One document matched: draft-josefsson-ssh-curves-00.txt
Network Working Group A. Adamantiadis
Internet-Draft libssh
Intended status: Informational S. Josefsson
Expires: May 9, 2016 SJD AB
November 6, 2015
Secure Shell (SSH) Key Exchange Method using Curve25519 and Curve448
draft-josefsson-ssh-curves-00
Abstract
How to implement the Curve25519 and Curve448 key exchange methods in
the Secure Shell (SSH) protocol is described.
Status of This Memo
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This Internet-Draft will expire on May 9, 2016.
Copyright Notice
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Internet-Draft Curve25519/448 for SSH November 2015
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Key Exchange Methods . . . . . . . . . . . . . . . . . . . . 2
3. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 3
4. Security Considerations . . . . . . . . . . . . . . . . . . . 3
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 3
6.1. Normative References . . . . . . . . . . . . . . . . . . 3
6.2. Informative References . . . . . . . . . . . . . . . . . 4
Appendix A. Copying conditions . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 4
1. Introduction
In [Curve25519], a new elliptic curve function for use in
cryptographic applications was introduced. In [Ed448-Goldilocks] the
Ed448-Goldilocks curve (also known as Curve448) is described. In
[I-D.irtf-cfrg-curves], the Diffie-Hellman functions using Curve25519
and Curve448 are specified.
Secure Shell (SSH) [RFC4251] is a secure remote login protocol. The
key exchange key exchange protocol described in [RFC4253] supports an
extensible set of methods. In [RFC5656] it is described how elliptic
curves are integrated in SSH, and this document re-use those protocol
messages.
This document describe how key exchange is achieved based on
Curve25519 and Curve448 in SSH. For Curve25519 what we described is
identical to an already implemented (in libssh and OpenSSH) and
widely deployed proposal registered in the private namespace
("curve25519-sha256@libssh.org"). The Curve448 key exchange method
is novel but similar in spirit.
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].
2. Key Exchange Methods
The key exchange procedure is identical to the one described RFC 5656
chapter 4 of [RFC5656]. Public ephemeral keys are transmitted over
SSH encapsulated into standard SSH strings.
The method names registered by this document are "curve25519-sha256"
and "curve448-sha256".
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The whole method is based on the Curve25519 and Curve448 scalar
multiplication, as described in [I-D.irtf-cfrg-curves]. Private and
public keys are generated as described therein, and no special
validation is required beyond what is discussed there. Public keys
are defined as strings of 32 bytes for Curve25519 and 56 bytes for
Curve448. The derived shared secret is is 32 bytes when Curve25519
is used and 56 bytes when Curve448 is used.
The shared secret, k, is defined in SSH specifications to be a big
integer. This number is calculated as follows. X is the 32 bytes
point obtained by the scalar multiplication of the other side's
public key and the local private key scalar. The whole 32 bytes of
the number X are then converted into a big integer k. This
conversion follows the network byte order. This step differs from
[RFC5656].
3. Acknowledgements
The "curve25519-sha256" key exchange method is identical to the
"curve25519-sha256@libssh.org" key exchange method created by Aris
Adamantiadis and implemented in libssh and OpenSSH.
4. Security Considerations
The security considerations of [RFC4251], [RFC5656], and
[I-D.irtf-cfrg-curves] are inherited.
5. IANA Considerations
IANA is requested to add "curve25519-sha256" and "curve448-sha256" to
the "Key Exchange Method Names" registry for SSH that was created in
RFC 4250 section 4.10 [RFC4250].
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4250] Lehtinen, S. and C. Lonvick, Ed., "The Secure Shell (SSH)
Protocol Assigned Numbers", RFC 4250, DOI 10.17487/
RFC4250, January 2006,
<http://www.rfc-editor.org/info/rfc4250>.
[RFC4251] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
Protocol Architecture", RFC 4251, January 2006.
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Internet-Draft Curve25519/448 for SSH November 2015
[RFC4253] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253,
January 2006, <http://www.rfc-editor.org/info/rfc4253>.
[RFC5656] Stebila, D. and J. Green, "Elliptic Curve Algorithm
Integration in the Secure Shell Transport Layer", RFC
5656, DOI 10.17487/RFC5656, December 2009,
<http://www.rfc-editor.org/info/rfc5656>.
[I-D.irtf-cfrg-curves]
Langley, A. and M. Hamburg, "Elliptic Curves for
Security", draft-irtf-cfrg-curves-10 (work in progress),
October 2015.
6.2. Informative References
[Curve25519]
Bernstein, J., "Curve25519: New Diffie-Hellman Speed
Records", LNCS 3958, pp. 207-228, February 2006,
<http://dx.doi.org/10.1007/11745853_14>.
[Ed448-Goldilocks]
Hamburg, , "Ed448-Goldilocks, a new elliptic curve", June
2015, <https://eprint.iacr.org/2015/625>.
Appendix A. Copying conditions
Regarding this entire document or any portion of it, the authors
makes no guarantees and is not responsible for any damage resulting
from its use. The authors grants irrevocable permission to anyone to
use, modify, and distribute it in any way that does not diminish the
rights of anyone else to use, modify, and distribute it, provided
that redistributed derivative works do not contain misleading author
or version information. Derivative works need not be licensed under
similar terms.
Authors' Addresses
Aris Adamantiadis
libssh
Email: aris@badcode.be
Simon Josefsson
SJD AB
Email: simon@josefsson.org
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