Internet Engineering Task Force L. Velvindron, Ed.
Internet-Draft Hackers.mu
Intended status: Standards Track M. Baushke
Expires: November 13, 2017 Juniper Networks, Inc.
May 12, 2017
Increase minimum recommended modulus size to 2048 bits
draft-ietf-curdle-ssh-dh-group-exchange-00
Abstract
The Diffie-Hellman (DH) Group Exchange for the Secure Shell (SSH)
Transport layer Protocol specifies that servers and clients should
support groups with a modulus length of k bits, where the recommended
minumum value is 1024 bits. Recent security research has shown that
a minimum value of 1024 bits is insufficient against state-sponsored
actors. As such, this document formally updates RFC 4419 [RFC4419]
such that the minimum recommended value for k is 2048 bits and the
group size is 2048 bits at minimum.
Status of This Memo
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This Internet-Draft will expire on November 13, 2017.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
2. 2048 bits DH Group . . . . . . . . . . . . . . . . . . . . . 2
3. Security Considerations . . . . . . . . . . . . . . . . . . . 3
4. References . . . . . . . . . . . . . . . . . . . . . . . . . 3
4.1. Normative References . . . . . . . . . . . . . . . . . . 3
4.2. Informative References . . . . . . . . . . . . . . . . . 3
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 3
1. Introduction
RFC4419 [RFC4419] specifies a recommended minimum size of 1024 bits
for k, which is the modulus length of the DH Group. It also suggests
that in all cases, the size of the group needs be at least 1024 bits.
This document updates RFC 4419 [RFC4419] so that the minimum
recommended size be 2048 bits.
1.1. 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].
2. 2048 bits DH Group
Recent research [LOGJAM] strongly suggests that DH groups that are
1024 bits can be broken by state actors, and possibly an organization
with enough computing resources. The authors show how they are able
to break 768 bits DH group and extrapolate the attack to 1024 bits DH
groups. In their analysis, they show that breaking 1024 bits can be
done with enough computing resources. This document updates section
3 Paragraph 9 : Servers and clients SHOULD support groups with a
modulus length of k bits where 2048 <= k <= 8192. The recommended
minimum values for min and max are 2048 and 8192, respectively. This
document also updates Section 3 Paragraph 11: In all cases, ths size
of the group SHOULD be at least 2048 bits.
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3. Security Considerations
This document discusses security issues of DH groups that are 1024
bits in size, and formally updates the minimum size of DH groups to
be 2048 bits.
4. References
4.1. Normative References
[LOGJAM] Adrian, D., Bhargavan, K., Durumeric, Z., Gaudry, P.,
Green, M., Halderman, J., Heninger, N., Springall, D.,
ThomA(C), E., Valenta, L., VanderSloot, B., Wustrow, E.,
Zanella-BA(C)guelin, S., and P. Zimmermann, "Imperfect
Forward Secrecy: How Diffie-Hellman Fails in Practice",
ACM Conference on Computer and Communications Security
(CCS) 2015, 2015, <https://weakdh.org/imperfect-forward-
secrecy-ccs15.pdf>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
4.2. Informative References
[RFC4419] Friedl, M., Provos, N., and W. Simpson, "Diffie-Hellman
Group Exchange for the Secure Shell (SSH) Transport Layer
Protocol", RFC 4419, DOI 10.17487/RFC4419, March 2006,
<http://www.rfc-editor.org/info/rfc4419>.
Authors' Addresses
Loganaden Velvindron (editor)
Hackers.mu
88, Avenue De Plevitz
Roches Brunes
MU
Phone: +230 59762817
Email: logan@hackers.mu
Mark D. Baushke
Juniper Networks, Inc.
Email: mdb@juniper.net
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