Re: [rtcweb] Stephen Farrell's Discuss on draft-ietf-rtcweb-stun-consent-freshness-15: (with DISCUSS and COMMENT)

[Muthu Arul Mozhi Perumal <[e-mail]>]

Hi Stephen,

On Thu, Aug 6, 2015 at 4:08 AM, Stephen Farrell <[e-mail]>
wrote:

> Stephen Farrell has entered the following ballot position for
> draft-ietf-rtcweb-stun-consent-freshness-15: Discuss
>
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> Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html
> for more information about IESG DISCUSS and COMMENT positions.
>
>
> The document, along with other ballot positions, can be found here:
> https://datatracker.ietf.org/doc/draft-ietf-rtcweb-stun-consent-freshness/
>
>
>
> ----------------------------------------------------------------------
> DISCUSS:
> ----------------------------------------------------------------------
>
>
>
> Apologies that these discuss points are maybe asking
> fairly fundamental questions.  That could be that this
> is really the first of the new security things required
> by rtcweb to get to the IESG.  Or maybe I'm misreading
> stuff here, if so, sorry;-)
>
> (1) Why call this "consent?" That term is (ab)used in
> many ways on the web, and adding another variation
> without a definition that distinguishes this from "click
> ok to my 200 page anti-privacy policy" or "remember that
> example.com is allowed use my camera/mic" seems like a
> terrible idea. I also don't see how this can ever be
> something to which a normal person can "consent" (i.e.
> consciously agree while fully understanding) so the term
> is IMO very misleading, and will I fear be used to
> mislead further.  (See also some of the comments below -
> I do not think we ought be as fast and loose with this
> aleady terribly badly used term.) To summarise: I'd love
> if you did s/consent/anything-else/g but if not, please
> define consent here in a way that clearly and
> unambiguously distinguishes this usage from other abuses
> of the term.
>

​The document already has a clear and unambiguous definition of the term,
IMHO: ​

​   Consent:  The mechanism of obtaining permission from the remote
      endpoint to send non-ICE traffic to a remote transport address.
      Consent is obtained using ICE.​

​Is that definition lacking something? ​I think finding an alter term would
be as hard as finding an alternate term for 'attack' as used in several
RFCs [attack being (ab)used in many contexts, including in heart attack ;)]


>
> (2) WebRTC does not require STUN or TURN servers for
> some calls, even if it does for many. Why is it ok to
> require such a server be present in all calls (which I
> think this means) espcially when that means exposing
> additional meta-data (calling parties in a case where
> the servers weren't needed and call duration in all
> cases) to those servers when that is not always
> necessary?
>

​That looks a misunderstanding. Consent freshness doesn't require such
server's to be present. Please point out to the text leading to the
misunderstanding.


>
> (3) (end of p5) You have a MUST NOT here that is
> depenedent on current browser implementations. Why is
> that an IETF thing and not a W3C thing? But more
> interestingly, can one securely use this protocol
> without the kind of JS vs. browser sandboxing etc that's
> needed in the web?


​Yes, the mechanism has the same security properties within and outside the
WebRTC sandboxing.


> If the answer is "no" then don't you
> need to say that this protocol can only safely be used
> for such implementations? (In section 2, which almost
> but not quite says that.)
>

​Section 2 doesn't say that. It only says WebRTC is the primary use case
for the mechanism at the moment and future use cases based on similar
sandboxing models can make use of it.


>
> (4) Cleared.
>
> (5) Cleared.
>
>
> ----------------------------------------------------------------------
> COMMENT:
> ----------------------------------------------------------------------
>
>
> (Was discuss point#4)
> "Section 8: Where are these 96 bits defined? I think
> this "requires..." statement needs a precise reference
> to the place in some ICE/TURN/STUN RFC where it's
> defined. (And I forget where that is, sorry:-) This
> should be an easy fix."
> Alissa gave me the reference [1] sothat's grand. It
> might be an idea to make that clearer if it wasn't
> just me missing it as I read, which is very possible;-)
>
> [1] https://tools.ietf.org/html/rfc5389#section-6
>
> - abstract: why is only sending "media" mentioned here?
> What about data channels?  And the body of the document
> in fact says this all applies to any non-ICE data and
> not only media.
>

​Agree, that should be "traffic".


>
> - intro: "initial consent to send by performing STUN" I
> do not find the word consent in either rfc5245 or 3489,
> but perhaps it is used somewhere else. Where?  And with
> what meaning?
>

​Consent is a new usage of STUN and is described in
draft-ietf-rtcweb-security-arch, draft-ietf-rtcweb-security and in this
document.


>
> - section 4, 2nd last para - I think the conclusion is
> bogus.  An implementation knows when the keying it's
> using can not involve >1 (nominally operating) party.
>

That paragraph is here:

​​   When Secure Real-time Transport Protocol (SRTP) is used, the
   following considerations are applicable.  SRTP is encrypted and
   authenticated with symmetric keys; that is, both sender and receiver
   know the keys.  With two party sessions, receipt of an authenticated
   packet from the single remote party is a strong assurance the packet
   came from that party.  However, when a session involves more than two
   parties, all of whom know each other's keys, any of those parties
   could have sent (or spoofed) the packet.  Such shared key
   distributions are possible with some MIKEY [RFC3830] modes, Security
   Descriptions [RFC4568], and EKT [I-D.ietf-avtcore-srtp-ekt].  Thus,
   in such shared keying distributions, receipt of an authenticated SRTP
   packet is not sufficient to verify consent.

​I'll defer it to someone who has more knowledge that me on shared key
distribution..


>
> - 5.1, 3rd para: "Explicit consent to send is
> obtained..." is misleading. That is not a concept that
> an implementation of STUN will embody.
>

​As said earlier, consent is a new STUN usage. How would the following?

    An endpoint that implements this specification obtains and maintains
    consent to send by sending STUN binding request...


>
> - 5.1, What is the "Note" about TCP for? Why is this
> needed?
>

​It is needed because WebRTC data traffic sent over TCP could get converted
to UDP by TURN servers. It is somewhat similar to why we need application
layer security when traffic is sent over IPSec. The later may not be
end-to-end.

Muthu