turner, S., "Algorithms for Cryptographic Message Syntax
            (CMS) Protection of Symmetric Key Package Content Types",
            RFC 6160, April 2011.
 [RFC6161]  Turner, S., "Elliptic Curve Algorithms for Cryptographic
            Message Syntax (CMS) Encrypted Key Package Content Type",
            RFC 6161, April 2011.

Turner Standards Track [Page 5] RFC 7192 Algs for CMS Key Package Rcpt Content Type April 2014

 [RFC6162]  Turner, S., "Elliptic Curve Algorithms for Cryptographic
            Message Syntax (CMS) Asymmetric Key Package Content Type",
            RFC 6162, April 2011.
 [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 6]

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