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

Roman Shpount <roman@telurix.com> Wed, 14 January 2015 17:43 UTC

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Date: Wed, 14 Jan 2015 12:43:14 -0500
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From: Roman Shpount <roman@telurix.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 12:26 PM, Martin Thomson <martin.thomson@gmail.com>
wrote:

> On 14 January 2015 at 08:34, Simon Perreault <sperreault@jive.com> wrote:
> > Without an MKI, when packets arrive you have to try to authenticate them
> > with the newest key, and if that doesn't work try progressively older
> keys.
> > It's a hassle: you have to store keys in chronological order and iterate.
>
> Yes, SRTP doesn't carry the epoch and trial decryption sucks, so the
> MKI is quite attractive... if you rekey.  However, as it stands, very
> few implementations will permit a DTLS re-handshake.  Firefox and
> Chrome actively disable renegotiation (desktop Chrome anyway, I'm not
> 100% on the BoringSSL-based versions, like Android).
>
>
You can handle the key transition based on the SRTP sequence numbers. Not
the greatest thing but it does work. BoringSSL versions do not support
renegotiation either.
_____________
Roman Shpount

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