Re: [TLS] 0-RTT and Anti-Replay

Martin Thomson <> Mon, 23 March 2015 03:35 UTC

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Date: Sun, 22 Mar 2015 20:35:34 -0700
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From: Martin Thomson <>
To: Eric Rescorla <>
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Subject: Re: [TLS] 0-RTT and Anti-Replay
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On 22 March 2015 at 20:19, Eric Rescorla <>; wrote:
>> One way to solve this is to say that the server must *fail* 0-RTT, as
>> opposed to fallback to 1-RTT, if the "orbit" indicated in the ClientHello is
>> not that of this server.
> Yeah, this is what I claimed is "implausible" in my original message.
> My concern here is that this basically means that implementations get
> punished with random failures for any data center/routing instabilities...

I don't see any way that we can support a mode that fails with
increased probability like this.  I think that the only real options
here are #2 and #3.  I'm tending toward a requirement for marking the
data as being explicitly replayable, simply because I don't think we
should leave applications with the awkward choice of deciding between
resend and something else.  Mainly because I don't know what that
something else looks like.

For HTTP, I think we can use that first flight for idempotent queries
quite easily and (at worst) the HTTP/2 connection preface.