


Network Working Group                                          M. Salter
Internet-Draft                                  National Security Agency
Intended status:  Informational                              E. Rescorla
Expires:  December 4, 2007                             Network Resonance
                                                            June 2, 2007


                     Suite B Cipher Suites for TLS
                    draft-rescorla-tls-suiteb-01.txt

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Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   The United States Government has published guidelines for "NSA Suite
   B Cryptography" dated July, 2005, which defines cryptographic
   algorithm polcy for national security applications.  This document
   defines a profile of TLS which is conformant with Suite B.






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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Conventions Used In This Document . . . . . . . . . . . . . . . 3
   3.  Suite B Requirements  . . . . . . . . . . . . . . . . . . . . . 3
   4.  Suite B Compliance Requirements . . . . . . . . . . . . . . . . 4
     4.1.  Security Levels . . . . . . . . . . . . . . . . . . . . . . 4
     4.2.  Acceptable Curves . . . . . . . . . . . . . . . . . . . . . 5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 6
   Intellectual Property and Copyright Statements  . . . . . . . . . . 8



































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1.  Introduction

   In July, 2005 the National Security Agency posted "Fact Sheet, NSA
   Suite B Cryptography" which stated:

       To complement the existing policy for the use of the Advanced
       Encryption Standard (AES) to protect national security systems
       and information as specified in The National Policy on the use of
       the Advanced Encryption Standard (AES) to Protect National
       Security Systems and National Security Information (CNSSP-15),
       the National Security Agency (NSA) announced Suite B Cryptography
       at the 2005 RSA Conference.  In addition to the AES, Suite B
       includes cryptographic algorithms for hashing, digital
       signatures, and key exchange.

       Suite B only specifies the cryptographic algorithms to be
       used. Many other factors need to be addressed in determining
       whether a particular device implementing a particular set of
       cryptographic algorithms should be used to satisfy a particular
       requirement.

   Among those factors are "requirements for interoperability both
   domestically and internationally".

   This document is a profile of of TLS 1.2 [I-D.ietf-tls-rfc4346-bis]
   and of the cipher suites defined in [I-D.ietf-tls-ecc-new-mac], but
   does not itself define any new cipher suites.  This profile requires
   TLS 1.2.


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].


3.  Suite B Requirements

   The "Suite B Fact Sheet" requires that key establishment and
   authentication algorithms be based on Elliptic Curve Cryptography,
   that the encryption algorithm be AES [AES], and that the function
   used for key derivation and data integrity be SHA [SHS].  It defines
   two security levels, of 128 and 192 bits.

   In particular it states:





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      SUITE B includes:

       Encryption:          Advanced Encryption Standard (AES)  -
                            FIPS 197 (with keys sizes of 128 and 256
                            bits)

       Digital Signature:   Elliptic Curve Digital Signature Algorithm -
                            FIPS 186-2 (using the curves with 256 and
                            384-bit prime moduli)

       Key Exchange:        Elliptic Curve Diffie-Hellman or Elliptic
                            Curve MQV Draft NIST Special Publication
                            800-56 (using the curves with 256 and
                            384-bit prime moduli)

       Hashing:             Secure Hash Algorithm - FIPS 180-2
                            (using SHA-256 and SHA-384)

      All implementations of Suite B must, at a minimum, include AES
      with 128-bit keys, the 256-bit prime modulus elliptic curve and
      SHA-256 as a common mode for widespread interoperability.

   The 128-bit security level corresponds to an elliptic curve size of
   256 bits, AES-128, and SHA-256.  The 192-bit security level
   corresponds to an elliptic curve size of 384 bits, AES-256, and SHA-
   384.


4.  Suite B Compliance Requirements

   To be considered "Suite B compatible" at least one of the Galois
   Counter Mode (GCM) CipherSuites defined in [I-D.ietf-tls-ecc-new-mac]
   MUST be negotiated.  In compliance with the guidance in the Suite B
   Fact Sheet every TLS implementation of Suite B SHOULD implement
   TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256.

4.1.  Security Levels

   As described in Section 1, Suite B specifies two security levels, 128
   and 192 bit.  The following table lists the security levels for each
   cipher suite:










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       +-----------------------------------------+----------------+
       | Cipher Suite                            | Security Level |
       +-----------------------------------------+----------------+
       | TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 | 128            |
       | TLS_ECDH_ECDSA_WITH_AES_128_GCM_SHA256  | 128            |
       | TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 | 192            |
       | TLS_ECDH_ECDSA_WITH_AES_256_GCM_SHA384  | 192            |
       +-----------------------------------------+----------------+

4.2.  Acceptable Curves

   RFC 4492 defines a variety of elliptic curves.  For cipher suites
   defined in this specification, only secp256r1 (23) or secp384r1 (24)
   may be used.  (These are the same curves that appear in FIPS 186-2 as
   P-256 and P-384, respectively.)  For cipher suites at the 128-bit
   security level, secp256r1 MUST be used.  For cipher suites at the
   192-bit security level, secp384r1 MUST be used.  RFC 4492 requires
   that uncompressed (0) form be supported. ansiX962_compressed_prime(1)
   point formats MAY be supported.

   Clients desiring to negotiate only a Suite B-compliant connection
   MUST generate a "Supported Elliptic Curves Extension" containing only
   the allowed curves.  These curves MUST match the cipher suite
   security levels being offered.  Clients which are willing to do both
   Suite B-compliant and non-Suite B-compliant connections MAY omit the
   extension or send the extension but offer other curves as well as the
   appropriate Suite B ones.

   Servers desiring to negotiate a Suite B-compliant connection SHOULD
   check for the presence of the extension, but MUST NOT negotiate
   inappropriate curves even if they are offered by the client.  This
   allows a Client which is willing to do either Suite B-compliant or
   non-Suite B-compliant modes to interoperate with a server which will
   only do Suite B-compliant modes.  If the client does not advertise an
   acceptable curve, the server MUST generate a fatal
   "handshake_failure" alert and terminate the connection.  Clients MUST
   check the chosen curve to make sure it is acceptable.


5.  Security Considerations

   Most of the security considerations for this document are described
   in TLS 1.2 [I-D.ietf-tls-rfc4346-bis], RFC 4492 [RFC4492], and
   [I-D.ietf-tls-ecc-new-mac].  Readers should consult those documents.

   In order to meet the goal of a consistent security level for the
   entire cipher suite, in Suite B mode TLS implementations MUST ONLY
   use the curves defined in Section 4.2.  Otherwise, it is possible to



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   have a set of symmetric algorithms with much weaker or stronger
   security properties than the asymmetric (ECC) algorithms.


6.  IANA Considerations

   This document defines no actions for IANA.


7.  Acknowledgements

   This work was supported by the US Department of Defense.


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.

   [RFC4492]  Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
              Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
              for Transport Layer Security (TLS)", RFC 4492, May 2006.

   [I-D.ietf-tls-rfc4346-bis]
              Dierks, T. and E. Rescorla, "The TLS Protocol Version
              1.2", draft-ietf-tls-rfc4346-bis-03 (work in progress),
              March 2007.

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

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

   [I-D.ietf-tls-ecc-new-mac]
              Rescorla, E., "TLS Elliptic Curve Cipher Suites with SHA-
              256/384 and AES Galois Counter Mode", April 2007.

8.2.  Informative References









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Authors' Addresses

   Margaret Salter
   National Security Agency
   9800 Savage Rd.
   Fort Meade  20755-6709
   USA

   Email:  msalter@restarea.ncsc.mil


   Eric Rescorla
   Network Resonance
   2483 E. Bayshore #212
   Palo Alto  94303
   USA

   Email:  ekr@networkresonance.com

































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Acknowledgment

   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).





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