Generic Security Service Application Program Interface (GSS-API) Key Exchange with SHA-2
RFC 8732

Document Type RFC - Proposed Standard (February 2020; No errata)
Updates RFC 4462
Authors Simo Sorce  , Hubert Kario 
Last updated 2020-02-28
Replaces draft-ssorce-gss-keyex-sha2
Stream Internent Engineering Task Force (IETF)
Formats plain text html xml pdf htmlized (tools) htmlized bibtex
Stream WG state Submitted to IESG for Publication
Document shepherd Daniel Migault
Shepherd write-up Show (last changed 2018-02-23)
IESG IESG state RFC 8732 (Proposed Standard)
Action Holders
Consensus Boilerplate Yes
Telechat date
Responsible AD Benjamin Kaduk
Send notices to Daniel Migault <>
IANA IANA review state Version Changed - Review Needed
IANA action state RFC-Ed-Ack

Internet Engineering Task Force (IETF)                          S. Sorce
Request for Comments: 8732                                      H. Kario
Updates: 4462                                              Red Hat, Inc.
Category: Standards Track                                  February 2020
ISSN: 2070-1721

  Generic Security Service Application Program Interface (GSS-API) Key
                          Exchange with SHA-2


   This document specifies additions and amendments to RFC 4462.  It
   defines a new key exchange method that uses SHA-2 for integrity and
   deprecates weak Diffie-Hellman (DH) groups.  The purpose of this
   specification is to modernize the cryptographic primitives used by
   Generic Security Service (GSS) key exchanges.

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

Copyright Notice

   Copyright (c) 2020 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
   ( 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.

Table of Contents

   1.  Introduction
   2.  Rationale
   3.  Document Conventions
   4.  New Diffie-Hellman Key Exchange Methods
   5.  New Elliptic Curve Diffie-Hellman Key Exchange Methods
     5.1.  Generic GSS-API Key Exchange with ECDH
     5.2.  ECDH Key Exchange Methods
   6.  Deprecated Algorithms
   7.  IANA Considerations
   8.  Security Considerations
     8.1.  New Finite Field DH Mechanisms
     8.2.  New Elliptic Curve DH Mechanisms
     8.3.  GSS-API Delegation
   9.  References
     9.1.  Normative References
     9.2.  Informative References
   Authors' Addresses

1.  Introduction

   Secure Shell (SSH) Generic Security Service Application Program
   Interface (GSS-API) methods [RFC4462] allow the use of GSS-API
   [RFC2743] for authentication and key exchange in SSH.  [RFC4462]
   defines three exchange methods all based on DH groups and SHA-1.
   This document updates [RFC4462] with new methods intended to support
   environments that desire to use the SHA-2 cryptographic hash

2.  Rationale

   Due to security concerns with SHA-1 [RFC6194] and with modular
   exponentiation (MODP) groups with less than 2048 bits
   [NIST-SP-800-131Ar2], we propose the use of hashes based on SHA-2
   [RFC6234] with DH group14, group15, group16, group17, and group18
   [RFC3526].  Additionally, we add support for key exchange based on
   Elliptic Curve Diffie-Hellman with the NIST P-256, P-384, and P-521
   [SEC2v2], as well as the X25519 and X448 [RFC7748] curves.  Following
   the practice of [RFC8268], only SHA-256 and SHA-512 hashes are used
   for DH groups.  For NIST curves, the same curve-to-hashing algorithm
   pairing used in [RFC5656] is adopted for consistency.

3.  Document Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

4.  New Diffie-Hellman Key Exchange Methods

   This document adopts the same naming convention defined in [RFC4462]
   to define families of methods that cover any GSS-API mechanism used
   with a specific Diffie-Hellman group and SHA-2 hash combination.

       | Key Exchange Method Name | Implementation Recommendations |
       | gss-group14-sha256-*     | SHOULD/RECOMMENDED             |
       | gss-group15-sha512-*     | MAY/OPTIONAL                   |
       | gss-group16-sha512-*     | SHOULD/RECOMMENDED             |
       | gss-group17-sha512-*     | MAY/OPTIONAL                   |
Show full document text