Key Exchange (KEX) Method Updates and Recommendations for Secure Shell (SSH)
draft-ietf-curdle-ssh-kex-sha2-13

Document Type Active Internet-Draft (curdle WG)
Author Mark Baushke 
Last updated 2021-01-14
Replaces draft-baushke-ssh-dh-group-sha2
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Internet Engineering Task Force                            M. D. Baushke
Internet-Draft                                    Juniper Networks, Inc.
Updates: 4250 4253 4432 4462 (if approved)               14 January 2021
Intended status: Standards Track                                        
Expires: 18 July 2021

 Key Exchange (KEX) Method Updates and Recommendations for Secure Shell
                                 (SSH)
                   draft-ietf-curdle-ssh-kex-sha2-13

Abstract

   This document is intended to update the recommended set of key
   exchange methods for use in the Secure Shell (SSH) protocol to meet
   evolving needs for stronger security.  This document updates RFC
   4250, RFC 4253, RFC 4432, and RFC 4462.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on 18 July 2021.

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   Copyright (c) 2021 IETF Trust and the persons identified as the
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Baushke                   Expires 18 July 2021                  [Page 1]
Internet-Draft  KEX Method Updates/Recommendations for S    January 2021

Table of Contents

   1.  Overview and Rationale  . . . . . . . . . . . . . . . . . . .   2
     1.1.  Selecting an appropriate hashing algorithm  . . . . . . .   3
     1.2.  Selecting an appropriate Public Key Algorithm . . . . . .   3
       1.2.1.  Elliptic Curve Cryptography (ECC) . . . . . . . . . .   4
       1.2.2.  Finite Field Cryptography (FFC) . . . . . . . . . . .   4
       1.2.3.  Integer Factorization Cryptography (IFC)  . . . . . .   5
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   5
   3.  Key Exchange Methods  . . . . . . . . . . . . . . . . . . . .   6
     3.1.  SHA-1 and SHA-2 Hashing . . . . . . . . . . . . . . . . .   6
     3.2.  Elliptic Curve Cryptography (ECC) . . . . . . . . . . . .   6
       3.2.1.  curve25519-sha256 and gss-curve25519-sha256-* . . . .   6
       3.2.2.  curve448-sha512 and gss-curve448-sha512-* . . . . . .   7
       3.2.3.  ECC diffie-hellman using ecdh-*, ecmqv-sha2, and
               gss-nistp*  . . . . . . . . . . . . . . . . . . . . .   7
     3.3.  Finite Field Cryptography (FFC) . . . . . . . . . . . . .   8
       3.3.1.  FFC diffie-hellman using generated MODP groups  . . .   8
       3.3.2.  FFC diffie-hellman using named MODP groups  . . . . .   8
     3.4.  Integer Factorization Cryptography (IFC)  . . . . . . . .   9
     3.5.  Secure Shell Extension Negotiation  . . . . . . . . . . .   9
   4.  Summary Guidance for Key Exchange Method Names
           Implementations . . . . . . . . . . . . . . . . . . . . .   9
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Overview and Rationale

   Secure Shell (SSH) is a common protocol for secure communication on
   the Internet.  In [RFC4253], SSH originally defined two Key Exchange
   (KEX) Method Names that MUST be implemented.  Over time what was once
   considered secure is no longer considered secure.  The purpose of
   this RFC is to recommend that some published key exchanges be
   deprecated as well as recommending some that SHOULD and one that MUST
   be adopted.  This document updates [RFC4250] [RFC4253] [RFC4432]
   [RFC4462] by changing the requirement level ("MUST" moving to
   "SHOULD" or "MAY" or "SHOULD NOT", and "MAY" moving to "MUST" or
   "SHOULD" or "SHOULD NOT" or "MUST NOT") of various key-exchange
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