Re: [TLS] Earlier exporters

Eric Rescorla <ekr@rtfm.com> Fri, 07 October 2016 21:07 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Fri, 7 Oct 2016 14:07:09 -0700
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To: Nick Harper <nharper@google.com>
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Cc: "tls@ietf.org" <tls@ietf.org>
Subject: Re: [TLS] Earlier exporters
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I was assuming that there were two exporters:

Export() --> the same API as in 1.2 and computed as described here
Export0RTT -> A new API that computes the early_exporter.


-Ekr

On Fri, Oct 7, 2016 at 1:59 PM, Nick Harper <nharper@google.com>; wrote:

> Does the wording of this PR mean that the value from the exporter changes
> depending on whether it's run before or after exporter_secret can be
> computed? I think it would be better to keep an RFC 5705-style exporter
> that remains constant for the connection. The 0-RTT exporter from an API
> perspective can be a separate thing that a caller has to explicitly choose
> to use.
>
> On Fri, Oct 7, 2016 at 8:10 AM, Eric Rescorla <ekr@rtfm.com>; wrote:
>
>> Please see the following PR:
>>   https://github.com/tlswg/tls13-spec/pull/673
>>
>> This includes various changes to make exporters/resumption work better.
>>
>> Basically:
>> 1. Add a 0-RTT exporter and change the transcript for the regular
>> exporter so it
>>     only includes the transcript up to ServerFinished. This gives it
>> parity with the
>>     rest of the traffic keys. If we need an exporter with the full
>> transcript we can
>>     always add it later
>>
>> 2. Point out that you can predict ClientFinished for NST when not doing
>>     Client auth. This lets you issue tickets on the server's first
>> flight, while still
>>     ensuring that if you do client auth you still bind resumption to the
>> client's
>>     full transcript.
>>
>> These are pretty straightforward changes, so absent objections I'll merge
>> them early next week.
>>
>> -Ekr
>>
>>
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>