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Re: [MMUSIC] draft-dtls-sdp: Allow offerer to establish DTLS association before it has received the SDP answer?

Martin Thomson <martin.thomson@gmail.com> Tue, 23 May 2017 10:26 UTC

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From: Martin Thomson <martin.thomson@gmail.com>
Date: Tue, 23 May 2017 20:25:57 +1000
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To: Christer Holmberg <christer.holmberg@ericsson.com>
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Subject: Re: [MMUSIC] draft-dtls-sdp: Allow offerer to establish DTLS association before it has received the SDP answer?
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On 23 May 2017 at 20:15, Christer Holmberg
<christer.holmberg@ericsson.com> wrote:
> But, what about data received before the completion is received?

Well, I'd prefer to drop that, because buffering is tricky, but as I
said, holding it without even decrypting it could work.

Note that many DTLS-SRTP implementations won't even allow you to call
the exporter until the handshake is complete.  In order to even get
the data to arrive you have to do some inadvisable things to the
stack, such as accepting the peer's certificate, then you have to kill
the connection when the a=fingerprint arrives and doesn't match.  It's
much easier to validate inline.

> Also, if I understand the FEDEX use-case, not only would you have to be
> able to receive media - if you are e.g., going to provide DTMFs you could
> also have to SEND data? Or?

Yeah, sending DTMF to who-knows isn't a good idea.  I'm not clear on
whether sending DTMF is part of the arrangement.  Sounds like a great
way to avoid tarriffs altogether; I'm surprised that service providers
would even allow that.

This is why I think that this "unverified media" is the wrong solution
here.  It's not impossible to have an authenticated session and
accomplish these goals.

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