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Re: [TLS] draft-ietf-tls-tls13-21 posted

Ilari Liusvaara <ilariliusvaara@welho.com> Tue, 04 July 2017 10:50 UTC

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Date: Tue, 04 Jul 2017 13:50:50 +0300
From: Ilari Liusvaara <ilariliusvaara@welho.com>
To: Matt Caswell <frodo@baggins.org>
Cc: "tls@ietf.org" <tls@ietf.org>
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Subject: Re: [TLS] draft-ietf-tls-tls13-21 posted
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On Tue, Jul 04, 2017 at 11:25:35AM +0100, Matt Caswell wrote:
> On 4 July 2017 at 01:01, Eric Rescorla <ekr@rtfm.com> wrote:
> > - Modifying the key derivation for PSKs so that each session ticket
> >   is associated with a distinct PSK.
> 
> Draft-21 says this about the ticket nonce:
> 
>           opaque ticket_nonce<1..255>;
> ...
>    ticket_nonce  A unique per-ticket value.
> 
> 
> Within what context is "uniqueness" required? I am assuming that
> uniqueness within the context of a single TLS connection is all that
> is needed?

Yes, It has to be unique within a connection.

> The nonce can be anything between 1 and 255 bytes long. There is no
> guidance on a suitable length, so I am assuming I can choose anything
> I like as long as the uniqueness constraint is met. OpenSSL
> (currently) only ever issues a single ticket per TLS connection so is
> a single 0 byte sufficient?

Yes, if you only have one ticket per connection, then any legal fixed
value is acceptable.


-Ilari

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