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Re: [rtcweb] SDP Security Descriptions (RFC 4568) and RTCWeb

Dan Wing <dwing@cisco.com> Tue, 30 April 2013 05:12 UTC

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From: Dan Wing <dwing@cisco.com>
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Date: Mon, 29 Apr 2013 22:12:47 -0700
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To: Iñaki Baz Castillo <ibc@aliax.net>
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Subject: Re: [rtcweb] SDP Security Descriptions (RFC 4568) and RTCWeb
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On Apr 29, 2013, at 4:49 AM, Iñaki Baz Castillo <ibc@aliax.net> wrote:

> 2013/4/29 Tim Panton <tim@phonefromhere.com>:
>> I've seen this asserted more than once, but I'd love to see a _current_ example where
>> you really have an existing network of SRTP/ICE/BUNDLE/RTCP-MUX capable
>> legacy endpoints that you want to connect to webRTC without a media-level SBC or
>> call recording.
>> 
>> My fear is that people are just basing anti-DTLS opinions on the perceived difficulty of
>> building such a network in the future.
>> 
>> I'm ok with legacy interop as a secondary goal of this WG , but putative-future-legacy interop
>> is going too far IMHO, especially since it further complicates the already tricky problem of
>> defining interoperable SDP.
>> 
>> If it is a choice between adding complexity in a legacy gateway or every browser
>> I'd rather add it in the gateway.
> 
> 
> Hi Tim, let's please separate DTLS and DTLS+EKT:
> 
> 
> - DTLS-SRTP:  I agree with you. It seems that people consider it a
> barrier for legacy interop (while it seems not so hard as implementing
> ICE, bundle, rtcp-mix....). Anyhow a media gateway would do the job,
> exactly as when using SDES-SRTP.
> 
> - DTLS-EKT-SRTP:  This requires a gateway sending like "re-INVITE" for
> common operations as multimedia session transfer, which involves the
> gateway becoming both a media gateway and a complex signaling B2BUA
> (and we hate that, right?).

That re-INVITE is necessary because Security Descriptions changed the SRTP key, and Security Descriptions needs to send that re-INVITE.  It is not the fault of DTLS-SRTP-EKT, because it doesn't send a re-INVITE when the SRTP key changes (EKT handles key changes).  

If the objection is the re-INVITE when SRTP keys change, the solution is eliminating Security Descriptions.

-d


> 
> 
> 
> So please let's separate DTLS and DTLS+EKT since they are really
> different options.
> 
> 
> Best regards.
> 
> 
> --
> Iñaki Baz Castillo
> <ibc@aliax.net>
> _______________________________________________
> rtcweb mailing list
> rtcweb@ietf.org
> https://www.ietf.org/mailman/listinfo/rtcweb

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