Re: [rtcweb] Asking TLS for help with media isolation

Watson Ladd <> Fri, 04 April 2014 02:49 UTC

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Date: Thu, 03 Apr 2014 19:49:33 -0700
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From: Watson Ladd <>
To: Bernard Aboba <>
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Subject: Re: [rtcweb] Asking TLS for help with media isolation
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On Thu, Apr 3, 2014 at 7:29 PM, Bernard Aboba <> wrote:
> Martin said:
> "I have pointed to draft-thomson-tls-acp as a potential solution here,
> but others have noted that ALPN tokens could be used."
> Watson said:
> "Putting on my TLS hat, TLS already lets you send data across the
> network securely. Why does this bit need to be treated differently
> from all others?
> [BA] As Martin indicates, the desire for isolation needs to be communicated
> to ensure that remote media is not misused.  With either of the TLS
> approaches that Martin has suggested,  the desire for isolation is
> communicated directly between the peers.   Having this occur E2E via media,
> not hop-by-hop via signaling avoids the risk of a MITM preventing isolation
> from being negotiated.

The MITM can kill any TLS connection containing the extension. My
understanding is that signalling data is immutable, hence the need to
ask the browser to generate it.

> However once the desire for isolation is communicated E2E (either via ACP or
> ALPN tokens), there is nothing in the SRTP traffic (keyed by DTLS/SRTP) that
> indicates that the traffic is to be isolated.

I don't see why the isolation status cannot be included as an
extension to SRTP. You aren't asking TLS to make extensions for video
resolution and codec after all.

Watson Ladd

"Those who would give up Essential Liberty to purchase a little
Temporary Safety deserve neither  Liberty nor Safety."
-- Benjamin Franklin