Connection-Oriented Media Transport over the Transport Layer Security (TLS) Protocol in the Session Description Protocol (SDP)
draft-ietf-mmusic-4572-update-13

[Ballot comment]
Section 5.1 says:

"An endpoint MAY, in addition to its more preferred hash function,
  also verify that each certificate used matches fingerprints
  calculated using other hash functions.  Unless there is a matching
  fingerprint for each tested hash function, the endpoint MUST NOT
  establish the TLS connection."

This seems a little weird to me. It's up to the endpoint to decide whether to check for errors, and then if it does find an error it can't setup the connection, whereas if it just hadn't checked it would be able to setup the connection. I think it would help to explain why an endpoint would be motivated to check multiple fingerprints.

[Ballot comment]

I had two (or 4 depending how you count:-) things
I'd like to check here. They were pretty easy to
handle. (We more or less resolved this by mail.)

(1) section 5: I'm wondering if we have the right
set of hash functions here. Deprecating md2 and md5
is great, but I have a bunch of questions about the
others:

(1.1) why not also say that sha-1 MUST NOT be used
for new things (or similar)?

(1.2) do you really need sha-224 and 384? I think
nobody uses those at all.

(1.3) I'm a bit surprised you didn't add sha3 (and
maybe remove sha-512 if that's not needed) Even if
you don't encourage use of sha3, it might be good
to include it in the abnf now in case it gets
popular.

(2) Wouldn't it be a good plan to say that TLS
as-used MUST conform to BCP195? If not, why not?

[Ballot discuss]

I've two (or 4 depending how you count:-) things
I'd like to check here. Should be pretty easy to
handle.

(1) section 5: I'm wondering if we have the right
set of hash functions here. Deprecating md2 and md5
is great, but I have a bunch of questions about the
others:

(1.1) why not also say that sha-1 MUST NOT be used
for new things (or similar)?

(1.2) do you really need sha-224 and 384? I think
nobody uses those at all.

(1.3) I'm a bit surprised you didn't add sha3 (and
maybe remove sha-512 if that's not needed) Even if
you don't encourage use of sha3, it might be good
to include it in the abnf now in case it gets
popular.

(2) Wouldn't it be a good plan to say that TLS
as-used MUST conform to BCP195? If not, why not?

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

The IANA Services Operator has completed its review of draft-ietf-mmusic-4572-update-11.txt. If any part of this review is inaccurate, please let us know.

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

The current document updates RFC4572 and we are aware of three references that should be updated from RFC4572 to [ RFC-to-be ].

They are:

SDP Name TCP/TLS in the protoco subregistry of the Session Description Protocol (SDP) Parameters registry located at:

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

The SDP session and media-level attributes: 'fingerprint' located in the att-field (both session and media level) subregistry also in the Session Description Protocol (SDP) Parameters registry located at:

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

And, finally, the Hash Function Textual Names registry located on the IANA Protocol Registries Matrix located at:

https://www.iana.org/protocols

The IANA Services 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 only to confirm what actions will be performed.

Thank you,

Sabrina Tanamal
IANA Services Specialist
PTI

The following Last Call announcement was sent out:

From: The IESG
To: "IETF-Announce"
CC: ben@nostrum.com, mmusic@ietf.org, mmusic-chairs@ietf.org, fandreas@cisco.com, "Flemming Andreasen" , draft-ietf-mmusic-4572-update@ietf.org
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (Connection-Oriented Media Transport over TLS in SDP) to Proposed Standard


The IESG has received a request from the Multiparty Multimedia Session
Control WG (mmusic) to consider the following document:
- 'Connection-Oriented Media Transport over TLS in SDP'
  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 2017-01-26. 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 specifies how to establish secure connection-oriented
  media transport sessions over the Transport Layer Security (TLS)
  protocol using the Session Description Protocol (SDP).  It defines a
  new SDP protocol identifier, 'TCP/TLS'.  It also defines the syntax
  and semantics for an SDP 'fingerprint' attribute that identifies the
  certificate that will be presented for the TLS session.  This
  mechanism allows media transport over TLS connections to be
  established securely, so long as the integrity of session
  descriptions is assured.

  This document obsoletes RFC 4572, by clarifying the usage of multiple
  fingerprints.




The file can be obtained via
https://datatracker.ietf.org/doc/draft-ietf-mmusic-4572-update/

IESG discussion can be tracked via
https://datatracker.ietf.org/doc/draft-ietf-mmusic-4572-update/ballot/


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

This is my AD evaluation of draft-ietf-mmusic-4572-update-10. Overall it's in good shape, but there are a couple of issues that I think need to be addressed prior to IETF last call. I also have some minor and editorial comments that can be addressed along with any last call feedback.

I realize this is in effect a "bis" draft, and I've mostly confined my comments to new text. However, I have a few comments where something from the original text may be out of date or cause confusion related to the changes.

-----------------------


Major Comments (To be addressed before IETF LC:

-5.0, 2nd to last paragraph:
What does "MUST NOT use" mean? MUST NOT generate? MUST NOT verify? Both?

-5.1, 2nd to last paragraph:
This paragraph confusing to me. The first part says you MUST NOT establish the TLS connection if the most secure hash fails to match, but then it goes on to say you MAY check other hashes. If the most secure hash must match, what's the point in checking others? Or is the "MUST NOT establish" part incorrect? Or is it saying you can optionally require a hash to match for every included hash function? (If the latter is true, then a note why you might want to do that might be helpful.)

It think it would help to cast this paragraph as a stepwise procedure for matching certificates.


Minor Comments:

-3.2, last paragraph: Is s/mime still a reasonable example, given that no one does it? Would it make sense to cite 4474/4474bis instead or in addition?

- 3.4, example: Perhaps the example should use the newly recommended hash function? Maybe illustrate multiple fingerprints?

-5.1, last paragraph: I understand this to say that if I have multiple certificates and multiple fingerprints, I have to potentially compare every fingerprint against every cert to figure out which go with which? Is that really the intent?

-7, paragraphs 4 and 6. (I think this is old text, but it's confusing enough that it might be worth addressing.) Paragraph 4 says "Users SHOUD NOT, in any circumstances be notified about certificates...sent over an integrity protected channel". But paragraph 6 says that the user SHOULD be notified when the cert identity differs from the SIP signaled identity, even when self-signed certs are used. Nothing there suggests that integrity protection removes the need to notify. Should it?

-7, paragraph 7: "The group consensus was to wait until a
  use-case requiring secure connection-oriented RTP was presented"

Is that still true?


Editorial comments and nits:

- 1, 2nd paragraph: "... channel t provides confidentiality..."
s/t/that

- 1, last paragraph: Please consider putting this in a separate "changes since..." section. While the information is here, someone wanting to quickly find the changes would appreciate them showing up in the ToC.

Also, when using non-mnemonic citation anchors, please do not treat the citation as a word in the sentence. For example, "obsoletes RFC 4572 [21]" and "obsoletes [RFC4572]" are both acceptable, but "obsoletes [21]" is reader-unfriendly.

-5.0, 2nd to last paragraph:
Should "cipher suites" be "hash functions"?

-5.1, 2nd to last paragraph:  "MUST be able to" uses the 2119 keyword to describe the condition, not the action. It would be more correct to say something like "MUST NOT establish the connection unless it can match at least one fingerprint."  (Yes, I know this is pedantic.)

-6.2, 2nd paragraph: "...certificate does not match the provided fingerprint"
Should that now say "does not match _a_ provided fingerprint"?

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?

Proposed Standard, which is appropriate since the document obsoletes RFC 4572. The title page shows the proper status. 

(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

The document specifies how to establish secure connection-oriented media transport sessions over the Transport Layer Security (TLS) protocol using the Session Description Protocol (SDP).  It defines a new SDP protocol identifier, 'TCP/TLS'.  It also defines the syntax and semantics for an SDP 'fingerprint' attribute that identifies the certificate that will be presented for the TLS session.  This mechanism allows media transport over TLS connections to be established securely, so long as the integrity of session descriptions is assured.

This document obsoletes RFC 4572 but remains backwards compatible with older implementations.  The changes from RFC 4572 are that it clarifies that multiple 'fingerprint' attributes can be used to carry fingerprints, calculated using different hash functions, associated with a given certificate, and to carry fingerprints associated with multiple certificates.  The fingerprint matching procedure, when  multiple fingerprints are provided, are also clarified.  The document also updates the preferred cipher suite with a stronger cipher suite, and removes the requirement to use the same hash function for calculating a certificate fingerprint and certificate signature.



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 was adopted as a WG document in April 2016 and hence has progressed fairly quickly. WG adoption was based on strong consensus and a clear need; the document has subsequently seen good WG discussion. The document started out as an update to RFC 4572, but was more recently changed to obsolete RFC 4572 after some concerns were raised. The resulting document has solid consensus in the WG.


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?

There are various implementations of the existing RFC 4572. The new specification is needed for RTCWeb and hence several vendors are expected to implement it.

There were many individuals providing valuable input, however Martin Thomson and Roman Shpount in particular deserve special mention.


Personnel

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

Flemming Andreasen is the Document Shepherd and Ben Campbell is the Responsible 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 have reviewed the current and several earlier versions of the document, including Nits checks.

Note that the first line on Page 3 contains two typos that should be corrected during the publication process (change "TLS to "The TLS" and "channel t" to "channel that")

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

No concerns. The changes to RFC 4572 are the result of extensive discussion in the WG.

(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.

N/A


(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 such 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.

Confirmed

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

No IPR disclosure

(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 document has received substantial discussion from several people and the WG consensus is solid at this point.


(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.)

N/A

(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 document normatively references a NIST specification (FIPS 180-2) and an ITU-T Recommendation (X.509) which causes two "possible down-ref" comments. Both of these references are needed and were also present in the original RFC 4572. 

The IP examples use IPv4 only, which seems reasonable since the document does not contain any IP version specific mechanisms or considerations.


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

N/A

(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?

N/A

(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.

There are two downward references (as noted above):

  [1]    National Institute of Standards and Technology, "Secure
              Hash Standard", FIPS PUB 180-2, August 2002,
              .

  [2]    International Telecommunications Union, "Information
              technology - Open Systems Interconnection - The Directory:
              Public-key and attribute certificate frameworks",
              ITU-T Recommendation X.509, ISO Standard 9594-8, March
              2000.


(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.

The document obsoletes RFC 4572, as indicated on the title page and explained in both the 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).

Confirmed (N/A)

(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.

N/A

(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.

The ABNF has been verified with Bill Fenner's ABNF parser.