Internet DRAFT - draft-mu-curdle-ssh-xmss
draft-mu-curdle-ssh-xmss
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
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This Internet-Draft will expire on April 29, 2020.
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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].
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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].
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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.
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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
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[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
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