XMSS public key algorithms for the Secure Shell (SSH) protocol
draft-mu-curdle-ssh-xmss-00

Document Type Active Internet-Draft (individual)
Last updated 2019-10-28
Stream (None)
Intended RFC status (None)
Formats plain text xml pdf htmlized bibtex
Stream Stream state (No stream defined)
Consensus Boilerplate Unknown
RFC Editor Note (None)
IESG IESG state I-D Exists
Telechat date
Responsible AD (None)
Send notices to (None)
Internet Engineering Task Force                            L. Velvindron
Internet-Draft                                                 J. Daniel
Updates: RFC4253 (if approved)                             cyberstorm.mu
Intended status: Standards Track                        October 27, 2019
Expires: April 29, 2020

     XMSS public key algorithms for the Secure Shell (SSH) protocol
                      draft-mu-curdle-ssh-xmss-00

Abstract

   This document describes the use of the XMSS (XMSS: eXtended Merkle
   Signature Scheme) which is resistant to quantum computers attack, as
   a digital signature algorithm in the Secure Shell (SSH) protocol.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 29, 2020.

Copyright Notice

   Copyright (c) 2019 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.

Velvindron & Daniel      Expires April 29, 2020                 [Page 1]
Internet-Draft                XMSS for SSH                  October 2019

1.  Introduction

   Secure Shell (SSH) [RFC4251] is a secure remote-login protocol.  It
   provides for an extensible variety of public key algorithms for
   identifying servers and users to one another.  XMSS [RFC8391] is a
   digital signature system.  OpenSSH 7.7 [OpenSSH-7.7] introduced
   support for using XMSS for server and user authentication and was
   then followed by other SSH implementations.

   This document describes the method implemented by OpenSSH and others,
   and formalizes its use of the name "ssh-xmss".

   [TO BE REMOVED: Please send comments on this draft to
   curdle@ietf.org.]

2.  Conventions Used in This Document

   The descriptions of key and signature formats use the notation
   introduced in [RFC4251], Section 3 [RFC4251] and the string data type
   from [RFC4251], Section 5 [RFC4251].

2.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119] RFC
   8174 [RFC8174] when, and only when, they appear in all capitals, as
   shown here.

3.  Public Key Algorithm

   This document describes a public key algorithm for use with SSH in
   accordance with [RFC4253], Section 6.6 [RFC4253].  The name of the
   algorithm is "ssh-xmss".  This algorithm only supports signing and
   not encryption.

   Standard implementations of SSH SHOULD implement these signature
   algorithms.

4.  Public Key Format

   The "ssh-xmss" key format has the following encoding:

   string    "ssh-xmss"
   string    key

   Here 'key' is the 32-octet public key described by [RFC8391],
   Section 4.1.7 [RFC8391].

Velvindron & Daniel      Expires April 29, 2020                 [Page 2]
Internet-Draft                XMSS for SSH                  October 2019

5.  Signature Algorithm

   Signatures are generated according to the procedure in [RFC8391],
   Section 4.1.8 [RFC8391].

6.  Signature Format

   The "ssh-xmss" key format has the following encoding:

   string    "ssh-xmss"
   string    signature

   Here 'signature' is the 64-octet signature produced in accordance
   with [RFC8391], Section 4.1.9 [RFC8391].

7.  Verification Algorithm

   XMSS signatures are verified according to the procedure in [RFC8391],
   Section 4.1.10 [RFC8391].

8.  SSHFP DNS resource records

   Usage and generation of SSHFP DNS resource record is described in
   [RFC4255].  This section illustrates the generation of SSHFP resource
   records for "ssh-xmss" keys and the document specifies the
   corresponding xmss code point to the "SSHFP RR Types for public key
   algorithms" IANA registry.

   The generation of SSHFP resource records for "ssh-xmss" keys is
   described as follows.

   The encoding of xmss public keys is described in [RFC8391].  In
   brief, an xmss public key is a 57-octet value representing a 455-bit
   y-coordinate of an elliptic curve point, and a sign bit indicating
   the the corresponding x-coordinate.

   The SSHFP Resource Record for the xmss public key with SHA-256
   fingerprint would for example be:

   example.com.  IN SSHFP TBD 2 ( a87f1b687ac0e57d2a081a2f2826723
   34d90ed316d2b818ca9580ea384d924 01 )

   The 2 here indicates SHA-256 [RFC6594].

Velvindron & Daniel      Expires April 29, 2020                 [Page 3]
Internet-Draft                XMSS for SSH                  October 2019

9.  IANA Considerations

   This document augments the Public Key Algorithm Names in [RFC4250],
   Section 4.6.2 [RFC4250].

   IANA is requested to add to the Public Key Algorithm Names registry
   [IANA-PKA] with the following entry:

                   Public Key Algorithm Name Reference
                   ------------------------- ----------
                   ssh-xmss                  This Draft

   IANA is requested to add the following entry to the "SSHFP RR Types
   for public key algorithms" registry [IANA-SSHFP]:

   +--------+-------------+------------+

   | Value | Description | Reference |

   +--------+-------------+------------+

   | TBD | xmss | [this-draft] |

   +--------+-------------+------------+

   We strongly suggest 5 as value.

   [TO BE REMOVED: This registration should take place at the following
   location: <http://www.iana.org/assignments/ssh-parameters/ssh-
   parameters.xhtml#ssh-parameters-19>]

10.  Security Considerations

   The security considerations in [RFC4251], Section 9 [RFC4251] apply
   to all SSH implementations, including those using xmss.

   The security considerations in [RFC8391], Section 8 [RFC8391] apply
   to all uses of xmss including those in SSH.

11.  Acknowledgements

   The OpenSSH implementation of XMSS in SSH was written by Markus
   Friedl.  We are also grateful to Daniel Migault for their comments.

Velvindron & Daniel      Expires April 29, 2020                 [Page 4]
Internet-Draft                XMSS for SSH                  October 2019

12.  References

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC4250]  Lehtinen, S. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Protocol Assigned Numbers", RFC 4250,
              DOI 10.17487/RFC4250, January 2006,
              <https://www.rfc-editor.org/info/rfc4250>.

   [RFC4251]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251,
              January 2006, <https://www.rfc-editor.org/info/rfc4251>.

   [RFC4253]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253,
              January 2006, <https://www.rfc-editor.org/info/rfc4253>.

   [RFC4255]  Schlyter, J. and W. Griffin, "Using DNS to Securely
              Publish Secure Shell (SSH) Key Fingerprints", RFC 4255,
              DOI 10.17487/RFC4255, January 2006,
              <https://www.rfc-editor.org/info/rfc4255>.

   [RFC6594]  Sury, O., "Use of the SHA-256 Algorithm with RSA, Digital
              Signature Algorithm (DSA), and Elliptic Curve DSA (ECDSA)
              in SSHFP Resource Records", RFC 6594,
              DOI 10.17487/RFC6594, April 2012,
              <https://www.rfc-editor.org/info/rfc6594>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8391]  Huelsing, A., Butin, D., Gazdag, S., Rijneveld, J., and A.
              Mohaisen, "XMSS: eXtended Merkle Signature Scheme",
              RFC 8391, DOI 10.17487/RFC8391, May 2018,
              <https://www.rfc-editor.org/info/rfc8391>.

12.2.  Informative References

Velvindron & Daniel      Expires April 29, 2020                 [Page 5]
Internet-Draft                XMSS for SSH                  October 2019

   [IANA-PKA]
              Internet Assigned Numbers Authority (IANA), "Secure Shell
              (SSH) Protocol Parameters: Public Key Algorithm Names",
              May 2017, <http://www.iana.org/assignments/ssh-parameters/
              ssh-parameters.xhtml#ssh-parameters-19>.

   [IANA-SSHFP]
              Internet Assigned Numbers Authority (IANA), "Secure Shell
              (SSH) Protocol Parameters: Public Key Algorithm Names",
              May 2017, <https://www.iana.org/assignments/dns-sshfp-rr-
              parameters/dns-sshfp-rr-parameters.xhtml#dns-sshfp-rr-
              parameters-1>.

   [OpenSSH-7.7]
              Friedl, M., Provos, N., de Raadt, T., Steves, K., Miller,
              D., Tucker, D., Rice, T., and B. Lindstrom, "OpenSSH 7.7
              release notes", January 2018,
              <http://www.openssh.com/txt/release-7.7>.

Authors' Addresses

   Loganaden Velvindron
   cyberstorm.mu
   Avenue De Plevitz
   Roches Brunes
   Mauritius

   Email: logan@cyberstorm.mu

   Jeremie Daniel
   cyberstorm.mu
   25C, Thompson Road
   Vacoas
   Mauritius

   Email: jeremie@cyberstorm.mu

Velvindron & Daniel      Expires April 29, 2020                 [Page 6]