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Versions: 00 01 02 03 04 05 06 RFC 6668

Network Working Group                                           d. bider
Internet-Draft                                           Bitvise Limited
Updates: 4253 (if approved)                                   M. Baushke
Intended status: Standards Track                  Juniper Networks, Inc.
Expires: May 17, 2012                                  November 14, 2011

 SHA-2 Data Integrity Verification for the Secure Shell (SSH) Transport
                             Layer Protocol


   This memo defines algorithm names and parameters for use of some of
   the SHA-2 family of secure hash algorithms for data integrity
   verification in the Secure Shell (SSH) protocol.

   This document adds new Message Authentication Code (MAC) algorithms
   to the set defined in RFC 4253 [RFC4253].

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 17, 2012.

Copyright Notice

   Copyright (c) 2011 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

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Internet-Draft              SHA-2 MAC for SSH              November 2011

   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.  Overview and Rationale

   SSH [RFC4251] is a very common protocol for secure remote login on
   the Internet.  Currently, SSH defines data integrity verification
   using SHA-1 and MD5 algorithms [RFC4253].  Due to recent security
   concerns with these two algorithms [RFC6151][RFC6194], implementors
   and users request support for data integrity verification using some
   of the SHA-2 family of of secure hash algorithms.

   Please send comments on this draft to ietf-ssh@NetBSD.org.

1.1.  Requirements Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

2.  Data Integrity Algorithms

   This memo adopts the style and conventions of [RFC4253] in defining
   new data integrity algorithms.

   The following new data integrity algorithms are defined:

   hmac-sha2-256     RECOMMENDED   HMAC-SHA2-256
                                   (digest length = 32 bytes,
                                    key length    = 32 bytes)

   hmac-sha2-256-96  OPTIONAL      first 96 bits of HMAC-SHA2-256
                                   (digest length = 12 bytes,
                                    key length    = 32 bytes)

   hmac-sha2-512     OPTIONAL      HMAC-SHA2-512
                                   (digest length = 64 bytes,
                                    key length    = 64 bytes)

   hmac-sha2-512-96  OPTIONAL      first 96 bits of HMAC-SHA2-512
                                   (digest length = 12 bytes,
                                    key length    = 64 bytes)

                                 Figure 1

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Internet-Draft              SHA-2 MAC for SSH              November 2011

   The HMAC mechanism is defined in [RFC2104].

   The SHA-2 family of secure hash algorithms are defined in

   Sample code for the SHA-based HMAC algorithms are available in
   [RFC6234].  The variants HMAC-SHA2-224 and HMAC-SHA2-384 algorithms
   were considered, but not added to this list as they have the same
   computational requirements of HMAC-SHA2-256 and HMAC-SHA2-512
   respectively and do not seem to be much used in practice.

   Test vectors for use of HMAC with SHA-2 are provided in [RFC4231].

   Users, implementors, and administrators may choose to put these new
   Macs into the proposal ahead of the REQUIRED hmac-sha1 algorithm
   defined in [RFC4253] so that they would be negotiated first.

3.  IANA Considerations

   This document augments the MAC Algorithm Names in [RFC4253] and

   IANA is requested to update the SSH algorithm registry with the
   following entries:

   MAC Algorithm Name      Reference       Note
   hmac-sha2-256           This draft      Section 2
   hmac-sha2-256-96        This draft      Section 2
   hmac-sha2-512           This draft      Section 2
   hmac-sha2-512-96        This draft      Section 2

                                 Figure 2

4.  Security Considerations

   The security considerations of RFC 4253 [RFC4253] apply to this

   The current attacks on HMAC-SHA1 do not yet seem to indicate a
   practical vulnerability when used as a message authentication code.
   National Institute of Standards and Technology (NIST) publications:
   NIST Special Publication (SP) 800-107 [800-107] and NIST SP 800-131
   [800-131] suggest that HMAC-SHA1 and HMAC-SHA2-256 have a security
   strength of 128 bits and 256 bits respectively.

   Even so, many users seem to be interested in the perceived safety of

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   using a stronger algorithm than HMAC-SHA1.

5.  References

5.1.  Normative References

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

   [RFC4231]  Nystrom, M., "Identifiers and Test Vectors for HMAC-SHA-
              224, HMAC-SHA-256, HMAC-SHA-384, and HMAC-SHA-512",
              RFC 4231, December 2005.

   [RFC4253]  Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
              Transport Layer Protocol", RFC 4253, January 2006.

5.2.  Informative References

              National Institute of Standards and Technology (NIST),
              "Secure Hash Standard (SHS)", FIPS PUB 180-3,
              October 2008.

   [800-107]  National Institute of Standards and Technology (NIST),
              "Recommendation for Applications Using Approved Hash
              Algorithms", NIST Special Publication 800-107,
              February 2009.

   [800-131]  National Institute of Standards and Technology (NIST),
              "Recommendation for the Transitioning of Cryptographic
              Algorithms and Key Sizes", DRAFT NIST Special
              Publication 800-131, January 2010.

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

   [RFC4250]  Lehtinen, S. and C. Lonvick, "SSH Protocol Assigned
              Numbers", RFC 4250, January 2006.

   [RFC4251]  Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
              Protocol Architecture", RFC 4251, January 2006.

   [RFC6151]  Turner, S. and L. Chen, "Updated Security Considerations
              for the MD5 Message-Digest and the HMAC-MD5 Algorithms",
              RFC 6151, March 2011.

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Internet-Draft              SHA-2 MAC for SSH              November 2011

   [RFC6194]  Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security
              Considerations for the SHA-0 and SHA-1 Message-Digest
              Algorithms", RFC 6194, March 2011.

   [RFC6234]  Eastlake, D. and T. Hansen, "US Secure Hash Algorithms
              (SHA and SHA-based HMAC and HKDF)", RFC 6234, May 2011.

Authors' Addresses

   denis bider
   Bitvise Limited
   Suites 41/42, Victoria House
   26 Main Street

   Phone: +1 869 762 1410
   Email: ietf-ssh2@denisbider.com
   URI:   http://www.bitvise.com/

   Mark D. Baushke
   Juniper Networks, Inc.
   1194 N Mathilda Av
   Sunnyvale, CA  94089-1206

   Phone: +1 408 745 2952
   Email: mdb@juniper.net
   URI:   http://www.juniper.net/

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