Secure Shell (SSH) Key Exchange Method Using Curve25519 and Curve448
draft-ietf-curdle-ssh-curves-12

[Ballot comment]
(1) Section 1.  Please provide informative reference to libssh and OpenSSH.

(2) Section 5. Per the second paragraph of this section, I would recommend being clearer on the differences and similarities of both algorithms so implementers understand the tradeoffs.  Specifically:

-- Curve25519 is “strong” (Section 1 says ~128 bits) and Curve448 “hasn’t received the same cryptographic review” – these seem like unequal statements.

-- Curve 25519 makes the claims of being “efficient on a wide range of architecture” and “better implementations properties compared to traditional elliptical curves”.  Curve448 “is similar … and is slower”.  So is it inefficient across architectures? Worst implementation properties?  Can anything be said to qualify “slower”?

-- I recommend moving the guidance on what is recommend and why to be in this section so the rational is in one place (rather than also being in Section 1, “This document provide Curve25519 as the preferred choice, …”)

(3) Appendix A: As other ballots have noted, is this section needed?

(4) Editorial Nits:
-- Section 3.  s/chapter 4/section 4/g

-- Section 3.1.  The text “… passed to the ECDH code in SSH that …” reads like a given implementation is being discussed.  Perhaps “passed to the ECDH function” (or ECDH algorithm).

-- Section 1.  Per “The Curve448 key exchange method is similar but uses SHA-512 [RFC6234] to further separate it from the Curve25519 alternative.”, I recommend dropping the ending clause of “to further separate it from the Curve22519 alternative”.  The subsequent text (in the Security Considerations) appear to already cover that it is an alternative.

[Ballot comment]
Thanks for the work on documenting this key exchange method.

I'm a little surprised that there is no discussion of deployment considerations for deploying "curve25519-sha256" into an environment in which "curve25519-sha256@libssh.org" is already well-established (as described in the introduction), or of sunsetting the vendor-specific version. Some advice on which algorithms to offer and which ones to accept would probably be worthwhile, especially if there is any long-term hope of retiring the "curve25519-sha256@libssh.org" designator in favor of the standard one.

[Ballot comment]
Mirja beat me to it with the questions re: the additional Copyright text -- I'd *thought* I'd seen a reply to that mail, but cannot seem to find it at the moment..

Also:
"An abort for these purposes is defined as a disconnect of the session with an appropriate SSH "protocol error" for the fault provided to or by the client. "
Fair enough -- but would it be possible to point at where people can go find out what the "appropriate SSH protocol error" is?

[Ballot discuss]
Thank you for the hard work put into this  document.

Please note that I second Mirja's discuss about the 'copying' text. And, please find below an easy-to-fix DISCUSS and some COMMENTs.

Regards,

-éric

== DISCUSS ==

-- Abstract --

For a standard track document, I find it weird to write 'conventions' rather than specification. Easy to fix.

[Ballot comment]
== COMMENTS ==

-- Section 1 --
" At the time of writing this specification" will look strange in a couple of years, please state 2019.

-- Section 3 --
I am not a SSH expert, but, can you add a reference to X25519 (in RFC 7748?) if not obvious for SSH experts ?

== NITS ==

-- Section 1 --
s/This document provide Curve25519/This document provides Curve25519/
s/Curve25519 has been/Curve25519 have been/

From now on, I am stopping to review for nits, typos and grammar errors. Please run a spell checker.

[Ballot comment]
The following text in Section 1:

  At the time of writing this specification, high-quality free
  implementations of Curve25519 has been in deployed use for several
  years, while Curve448 implementations are slowly appearing, so it is
  accepted that adoption of Curve448 would be slower.

would not age well once the RFC is published. I suggest this is moved from the draft to the shepherding write-up.


Also, SHA-256 and SHA-512 need to be normative references.

[Ballot comment]
The following text in Section 1:

  At the time of writing this specification, high-quality free
  implementations of Curve25519 has been in deployed use for several
  years, while Curve448 implementations are slowly appearing, so it is
  accepted that adoption of Curve448 would be slower.

would not age well once the RFC is published. I suggest this is moved from the draft to the shepherding write-up.

[Ballot discuss]
Question to the IESG/responsible AD:

I found this:

"Appendix A.  Copying conditions

  Regarding this entire document or any portion of it, the authors make
  no guarantees and are not responsible for any damage resulting from
  its use.  The authors grant 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."

Does it make sense to have this in addition to the usual IETF terms? And/or why is this needed here?

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

The IANA Functions Operator has completed its review of draft-ietf-curdle-ssh-curves-09. If any part of this review is inaccurate, please let us know.

The IANA Functions Operator understands that, upon approval of this document, there is a single action which we must complete.

In the Key Exchange Method Names registry on the Secure Shell (SSH) Protocol Parameters registry page located at:

https://www.iana.org/assignments/ssh-parameters/

two new registrations are to be made as follows:

Method Name: curve25519-sha256
Reference: [ RFC-to-be ]
Note:

Method Name: curve448-sha512
Reference: [ RFC-to-be ]
Note:

The IANA Functions Operator understands that this is the only action required to be completed upon approval of this document.

Note:  The actions requested in this document will not be completed until the document has been approved for publication as an RFC. This message is meant only to confirm the list of actions that will be performed.

Thank you,

Sabrina Tanamal
Senior IANA Services Specialist

The following Last Call announcement was sent out (ends 2019-08-26):

From: The IESG
To: IETF-Announce
CC: curdle@ietf.org, draft-ietf-curdle-ssh-curves@ietf.org, Daniel Migault , curdle-chairs@ietf.org, daniel.migault@ericsson.com, kaduk@mit.edu
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (Secure Shell (SSH) Key Exchange Method using Curve25519 and Curve448) 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: - 'Secure
Shell (SSH) Key Exchange Method using Curve25519 and Curve448'
  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 2019-08-26. 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


  This document describes the conventions for using Curve25519 and
  Curve448 key exchange methods in the Secure Shell (SSH) protocol.




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

IESG discussion can be tracked via
https://datatracker.ietf.org/doc/draft-ietf-curdle-ssh-curves/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?

This document describes the conventions for using Curve25519 and
Curve448 key exchange methods in the Secure Shell (SSH) protocol.
It defines code points in the registry, conventions guarantee
inter-operability, so standard track is the appropriated type.  The
intended status in the header is set to "Standard Track". 

(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.

This document describes the conventions for using Curve25519 and
Curve448 key exchange methods in the Secure Shell (SSH) protocol.

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?

The document had non controversy and had few reviews outside
the authors. However, the document is not controversial in nature,
and mostly  describes a mechanism implemented in libssh and openssh.

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?

We  confident of the quality of the document as it has been authored
by an implementer, and has been reviewed. 

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.

Bitvise SSH Server, SSH Client, and the FlowSsh library support
curve25519-sha256 as an alias for curve25519-sha256@libssh.org.

OpenSSH Server and Client offer curve25519-sha256 as an alias for
curve25519-sha256@libssh.org.

Personnel

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

Daniel Migault is the Document Shepherd, Eric Rescola is the
Responsible Area Director

(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, provided comments and these have been taken
into account. Comments were mostly editorial. 

(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.

No issues to report.

(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.

All authors have declared 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.

No.

(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? 

No objection has been raised. As the draft is pretty straight forward,
we received few reviews. 

(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.

  Checking references for intended status: Proposed Standard
  ----------------------------------------------------------------------------

    (See RFCs 3967 and 4897 for information about using normative references
    to lower-maturity documents in RFCs)

  ** Downref: Normative reference to an Informational RFC: RFC 6234

  ** Downref: Normative reference to an Informational RFC: RFC 7748

RFC 6234 Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234,
DOI 10.17487/RFC6234, May 2011,
.

RFC 7748 Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
for Security", RFC 7748, DOI 10.17487/RFC7748, January
2016, .

The Downref is justified by RFC3967 as it falls into the following case:
  o  A standards track document may need to refer to a protocol or
      algorithm developed by an external body but modified, adapted, or
      profiled by an IETF informational RFC.


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

No.

(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.

see question 11.

(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.

No.

(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).

(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.

The IANA consideration provides the necessary parameters for the
IANA registries. IANA registries requires IETF consensus. There is
no Expert review.
https://www.iana.org/assignments/ssh-parameters/ssh-parameters.xhtml#ssh-parameters-16

(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.

Not applicable