Re: [TLS] 0-RTT (Was: Re: 0-RTT and Anti-Replay)

Ilari Liusvaara <ilari.liusvaara@elisanet.fi> Thu, 14 May 2015 06:09 UTC

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Date: Thu, 14 May 2015 09:08:59 +0300
From: Ilari Liusvaara <ilari.liusvaara@elisanet.fi>
To: Martin Thomson <martin.thomson@gmail.com>
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Subject: Re: [TLS] 0-RTT (Was: Re: 0-RTT and Anti-Replay)
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On Wed, May 13, 2015 at 02:18:59PM -0700, Martin Thomson wrote:
> On 13 May 2015 at 13:58, Ilari Liusvaara <ilari.liusvaara@elisanet.fi>; wrote:
> > Suppose that client is willing to accept multiple of the three key
> > exchange types (full-DHE, abbrevated and pure-PSK) at once. Now,
> > all three are expected to use different keys. Under what keys does
> > client encipher the 0RTT data?
> 
> 
> Why wouldn't the client just choose and signal the option they chose?

Just one allowed, or multiple (server picks one)? :-)
 
> BTW, it has been suggested that there might need to be some material
> from the server contributed to this mix to prevent an unknown key
> share attack.  So secret[x] + ClientRandom is not quite sufficient.

Any specifics?

Is this somehow related to attack that arises if client does not do
Proof-of-Possession of the 0-RTT key[1]?


[1] AFAIK, one way to do that PoP is to mix the key (or closely
related value) into appMS if 0-RTT is accepted.


-Ilari