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

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Last updated 2017-10-16 (latest revision 2017-09-15)
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Internet Engineering Task Force                               M. Baushke
Internet-Draft                                    Juniper Networks, Inc.
Updates: 4250, 4253 (if approved)                     September 15, 2017
Intended status: Standards Track
Expires: March 19, 2018

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


   This document defines added Modular Exponential (MODP) Groups for the
   Secure Shell (SSH) protocol using SHA-2 hashes.  This document
   updates RFC 4250.  This document updates RFC 4253 including an errata
   fix for checking the Peer's DH Public Key.

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
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   This Internet-Draft will expire on March 19, 2018.

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   include Simplified BSD License text as described in Section 4.e of

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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 3 of the [RFC4253] contains a small errata for checking the
   Peer's DH Public key.  Section 4 of this document provides the

   Due to 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 Diffie Hellman (DH) 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 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 group 15.  All use SHA512
   as the hash algorithm.

   The DH 2048-bit MODP group 14 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 the [RFC4253] section 6.4 and [RFC4250] section 4.10

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

   This FAQ document indicates that NSS should no longer use:

   o  ECDH and ECDSA with NIST P-256

   o  SHA-256

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   o  AES-128

   o  RSA with 2048-bit keys

   o  Diffie-Hellman with 2048-bit keys

   The FAQ also states that NSS users should select DH groups based upon
   well established and validated parameter sets that comply with the
   minimum required sizes.  Some specific examples include:
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