Pre-Shared Key Cipher Suites for TLS with SHA-256/384 and AES Galois Counter Mode
draft-ietf-tls-psk-new-mac-aes-gcm-05

TLS Working Group                                         Mohamad Badra 
Internet Draft                                         LIMOS Laboratory 
Intended status: Standards Track                       October 31, 2008 
Expires: April 2009                 
 
                                      
   Pre-Shared Key Cipher Suites for Transport Layer Security (TLS) with 
                  SHA-256/384 and AES Galois Counter Mode  
                 draft-ietf-tls-psk-new-mac-aes-gcm-05.txt 

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Copyright Notice 

   Copyright (C) The IETF Trust (2008). 

Abstract 

   RFC 4279 and RFC 4785 describe pre-shared key cipher suites for 
   Transport Layer Security (TLS).  However, all those cipher suites 
   use SHA-1 as their MAC algorithm.  This document describes a set of 
   pre-shared key cipher suites for TLS which uses stronger digest 
   algorithms (i.e., SHA-256 or SHA-384) and another set which uses the 
   Advanced Encryption Standard (AES) in Galois Counter Mode (GCM). 
 
 
 
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Table of Contents 

    
   1. Introduction...................................................3 
      1.1. Applicability Statement...................................3 
      1.2. Conventions used in this document.........................4 
   2. PSK, DHE_PSK and RSA_PSK Key Exchange Algorithms with AES-GCM..4 
   3. PSK, DHE_PSK and RSA_PSK Key Exchange with SHA-256/384.........4 
      3.1. PSK Key Exchange Algorithm with SHA-256/384...............5 
      3.2. DHE_PSK Key Exchange Algorithm with SHA-256/384...........5 
      3.3. RSA_PSK Key Exchange Algorithm with SHA-256/384...........5 
   4. Security Considerations........................................6 
   5. IANA Considerations............................................6 
   6. Acknowledgments................................................7 
   7. References.....................................................7 
      7.1. Normative References......................................7 
      7.2. Informative References....................................8 
   Author's Addresses................................................8 
   Intellectual Property Statement...................................8 
   Disclaimer of Validity............................................9 
    

 
 
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1. Introduction 

   The benefits of pre-shared symmetric-key vs. public-/private-key 
   pair based authentication for the key exchange in TLS have been 
   explained in the Introduction of [RFC4279].  This document leverages 
   the already defined algorithms for the application of newer, 
   generally regarded stronger, cryptographic primitives and building 
   blocks. 

   TLS 1.2 [RFC5246] adds support for authenticated encryption with 
   additional data (AEAD) cipher modes [RFC5116]. This document 
   describes the use of Advanced Encryption Standard (AES) [AES] in 
   Galois Counter Mode (GCM) [GCM] (AES-GCM) with various pre-shared 
   key (PSK) authenticated key exchange mechanisms ([RFC4279] and 
   [RFC4785]) in cipher suites for Transport Layer Security (TLS).  

   This document also specifies PSK cipher suites for TLS which replace 
   SHA-1 by SHA-256 or SHA-384 [SHS].  RFC 4279 [RFC4279] and RFC 4785 
   [RFC4785] describe PSK cipher suites for TLS.  However, all of the 
   RFC 4279 and the RFC 4785 cipher suites use HMAC-SHA1 as their MAC 
   algorithm.  Due to recent analytic work on SHA-1 [Wang05], the IETF 
   is gradually moving away from SHA-1 and towards stronger hash 
   algorithms. 

   Related TLS cipher suites with key exchange algorithms that are 
   authenticated using public/private key pairs have recently been 
   specified: 

      - RSA, DSS, and Diffie-Hellman based cipher suites in [RFC5288],  
        and 

      - ECC based cipher suites with SHA-256/384 and AES-GCM in  
        [RFC5289]. 

   The reader is expected to become familiar with these two memos prior 
   to studying this document. 

1.1. Applicability Statement  

   The cipher suites defined in Section 3 can be negotiated, whatever 
   the negotiated TLS version is. 

   The cipher suites defined in Section 2 can be negotiated in TLS 
   version 1.2 or higher. 

 
 
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1.2. Conventions used in this document  

   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. PSK, DHE_PSK and RSA_PSK Key Exchange Algorithms with AES-GCM 

   The following six cipher suites use the new authenticated encryption 
   modes defined in TLS 1.2 with AES in Galois Counter Mode (GCM) 
   [GCM].  The cipher suites with DHE_PSK key exchange algorithm 
   (TLS_DHE_PSK_WITH_AES_128_GCM_SHA256 and 
   TLS_DHE_PSK_WITH_AES_256_GCM_SHA348) provide Perfect Forward Secrecy 
   (PFS). 

      CipherSuite TLS_PSK_WITH_AES_128_GCM_SHA256        = {0xXX,0xXX}; 
      CipherSuite TLS_PSK_WITH_AES_256_GCM_SHA384        = {0xXX,0xXX}; 
      CipherSuite TLS_DHE_PSK_WITH_AES_128_GCM_SHA256    = {0xXX,0xXX}; 
      CipherSuite TLS_DHE_PSK_WITH_AES_256_GCM_SHA384    = {0xXX,0xXX}; 
      CipherSuite TLS_RSA_PSK_WITH_AES_128_GCM_SHA256    = {0xXX,0xXX}; 
      CipherSuite TLS_RSA_PSK_WITH_AES_256_GCM_SHA384    = {0xXX,0xXX}; 

   These cipher suites use authenticated encryption with additional 
   data (AEAD) algorithms AEAD_AES_128_GCM and AEAD_AES_256_GCM as 
   described in RFC 5116.  GCM is used as described in [RFC5288]. 

   The PSK, DHE_PSK and RSA_PSK key exchanges are performed as defined 
   in [RFC4279]. 

   The Pseudo Random Function (PRF) algorithms SHALL be as follows: 

       For cipher suites ending with _SHA256, the PRF is the TLS PRF  
       [RFC5246] with SHA-256 as the hash function. 

       For cipher suites ending with _SHA384, the PRF is the TLS PRF  
       [RFC5246] with SHA-384 as the hash function. 

   Implementations MUST send a TLS Alert 'bad_record_mac' for all types 
   of failures encountered in processing the AES-GCM algorithm. 

3. PSK, DHE_PSK and RSA_PSK Key Exchange with SHA-256/384 

   The first two cipher suites described in each of the following three 
   sections use AES [AES] in Cipher Block Chaining (CBC) mode [CBC] for 
   data confidentiality, whereas the other two cipher suites do not 
   provide data confidentiality; all cipher suites provide integrity 
   protection and authentication using HMAC-based MACs. 
 
 
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3.1. PSK Key Exchange Algorithm with SHA-256/384 

      CipherSuite TLS_PSK_WITH_AES_128_CBC_SHA256        = {0xXX,0xXX}; 
      CipherSuite TLS_PSK_WITH_AES_256_CBC_SHA384        = {0xXX,0xXX}; 
      CipherSuite TLS_PSK_WITH_NULL_SHA256               = {0xXX,0xXX};  
      CipherSuite TLS_PSK_WITH_NULL_SHA384               = {0xXX,0xXX}; 

   The above four cipher suites are the same as the corresponding 
   cipher suites in RFC 4279 and RFC 4785 (with names ending in "_SHA" 
   in place of "_SHA256" or "_SHA384"), except for the hash and PRF 
   algorithms: 

        o  For cipher suites with names ending in "_SHA256": 

           -  The MAC is HMAC [RFC2104] with SHA-256 as the hash  
              function. 

           -  When negotiated in a version of TLS prior to 1.2, the PRF  
              from that version is used; otherwise the PRF is the TLS  
              PRF [RFC5246] with SHA-256 as the hash function. 

        o  For cipher suites with names ending in "_SHA384": 

           -  The MAC is HMAC [RFC2104] with SHA-384 as the hash  
              function. 

           -  When negotiated in a version of TLS prior to 1.2, the PRF  
              from that version is used; otherwise the PRF is the TLS  
              PRF [RFC5246] with SHA-384 as the hash function. 

3.2. DHE_PSK Key Exchange Algorithm with SHA-256/384 

      CipherSuite TLS_DHE_PSK_WITH_AES_128_CBC_SHA256    = {0xXX,0xXX};   
      CipherSuite TLS_DHE_PSK_WITH_AES_256_CBC_SHA384    = {0xXX,0xXX}; 
      CipherSuite TLS_DHE_PSK_WITH_NULL_SHA256           = {0xXX,0xXX};     
      CipherSuite TLS_DHE_PSK_WITH_NULL_SHA384           = {0xXX,0xXX}; 

   The above four cipher suites are the same as the corresponding 
   cipher suites in RFC 4279 and RFC 4785 (with names ending in "_SHA" 
   in place of "_SHA256" or "_SHA384"), except for the hash and PRF 
   algorithms, as explained in Section 3.1. 

3.3. RSA_PSK Key Exchange Algorithm with SHA-256/384 

      CipherSuite TLS_RSA_PSK_WITH_AES_128_CBC_SHA256    = {0xXX,0xXX}; 
      CipherSuite TLS_RSA_PSK_WITH_AES_256_CBC_SHA384    = {0xXX,0xXX}; 

 
 
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      CipherSuite TLS_RSA_PSK_WITH_NULL_SHA256           = {0xXX,0xXX}; 
      CipherSuite TLS_RSA_PSK_WITH_NULL_SHA384           = {0xXX,0xXX}; 

   The above four cipher suites are the same as the corresponding 
   cipher suites in RFC 4279 and RFC 4785 (with names ending in "_SHA" 
   in place of "_SHA256" or "_SHA384"), except for the hash and PRF 
   algorithms, as explained in Section 3.1. 

4. Security Considerations 

   The security considerations in [RFC4279], [RFC4785] and [RFC5288] 
   apply to this document as well.  In particular, as authentication-
   only cipher suites (with no encryption) defined here do not support 
   confidentiality, care should be taken not to send sensitive 
   information (such as passwords) over connections protected with one 
   of the cipher suites with NULL encryption defined in this document. 

   As described in [RFC5288], the cipher suites defined in the Section 
   2 of this document may only be used with TLS 1.2 or greater. The 
   cipher suites defined in the Section 3 may be used, whatever the 
   negotiated TLS version is. 

5. IANA Considerations 

   IANA has assigned the following values for the cipher suites defined 
   in this document: 

      CipherSuite TLS_PSK_WITH_AES_128_GCM_SHA256        = {0xXX,0xXX}; 
      CipherSuite TLS_PSK_WITH_AES_256_GCM_SHA384        = {0xXX,0xXX}; 
      CipherSuite TLS_DHE_PSK_WITH_AES_128_GCM_SHA256    = {0xXX,0xXX}; 
      CipherSuite TLS_DHE_PSK_WITH_AES_256_GCM_SHA384    = {0xXX,0xXX}; 
      CipherSuite TLS_RSA_PSK_WITH_AES_128_GCM_SHA256    = {0xXX,0xXX}; 
      CipherSuite TLS_RSA_PSK_WITH_AES_256_GCM_SHA384    = {0xXX,0xXX};    
      CipherSuite TLS_PSK_WITH_AES_128_CBC_SHA256        = {0xXX,0xXX}; 
      CipherSuite TLS_PSK_WITH_AES_256_CBC_SHA384        = {0xXX,0xXX}; 
      CipherSuite TLS_PSK_WITH_NULL_SHA256               = {0xXX,0xXX}; 
      CipherSuite TLS_PSK_WITH_NULL_SHA384               = {0xXX,0xXX}; 
      CipherSuite TLS_DHE_PSK_WITH_AES_128_CBC_SHA256    = {0xXX,0xXX};   
      CipherSuite TLS_DHE_PSK_WITH_AES_256_CBC_SHA384    = {0xXX,0xXX}; 
      CipherSuite TLS_DHE_PSK_WITH_NULL_SHA256           = {0xXX,0xXX};     
      CipherSuite TLS_DHE_PSK_WITH_NULL_SHA384           = {0xXX,0xXX}; 
      CipherSuite TLS_RSA_PSK_WITH_AES_128_CBC_SHA256    = {0xXX,0xXX}; 
      CipherSuite TLS_RSA_PSK_WITH_AES_256_CBC_SHA384    = {0xXX,0xXX}; 
      CipherSuite TLS_RSA_PSK_WITH_NULL_SHA256           = {0xXX,0xXX}; 
      CipherSuite TLS_RSA_PSK_WITH_NULL_SHA384           = {0xXX,0xXX}; 

 
 
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6. Acknowledgments 

   This draft borrows heavily from [RFC5289] and [RFC5288]. 

   The author appreciates Alfred Hoenes for his detailed review and 
   effort on issues resolving discussion.  The author would like also 
   to acknowledge Ibrahim Hajjeh, Simon Josefsson, Hassnaa Moustafa, 
   Joseph Salowey and Pascal Urien for their reviews of the content of 
   the document. 

7. References 

7.1. Normative References 

   [AES]     National Institute of Standards and Technology, 
             "Specification for the Advanced Encryption Standard 
             (AES)", FIPS 197, November 2001. 

   [CBC]     National Institute of Standards and Technology, 
             "Recommendation for Block Cipher Modes of Operation - 
             Methods and Techniques", SP 800-38A, December 2001. 

   [GCM]     National Institute of Standards and Technology, 
             "Recommendation for Block Cipher Modes of Operation: 
             Galois/Counter Mode (GCM) for Confidentiality and 
             Authentication", SP 800-38D, November 2007. 

   [SHS]     National Institute of Standards and Technology, "Secure 
             Hash Standard", FIPS 180-2, August 2002. 

   [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
             Hashing for Message Authentication", RFC 2104, February 
             1997. 

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 
             Requirement Levels", BCP 14, RFC 2119, March 1997. 

   [RFC4279] Eronen, P. and H. Tschofenig, "Pre-Shared Key Ciphersuites 
             for Transport Layer Security (TLS)", RFC 4279, December 
             2005. 

   [RFC4785] Blumenthal, U., Goel, P., "Pre-Shared Key (PSK) 
             Ciphersuites with NULL Encryption for Transport Layer 
             Security (TLS)", RFC 4785, January 2007. 

   [RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated 
             Encryption", RFC 5116, January 2008.  
 
 
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   [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 
             (TLS) Protocol Version 1.2", RFC 5246, August 2008. 

   [RFC5288] Salowey, J., A. Choudhury, and C. McGrew, "RSA based AES-
             GCM Cipher Suites for TLS", RFC 5288, August 2008. 

7.2. Informative References 

   [RFC5289] Rescorla, E., "TLS Elliptic Curve Cipher Suites with SHA-
             256/384 and AES Galois Counter Mode", RFC 5289, August 
             2008. 

   [Wang05]  Wang, X., Yin, Y., and H. Yu, "Finding Collisions in the 
             Full SHA-1", CRYPTO 2005, August 2005. 

Author's Addresses 

   Mohamad Badra 
   LIMOS Laboratory - UMR6158, CNRS 
   France 

   Email: badra@isima.fr 

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Disclaimer of Validity 

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Copyright Statement 

   Copyright (C) The IETF Trust (2008). 

   This document is subject to the rights, licenses and restrictions 
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Acknowledgment 

   Funding for the RFC Editor function is currently provided by the 
   Internet Society. 

 
 
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