Re: [TLS] draft-ietf-tls-tls13-15

Eric Rescorla <ekr@rtfm.com> Thu, 18 August 2016 12:33 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Thu, 18 Aug 2016 05:29:34 -0700
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To: Ilari Liusvaara <ilariliusvaara@welho.com>
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Subject: Re: [TLS] draft-ietf-tls-tls13-15
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Thanks for the quick review.

On Wed, Aug 17, 2016 at 10:26 PM, Ilari Liusvaara <ilariliusvaara@welho.com>
wrote:

> On Wed, Aug 17, 2016 at 02:49:52PM -0700, Eric Rescorla wrote:
> > Folks,
> >
> > I've just submitted draft-ietf-tls-tls13-15.
>
> Doing brief review:
>
> - Section 4.2.2 talks EdDSA using "ECDSA cipher suites". TLS 1.3 does
>   not have those. However, this kind of information is very relevant
>   for TLS 1.2 backward compatiblity: you need to assign TLS 1.2
>   cipher suites for EdDSA in order to use it in TLS 1.2. TLS 1.3 does
>   not care either way.
>

Thanks. Will try to fix.


- I note that accepting PSK and selecting the auth mode seem to be
>   in separate messages, which seems quite annoying implementation-
>   wise..


Can you elaborate on this? The intend is that they both appear in
ServerHello
(in pre_shared_key and signature_algorithms respectively).


- Can the server send arbitrary certificate in response to PSK or is
>   it somehow restricted? The document does not seem to talk about it.
>

The document right now is supposed to be PSK XOR server signs, so the
answer is supposed to be "no". If/when we allow both together, then
we'll have to address this, which is a bit tricky.



>
> - The HelloRetryRequest is problematic in pure-PSK case[1].
>
>
> [1] One way to do it would be to move the group to extension, which
> would only be sent if new group was needed. Then one could always
> require at least one extension (the field could also be renamed).
> Also, one could make it so that HRR extensions don't have to
> correspond to CH extensions (and unsupported one is a fatal error).
>

Agreed on both counts. PR wanted.
https://github.com/tlswg/tls13-spec/issues/560

-Ekr


>
>
>
> -Ilari
>