Increase the Secure Shell Minimum Recommended Diffie-Hellman Modulus Size to 2048 Bits
RFC 8270
| Document | Type |
RFC - Proposed Standard
(December 2017; Errata)
Updates RFC 4419
|
|
|---|---|---|---|
| Last updated | 2018-09-24 | ||
| Stream | IETF | ||
| Formats | plain text html pdf htmlized bibtex | ||
| Reviews | |||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Daniel Migault | ||
| Shepherd write-up | Show (last changed 2017-07-11) | ||
| IESG | IESG state | RFC 8270 (Proposed Standard) | |
| Consensus Boilerplate | Yes | ||
| Telechat date | |||
| Responsible AD | Eric Rescorla | ||
| Send notices to | Daniel Migault <daniel.migault@ericsson.com> | ||
| IANA | IANA review state | Version Changed - Review Needed | |
| IANA action state | No IANA Actions | ||
Internet Engineering Task Force (IETF) L. Velvindron
Request for Comments: 8270 Hackers.mu
Updates: 4419 M. Baushke
Category: Standards Track Juniper Networks, Inc.
ISSN: 2070-1721 December 2017
Increase the Secure Shell Minimum Recommended
Diffie-Hellman Modulus Size to 2048 Bits
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 minimum modulus group size of 1024 bits.
Recent security research has shown that the minimum value of 1024
bits is insufficient to protect against state-sponsored actors and
any organization with enough computing resources. This RFC updates
RFC 4419, which allowed for DH moduli less than 2048 bits; now, 2048
bits is the minimum acceptable group size.
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
https://www.rfc-editor.org/info/rfc8270.
Velvindron & Baushke Standards Track [Page 1]
RFC 8270 Recommended Minimum Modulus Size December 2017
Copyright Notice
Copyright (c) 2017 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
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 2
3. 2048-Bit DH Group . . . . . . . . . . . . . . . . . . . . . . 3
4. Interoperability . . . . . . . . . . . . . . . . . . . . . . 3
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
7.1. Normative References . . . . . . . . . . . . . . . . . . 4
7.2. Informative References . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
[RFC4419] specifies a recommended minimum DH modulus group size of
1024 bits. It also suggests that in all cases, the size of the group
needs to be at least 1024 bits. This document updates [RFC4419] so
that the minimum recommended size is 2048 bits. This recommendation
is based on recent research [LOGJAM] on DH group weaknesses. This
minimum DH group size may need to be increased to 3072 for forward-
looking users.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"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.
Velvindron & Baushke Standards Track [Page 2]
RFC 8270 Recommended Minimum Modulus Size December 2017
3. 2048-Bit DH Group
Recent research [LOGJAM] strongly suggests that DH groups that are
1024 bits can be broken by state-sponsored actors and any
organization with enough computing resources. The authors show how
they are able to break 768-bit DH groups and extrapolate the attack
to 1024-bit DH groups. In their analysis, they show that breaking
1024 bits can be done with sufficient computing resources. This
document provides the following recommendation: SSH servers and SSH
clients SHOULD support groups with a minimum acceptable group size of
2048 bits for the "min" value of the SSH_MSG_KEY_DH_GEX_REQUEST
client message given in [RFC4419]. Further, SSH clients SHOULD be
able to send a value of 3072 bits for the preferred acceptable group
size "n" in the SSH_MSG_KEY_DH_GEX_REQUEST message.
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