More Modular Exponential (MODP) Diffie-Hellman Groups for SSH

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Last updated 2015-12-10
Replaced by draft-ietf-curdle-ssh-kex-sha2
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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


   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

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   This Internet-Draft will expire on June 12, 2016.

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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 SHA1 [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

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   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

   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.

Baushke                   Expires June 12, 2016                 [Page 2]
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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

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
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