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More Modular Exponential (MODP) Diffie-Hellman Groups for SSH
draft-baushke-ssh-dh-group-sha2-01

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Document Type
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
Author Mark D. Baushke
Last updated 2015-12-10
Replaced by draft-ietf-curdle-ssh-kex-sha2, draft-ietf-curdle-ssh-kex-sha2, RFC 9142
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draft-baushke-ssh-dh-group-sha2-01
Internet Engineering Task Force                               M. Baushke
Internet-Draft                                    Juniper Networks, Inc.
Updates: 4253 (if approved)                            December 10, 2015
Intended status: Standards Track
Expires: June 12, 2016

     More Modular Exponential (MODP) Diffie-Hellman Groups for SSH
                   draft-baushke-ssh-dh-group-sha2-01

Abstract

   This document defines two added Modular Exponential (MODP) Groups for
   the Secure Shell (SSH) protocol.  It also updates [RFC4253] by
   specifying new RECOMMENDED and new OPTIONAL Diffie-Hellman key
   exchange algorithms using SHA-2 hashes.

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 June 12, 2016.

Copyright Notice

   Copyright (c) 2015 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.

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1.  Overview and Rationale

   Secure Shell (SSH) is a common protocol for secure communication on
   the Internet.  In [RFC4253], SSH originally defined the Key Exchange
   Method Name diffie-hellman-group1-sha1 which used [RFC2409] Oakley
   Group 1 (a MODP group with 768 bits) and SHA-1 [RFC3174].  Due to
   recent security concerns with SHA-1 [RFC6194] and with MODP groups
   with less than 2048 bits [NIST-SP-800-131Ar1] implementors and users
   request support for larger MODP group sizes with data integrity
   verification using the SHA-2 family of secure hash algorithms as well
   as MODP groups providing more security.

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

2.  Requirements Language

   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.  Key Exchange Algorithms

   This memo adopts the style and conventions of [RFC4253] in specifying
   how the use of new data key exchange is indicated in SSH.

   The following new key exchange algorithms are defined:

   Key Exchange Method Name          Note
   diffie-hellman-group1-sha1        NOT RECOMMENDED
   diffie-hellman-group14-sha256     RECOMMENDED
   diffie-hellman-group15-sha256     RECOMMENDED
   diffie-hellman-group16-sha256     OPTIONAL

                                 Figure 1

   The SHA-2 family of secure hash algorithms are defined in
   [FIPS-180-4].

   The method of key exchange used for the name "diffie-hellman-
   group14-sha256" is the same as that for "diffie-hellman-group14-sha1"
   escept that the SHA2-256 hash algorith is used.

   The group15 and group16 names are the same as those specified in
   [RFC3526] as 3072-bit MODP Group 14 and 4096-bit MODP Group 15.

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4.  IANA Considerations

   This document augments the Key Exchange Method Names in [RFC4253].

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

   Key Exchange Method Name       Reference   Note
   diffie-hellman-group1-sha1     RFC4253     NOT RECOMMENDED
   diffie-hellman-group14-sha256  This draft  RECOMMENDED
   diffie-hellman-group15-sha256  This draft  RECOMMENDED
   diffie-hellman-group16-sha256  This draft  OPTIONAL

                                 Figure 2

   It is RECOMMENDED that the new diffie-hellman-group14-sha256 method
   be proposed before the diffie-hellman-group14-sha1 method.

5.  Security Considerations

   The security considerations of [RFC4253] apply to this document.

   The security considerations of [RFC3526] suggest that these MODP
   groups have security strengths given in this table.

   Group modulus security strength estimates

   +--------+----------+---------------------+---------------------+
   | Group  | Modulus  | Strength Estimate 1 | Strength Estimate 2 |
   |        |          +----------+----------+----------+----------+
   |        |          |          | exponent |          | exponent |
   |        |          | in bits  | size     | in bits  | size     |
   +--------+----------+----------+----------+----------+----------+
   |  14    | 2048-bit |      110 |     220- |      160 |     320- |
   |  15    | 3072-bit |      130 |     260- |      210 |     420- |
   |  16    | 4096-bit |      150 |     300- |      240 |     480- |
   +--------+----------+---------------------+---------------------+

                                 Figure 3

   Many users seem to be interested in the perceived safety of using the
   SHA2-based algorithms for hashing.

6.  References

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6.1.  Normative References

   [FIPS-180-4]
              National Institute of Standards and Technology, "Secure
              Hash Standard (SHS)", FIPS PUB 180-4, August 2015,
              <http://nvlpubs.nist.gov/nistpubs/FIPS/
              NIST.FIPS.180-4.pdf>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3526]  Kivinen, T. and M. Kojo, "More Modular Exponential (MODP)
              Diffie-Hellman groups for Internet Key Exchange (IKE)",
              RFC 3526, DOI 10.17487/RFC3526, May 2003,
              <http://www.rfc-editor.org/info/rfc3526>.

   [RFC4253]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253,
              January 2006, <http://www.rfc-editor.org/info/rfc4253>.

6.2.  Informative References

   [NIST-SP-800-131Ar1]
              Barker, and Roginsky, "Transitions: Recommendation for the
              Transitioning of the Use of Cryptographic Algorithms and
              Key Lengths", NIST Special Publication 800-131A Revision
              1, November 2015,
              <http://nvlpubs.nist.gov/nistpubs/SpecialPublications/
              NIST.SP.800-131Ar1.pdf>.

   [RFC2409]  Harkins, D. and D. Carrel, "The Internet Key Exchange
              (IKE)", RFC 2409, DOI 10.17487/RFC2409, November 1998,
              <http://www.rfc-editor.org/info/rfc2409>.

   [RFC3174]  Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm 1
              (SHA1)", RFC 3174, DOI 10.17487/RFC3174, September 2001,
              <http://www.rfc-editor.org/info/rfc3174>.

   [RFC6194]  Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security
              Considerations for the SHA-0 and SHA-1 Message-Digest
              Algorithms", RFC 6194, DOI 10.17487/RFC6194, March 2011,
              <http://www.rfc-editor.org/info/rfc6194>.

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Author's Address

   Mark D.     Baushke
   Juniper Networks, Inc.
   1133 Innovation Way
   Sunnyvale, CA  94089-1228
   US

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

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