Increase the Secure Shell Minimum Recommended Diffie-Hellman Modulus Size to 2048 Bits
draft-ietf-curdle-ssh-dh-group-exchange-06

[Ballot comment]
RFC4419 specifies an example in Appendix A that uses a 1024 bit safe prime. Shouldn't this Appendix be updated by the draft as well?

[Ballot comment]
Sue, in her OPS DIR review, brought up a good point.
This document does not indicate whether it is wise for the operations system to log a report if it receives a less than 2048 bits. 
Would this enhance security or provide DoS attack surface.  If logging creates a DoS surface, it would be good to include this as operational advice.

[Ballot comment]
I share the questions about "SHOULD" vs "MUST".

- abstract: "insufficient against state-sponsored
  actors, and possibly an organization with enough computing resources"

Should "an" be "any"?  (Same question for section 2).

[Ballot comment]
I do agree with Spencer, the text that is non-normative reads as if this is fully deprecating any recommendation below 2048, but then the normative text just says SHOULD.  Is there a reason this is not MUST?  I know deprecating things takes a long time.

[Ballot comment]
So, I see that the recommendations are mostly SHOULDs.

Is this, perhaps, for backward compatibility with SSH implementations that don't implement this specification?

This isn't remotely something I'm smart about, but I do wonder about bid-down attacks to, say, 1024. Is that possible?

[Ballot comment]
Minor nit:

Section 2.  2048 bits DH Group
"It also suggests that in all cases, the size of the group needs be at least 1024 bits.This document updates [RFC4419] as described below:"
s/bits.This/bits. This/ (missing space).

(Via drafts-lastcall@iana.org): IESG/Authors/WG Chairs:

The IANA Services Operator has reviewed draft-ietf-curdle-ssh-dh-group-exchange-04, which is currently in Last Call, and has the following comments:

We understand that this document doesn't require any registry actions.

While it's often helpful for a document's IANA Considerations section to remain in place upon publication even if there are no actions, if the authors strongly prefer to remove it, we do not object.

If this assessment is not accurate, please respond as soon as possible.

Thank you,

Sabrina Tanamal
IANA Services Specialist
PTI

The following Last Call announcement was sent out (ends 2017-07-30):

From: The IESG
To: IETF-Announce
CC: ekr@rtfm.com, draft-ietf-curdle-ssh-dh-group-exchange@ietf.org, Daniel Migault , curdle-chairs@ietf.org, curdle@ietf.org, daniel.migault@ericsson.com
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (Increase SSH minimum recommended DH modulus size to 2048 bits) to Proposed Standard


The IESG has received a request from the CURves, Deprecating and a Little
more Encryption WG (curdle) to consider the following document: - 'Increase
SSH minimum recommended DH modulus size to 2048 bits'
  as Proposed Standard

The IESG plans to make a decision in the next few weeks, and solicits final
comments on this action. Please send substantive comments to the
ietf@ietf.org mailing lists by 2017-07-30. Exceptionally, comments may be
sent to iesg@ietf.org instead. In either case, please retain the beginning of
the Subject line to allow automated sorting.

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 the specification
  such that the minimum recommended value for k is 2048 bits and the
  group size is 2048 bits at minimum.  This RFC updates RFC4419 which
  allowed for DH moduli less than 2048 bits.




The file can be obtained via
https://datatracker.ietf.org/doc/draft-ietf-curdle-ssh-dh-group-exchange/

IESG discussion can be tracked via
https://datatracker.ietf.org/doc/draft-ietf-curdle-ssh-dh-group-exchange/ballot/


No IPR declarations have been submitted directly on this I-D.

As required by RFC 4858, this is the current template for the Document
Shepherd Write-Up.

Changes are expected over time. This version is dated 24 February 2012.

(1) What type of RFC is being requested (BCP, Proposed Standard,
Internet Standard, Informational, Experimental, or Historic)?  Why
is this the proper type of RFC?  Is this type of RFC indicated in the
title page header?

The intended status is "Standards Track". This is the appropriated
status as the document updates RFC 4419 which is of type "Standards Track". 
The type is also justified as the document affects interoperability.
This document formally updates the specification such that the minimum
recommended value for k is 2048 bits and the group size is 2048 bits at
minimum.  This RFC updates RFC4419 which allowed for DH moduli less
than 2048 bits.
 
(2) The IESG approval announcement includes a Document Announcement
Write-Up. Please provide such a Document Announcement Write-Up. Recent
examples can be found in the "Action" announcements for approved
documents. The approval announcement contains the following sections:

Technical Summary

  Relevant content can frequently be found in the abstract
  and/or introduction of the document. If not, this may be
  an indication that there are deficiencies in the abstract
  or introduction.

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 the specification
such that the minimum recommended value for k is 2048 bits and the
group size is 2048 bits at minimum.  This RFC updates RFC4419 which
allowed for DH moduli less than 2048 bits.

The update of RFC 4419 is mentioned in the header, the abstract and the introduction.

Working Group Summary

  Was there anything in WG process that is worth noting? For
  example, was there controversy about particular points or
  were there decisions where the consensus was particularly
  rough?

No controversy were noted.

Document Quality

  Are there existing implementations of the protocol? Have a
  significant number of vendors indicated their plan to
  implement the specification? Are there any reviewers that
  merit special mention as having done a thorough review,
  e.g., one that resulted in important changes or a
  conclusion that the document had no substantive issues? If
  there was a MIB Doctor, Media Type or other expert review,
  what was its course (briefly)? In the case of a Media Type
  review, on what date was the request posted?

At least one Open Source implementation has implemented this:
OpenSSH:
http://freshbsd.org/commit/openbsd/2a2c1e4e7e3fcc787fa334f50347ee1d282fac45

Personnel

  Who is the Document Shepherd? Who is the Responsible Area
  Director?

Daniel Migault is the document shepherd, Eric Rescola is the AD.

(3) Briefly describe the review of this document that was performed by
the Document Shepherd.  If this version of the document is not ready
for publication, please explain why the document is being forwarded to
the IESG.

I reviewed the document and I think it is ready.

(4) Does the document Shepherd have any concerns about the depth or
breadth of the reviews that have been performed?

No.

(5) Do portions of the document need review from a particular or from
broader perspective, e.g., security, operational complexity, AAA, DNS,
DHCP, XML, or internationalization? If so, describe the review that
took place.

No.

(6) Describe any specific concerns or issues that the Document Shepherd
has with this document that the Responsible Area Director and/or the
IESG should be aware of? For example, perhaps he or she is uncomfortable
with certain parts of the document, or has concerns whether there really
is a need for it. In any event, if the WG has discussed those issues and
has indicated that it still wishes to advance the document, detail those
concerns here.

I have no concerns.

(7) Has each author confirmed that any and all appropriate IPR
disclosures required for full conformance with the provisions of BCP 78
and BCP 79 have already been filed. If not, explain why.

The authors conformed they are not aware of any IPR.

(8) Has an IPR disclosure been filed that references this document?
If so, summarize any WG discussion and conclusion regarding the IPR
disclosures.

This does not apply here.

(9) How solid is the WG consensus behind this document? Does it
represent the strong concurrence of a few individuals, with others
being silent, or does the WG as a whole understand and agree with it? 

The WG agree with it.

(10) Has anyone threatened an appeal or otherwise indicated extreme
discontent? If so, please summarise the areas of conflict in separate
email messages to the Responsible Area Director. (It should be in a
separate email because this questionnaire is publicly available.)

No.

(11) Identify any ID nits the Document Shepherd has found in this
document. (See https://www.ietf.org/tools/idnits/ and the Internet-Drafts
Checklist). Boilerplate checks are not enough; this check needs to be
thorough.

The nits provides the following below. The disclaimer might seem necessary as
the current document describes how RFC4419 is updated by the current document.

  -- The document seems to contain a disclaimer for pre-RFC5378 work, and may
    have content which was first submitted before 10 November 2008.  The
    disclaimer is necessary when there are original authors that you have
    been unable to contact, or if some do not wish to grant the BCP78 rights
    to the IETF Trust.  If you are able to get all authors (current and
    original) to grant those rights, you can and should remove the
    disclaimer; otherwise, the disclaimer is needed and you can ignore this
    comment. (See the Legal Provisions document at
    http://trustee.ietf.org/license-info for more information.)

(12) Describe how the document meets any required formal review
criteria, such as the MIB Doctor, media type, and URI type reviews.

(13) Have all references within this document been identified as
either normative or informative?

Yes.

(14) Are there normative references to documents that are not ready for
advancement or are otherwise in an unclear state? If such normative
references exist, what is the plan for their completion?

No.

(15) Are there downward normative references references (see RFC 3967)?
If so, list these downward references to support the Area Director in
the Last Call procedure.

No.

(16) Will publication of this document change the status of any
existing RFCs? Are those RFCs listed on the title page header, listed
in the abstract, and discussed in the introduction? If the RFCs are not
listed in the Abstract and Introduction, explain why, and point to the
part of the document where the relationship of this document to the
other RFCs is discussed. If this information is not in the document,
explain why the WG considers it unnecessary.

This document changes the status of RFC4419. This is mentioned in
the header, abstract and introduction.

(17) Describe the Document Shepherd's review of the IANA considerations
section, especially with regard to its consistency with the body of the
document. Confirm that all protocol extensions that the document makes
are associated with the appropriate reservations in IANA registries.
Confirm that any referenced IANA registries have been clearly
identified. Confirm that newly created IANA registries include a
detailed specification of the initial contents for the registry, that
allocations procedures for future registrations are defined, and a
reasonable name for the new registry has been suggested (see RFC 5226).

There is no IANA considerations.

(18) List any new IANA registries that require Expert Review for future
allocations. Provide any public guidance that the IESG would find
useful in selecting the IANA Experts for these new registries.

This does not apply here.

(19) Describe reviews and automated checks performed by the Document
Shepherd to validate sections of the document written in a formal
language, such as XML code, BNF rules, MIB definitions, etc.

This does not apply here.