Re: [rtcweb] Question about srtp_mki in DTLS/SRTP

Simon Perreault <sperreault@jive.com> Wed, 14 January 2015 22:43 UTC

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Date: Wed, 14 Jan 2015 17:43:27 -0500
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From: Simon Perreault <sperreault@jive.com>
To: Martin Thomson <martin.thomson@gmail.com>
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Subject: Re: [rtcweb] Question about srtp_mki in DTLS/SRTP
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On Wed, Jan 14, 2015 at 4:49 PM, Martin Thomson <martin.thomson@gmail.com>
wrote:

> > use_srtp is in ClientHello, and that's renegotiation, right? If so, can
> you
> > end up with new keys without a new MKI?
>
> The use_srtp extension really only allows the peers to negotiate which
> SRTP cipher they want to use, it doesn't really establish the keys.
> That's the role of the exporter.


Ok.... but I think you may have missed my point. My point is that srtp_mki,
being part of use_srtp, only gets renewed upon renegotiation. So if you
just export new keying material without renegotiating, you don't have a new
MKI for those new keys you just exported. So removing renegotiation
effectively makes srtp_mki useless. Unless I misunderstand the difference
between renegotiation and rekey...

Simon