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Re: [tram] Stephen Farrell's Discuss on draft-ietf-tram-turn-third-party-authz-13: (with DISCUSS and COMMENT)

"Salz, Rich" <rsalz@akamai.com> Wed, 22 April 2015 17:14 UTC

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From: "Salz, Rich" <rsalz@akamai.com>
To: Spencer Dawkins at IETF <spencerdawkins.ietf@gmail.com>
Thread-Topic: [tram] Stephen Farrell's Discuss on draft-ietf-tram-turn-third-party-authz-13: (with DISCUSS and COMMENT)
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Date: Wed, 22 Apr 2015 17:13:42 +0000
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Cc: "tram-chairs@ietf.org" <tram-chairs@ietf.org>, "tram@ietf.org" <tram@ietf.org>, "rlb@ipv.sx" <rlb@ipv.sx>, "Tirumaleswar Reddy (tireddy)" <tireddy@cisco.com>, "Williams, Brandon" <bowill@akamai.com>, Martin Thomson <martin.thomson@gmail.com>, "Stephen Farrell (stephen.farrell@cs.tcd.ie)" <stephen.farrell@cs.tcd.ie>
Subject: Re: [tram] Stephen Farrell's Discuss on draft-ietf-tram-turn-third-party-authz-13: (with DISCUSS and COMMENT)
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> but could you explain to me (I'm thinking like a sentence, not like a thesis) on why those concerns don't apply?

Sure.  First, look at https://tools.ietf.org/html/rfc6194#section-3  and quote that :)

Second, this is not being used as a public signature mechanism, but as a private key for an HMAC.  So you can't modify "original content" to find a collision since you don't have the content, and more importantly, you don't have the digest value for which the attacker is trying to find a collision.

Hope that helps.

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