Network Working Group                                 Sean Turner, IECA 
Internet Draft                                              May 7, 2010 
Intended Status: Standard Track 
Expires: November 7, 2010 
 
 
                                      
             Algorithms for Cryptographic Message Syntax (CMS) 
                    Encrypted Key Package Content Type 
          draft-turner-encryptedkeypackagecontenttype-algs-02.txt 


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 Internet-Draft is submitted to IETF in full conformance with the 
   provisions of BCP 78 and BCP 79. 

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Copyright Notice 

   Copyright (c) 2010 IETF Trust and the persons identified as the 
   document authors. All rights reserved. 

 
 
 
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   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. 

1. Introduction 

   This document describes the conventions for using several 
   cryptographic algorithms with the Cryptographic Message Syntax (CMS) 
   encrypted key package content type [RFCTBD].  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-OAEP [RFC3560] SHOULD be supported. 

   When key agreement is used, Diffie-Hellman ephemeral-static [RFC3370] 
   MUST be supported. 

   Regardless of the key management technique choice, implementations 
   MUST support AES-128 Key Wrap with Padding [RFC5649].  
   Implementations SHOULD support AES-256 Key Wrap with Padding 
   [RFC5649]. 

 
 
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   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]. 

3. EncryptedData 

   EncryptedData [RFC5652] requires that keys be managed by other means; 
   therefore, the only algorithm specified is the content encryption 
   algorithm. 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-GCM [RFC5084] and SHOULD support 256-bit AES-GCM 
   [RFC5084].  Implementations MAY also support AES-CCM [RFC5084]. 

5. Public Key Sizes 

   The easiest way to implement the key transport requirement for 
   EnvelopedData and AuthEnvelopedData is with public key certificates 
   [RFC5280]. If an implementation supports RSA, RSAES-OAEP, or DH,
   then it MUST support key lengths from 1024-bit to 2048-bit,
   inclusive. 

6. Security Considerations 

   The security considerations from [RFC3370], [RFC3560], [RFC5083], 
   [RFC5084], [RFC5649], [RFC5652], and [RFCTBD] 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 
   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. 

 
 
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   [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.  

7. IANA Considerations 

   None.  Please remove this section prior to publication as an RFC. 

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 the Cryptographic Message Syntax (CMS)", RFC 
               3560, July 2003. 

   [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)", RFC 
               5652, September 2009. 

   [RFCTBD]    Turner, S., and R. Housley, "Cryptographic Message Syntax 
               (CMS) Encrypted Key Package Content Type", draft-turner-
               encryptedkeypackagecontenttype-02.txt, work-in-progress. 

 
 
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   /** 
   RFC Editor: Please replace "TBD" with the number of the published 
   RFC.  Please do this in both the references and the text. 
   **/ 

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.  

Authors' Addresses 

   Sean Turner 
   IECA, Inc. 
   3057 Nutley Street, Suite 106 
   Fairfax, VA 22031 
   USA 

   EMail: turners@ieca.com 



























 
 
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