More Modular Exponential (MODP) Diffie-Hellman Key Exchange Groups for Secure Shell (SSH)

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Last updated 2016-02-15
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, 4419, 4432, 4462, 5656                  February 15, 2016
         (if approved)
Intended status: Standards Track
Expires: August 18, 2016

 More Modular Exponential (MODP) Diffie-Hellman Key Exchange Groups for
                           Secure Shell (SSH)


   This document defines two added Modular Exponential (MODP) Groups for
   the Secure Shell (SSH) protocol.  It also updates [RFC4253],
   [RFC4419], [RFC4462], and [RFC5656] by specifying the set key
   exchange algorithms that currently exist and which ones MUST, SHOULD,
   MAY, and SHOULD NOT be implemented including two new Diffie-Hellman
   key exchange algorithms using SHA-2 hashes.

Status of This Memo

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   This Internet-Draft will expire on August 18, 2016.

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   to this document.  Code Components extracted from this document must
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   described in the Simplified BSD License.

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] implementer 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.

   The United States Information Assurance Directorate at the National
   Security Agency has published a FAQ [MFQ-U-OO-815099-15] suggesting
   that the use of ECDH using the nistp256 curve and SHA-2 based hashes
   less than SHA2-384 are no longer sufficient for transport of Top
   Secret information.  It is for this reason that this draft moves
   ecdh-sha2-nistp256 from a REQUIRED to OPTIONAL as a key exchange
   method.  This is the same reason that the stronger MODP groups being
   introduced are using SHA2-512 as the hash algorithm.  Group14 is
   already present in most SSH implementations and most implementations
   already have a SHA2-256 implementation, so diffie-hellman-
   group14-sha256 is provided as an easy to implement and faster to use
   key exchange for small embedded applications.

   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.

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   The following new key exchange algorithms are defined:

   Key Exchange Method Name          Note
   diffie-hellman-group14-sha256     MAY/OPTIONAL
   diffie-hellman-group16-sha512     SHOULD/RECOMMENDED
   diffie-hellman-group18-sha512     MAY/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"
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