Re: [AVTCORE] Review of draft-ietf-avtcore-rtp-security-options-04

Colin Perkins <> Thu, 29 August 2013 12:58 UTC

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Date: Thu, 29 Aug 2013 13:57:37 +0100
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Subject: Re: [AVTCORE] Review of draft-ietf-avtcore-rtp-security-options-04
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Thank you for the review. Some comments inline.


On 28 Aug 2013, at 19:32, Alan Johnston <> wrote:
> Here's my review of draft-ietf-avtcore-rtp-security-options-04.
> Summary:  The document is well-written and useful.  There are a few technical issues to resolve but is otherwise ready to progress.
> - Alan -
> Numbers refer to sections in the document.
> 3.1.1:
> It is surprising no mention is made of RFC 4474 in this section (or in the whole document) as DTLS-SRTP keying relies on an integrity protected signaling channel provided by RFC 4474.  When mentioning RFC 4474, it needs to be pointed out that RFC 4474 is effectively being deprecated by the STIR work and has proved to be undeployable and also ineffective for E.164 identities.

I have added a reference to RFC 4474 in Sections 4.1.3 and 4.1.4 as a result of Dan Wing's comments. I'm not familiar with the STIR work, or the other issues, can you suggest text for Section 3.1.1?

> 3.1.5:
> Might be worth a single sentence about what makes ZRTP unique, such as:
>  "ZRTP provides best effort encryption independent of the signaling
> protocol and utilizes key continuity, Short Authentication Strings, or a PKI for authentication."


> 5.1:
> "There also exists a solution that enables the fingerprints to be bound to identities established by the first proxy for each user [RFC4916]."  I don't see how SIP connected identity relates at all to this.  Is this perhaps meant to reference RFC 4474?

Yes, I think so.

> 5.2:
> "But, unless the application and its server is intending to compromise the communication security, they can provide a secure and integrity-protected exchange of the certificate hashes thus preventing any man-in-the-middle (MITM) from inserting itself in the key-exchange."  This is possible, but not trivial, and I doubt few WebRTC signaling channels will provide this. This statement needs some support for it to be included. 

Dan Wing had comments on that section also, and it's been rewritten in the -05 version of the draft. That specific text has been removed, but that's not the only change, and I'd appreciate review to see if the new text makes sense.

> 5.2:
> Might also be worth a mention that ZRTP can be used to verify the
> DTLS-SRTP fingerprints used without relying on any third parties as
> described in draft-johnston-rtcweb-zrtp.

I added a mention of ZRTP here.

> Nits:
> 2:
> "it's" -> "its"
> 2.1:
> "end-points verifiable identity" -> "end-point's verifiable identity"


Colin Perkins