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Re: [TLS] 0RTT and HelloRetryRequest (Re: Narrowing the replay window)

Eric Rescorla <ekr@rtfm.com> Wed, 30 March 2016 22:59 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Wed, 30 Mar 2016 15:59:08 -0700
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To: Martin Thomson <martin.thomson@gmail.com>
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Subject: Re: [TLS] 0RTT and HelloRetryRequest (Re: Narrowing the replay window)
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On Wed, Mar 30, 2016 at 3:57 PM, Martin Thomson <martin.thomson@gmail.com>
wrote:

> On 31 Mar 2016 5:56 AM, "Ilari Liusvaara" <ilariliusvaara@welho.com>
> wrote:
> > Then on topic of 0-RTT, how does 0-RTT key hashes behave if
> > handshake is restarted (main handshake hash continues, but
> > 0-RTT hash context currently needs to be separate from the
> > main context)?
>
> Good question. I don't recall that being discussed. I see three options :
>
> 1. Continue the hash, just like in 1-RTT
>
> 2. Treat HelloRetryRequest as a denial of the entire first flight.
>
> 3. Signal the choice.
>
> Option 2 suits best if we consider HelloRetryRequest to be a DoS feature
> exclusively or at least primarily. But we have other reasons for it and I
> don't think that DoS mitigation is a big factor for TCP.
>

I believe Option #2 is simplest.

-Ekr

I think that option 1 is easy enough, since both sides have to extend the
> hash in any case. 3 is just complexity.
>
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