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

Martin Thomson <martin.thomson@gmail.com> Wed, 14 January 2015 22:52 UTC

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From: Martin Thomson <martin.thomson@gmail.com>
To: Simon Perreault <sperreault@jive.com>
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Subject: Re: [rtcweb] Question about srtp_mki in DTLS/SRTP
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On 14 January 2015 at 14:43, Simon Perreault <sperreault@jive.com> wrote:
> 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...

OK, my bad.  Yes, the srtp_mki field in the DTLS handshake is
effectively useless without renegotiation.  If you rekey without
renegotiation, you will need a new scheme for signaling in SRTP proper
when those changes were applied (like Roman's seqno hack).

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