More Modular Exponentiation (MODP) Diffie-Hellman (DH) Key Exchange (KEX) Groups for Secure Shell (SSH)
RFC 8268

Document Type RFC - Proposed Standard (December 2017; No errata)
Last updated 2017-12-13
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Internet Engineering Task Force (IETF)                        M. Baushke
Request for Comments: 8268                        Juniper Networks, Inc.
Updates: 4250, 4253                                        December 2017
Category: Standards Track
ISSN: 2070-1721

         More Modular Exponentiation (MODP) Diffie-Hellman (DH)
            Key Exchange (KEX) Groups for Secure Shell (SSH)

Abstract

   This document defines added Modular Exponentiation (MODP) groups for
   the Secure Shell (SSH) protocol using SHA-2 hashes.  This document
   updates RFC 4250.  This document updates RFC 4253 by correcting an
   error regarding checking the Peer's DH Public Key.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8268.

Copyright Notice

   Copyright (c) 2017 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
   (https://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.

Baushke                      Standards Track                    [Page 1]
RFC 8268             More MODP DH KEX Groups for SSH       December 2017

Table of Contents

   1.  Overview and Rationale  . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
   3.  Key Exchange Algorithms . . . . . . . . . . . . . . . . . . .   4
   4.  Checking the Peer's DH Public Key . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Overview and Rationale

   Secure Shell (SSH) is a common protocol for secure communication on
   the Internet.  Security protocols and primitives are an active area
   for research and help to suggest updates to SSH.

   Section 8 of [RFC4253] contains a small error in point 3 regarding
   checking the Peer's DH Public Key.  Section 4 of this document
   provides the correction.

   Due to security concerns with SHA-1 [RFC6194] and with MODP groups
   with less than 2048 bits [NIST-SP-800-131Ar1], implementers and users
   should request support for larger Diffie-Hellman (DH) MODP group
   sizes with data-integrity verification by using the SHA-2 family of
   secure hash algorithms and by having MODP groups provide more
   security.  The use of larger MODP groups and the move to the SHA-2
   family of hashes are important features to strengthen the key
   exchange algorithms available to the SSH client and server.

   DH primes being adopted by this document are all "safe primes" such
   that p = 2q + 1 where q is also a prime.  New MODP groups are being
   introduced starting with the MODP 3072-bit group15.  All use SHA512
   as the hash algorithm.

   The DH 2048-bit MODP group14 is already present in most SSH
   implementations and most implementations already have a SHA256
   implementation, so "diffie-hellman-group14-sha256" is provided as
   easy to implement.

   It is intended that these new MODP groups with SHA-2-based hashes
   update Section 6.4 of [RFC4253] and Section 4.10 of [RFC4250].

Baushke                      Standards Track                    [Page 2]
RFC 8268             More MODP DH KEX Groups for SSH       December 2017

   The United States Information Assurance Directorate (IAD) at the
   National Security Agency (NSA) has published "Commercial National
   Security Algorithm Suite and Quantum Computing Frequently Asked
   Questions".  [MFQ-U-OO-815099-15] is addressed to organizations that
   run classified or unclassified national security systems (NSS) and
   vendors that build products used in NSS.
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