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Re: [TLS] Resumption Contexts and 0-RTT Finished

Eric Rescorla <ekr@rtfm.com> Tue, 19 July 2016 15:05 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Tue, 19 Jul 2016 16:40:38 +0200
Message-ID: <CABcZeBMsJnmbgMkd=mPRYNZ1nW-inp7Ky0QrjCKyts0iMDhCaA@mail.gmail.com>
To: Ilari Liusvaara <ilariliusvaara@welho.com>
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Subject: Re: [TLS] Resumption Contexts and 0-RTT Finished
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The problem with the second option is that it's not safe to send the 0-RTT
Finished on the wire if you don't know that the other side is 1.3; that's
an assumption we made about 0-RTT but not one we want to make for
PSK-resumption.

-Ekr


On Tue, Jul 19, 2016 at 3:46 PM, Ilari Liusvaara <ilariliusvaara@welho.com>
wrote:

> Thinking about this...
>
> One option would be like 2 on the slides (the overstriked one!), except:
>
> - The message is synthethized, not actually sent on wire (but still
>   logged).
> - It only happens after the last ClientHello.
> - It uses the actual PSK, even if not #0.
>
>
> Maybe I should have listened to the talk more carefully, but the
> reason I got for overstriking the second option was that it is
> unimplementable in practice.
>
>
> Of course, dunno if the changes would actually fix the problems
> with PSK contexts...
>
>
>
> -Ilari
>
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