[openssl-users] session resumption tls1.2/tls1.3

Matt Caswell matt at openssl.org
Fri Jul 14 09:54:52 UTC 2017

On 13/07/17 23:52, Neetish Pathak wrote:
> Hi All,
> Help with these queries please,
> 1) Is it possible to use external session files (with session info as
> identifiers or tickets for out of band resumption) for session
> resumption in TLS 1.2. Does it need some kind of callback like the way
> it is used in TLS 1.3  with (SSL_set_psk_find_session_callback) /
> SSL_set_psk_use_session_callback

I'm not entirely clear what you're asking here. The callbacks you
mention are for setting up an external PSK in TLSv1.3. In TLSv1.3 we use
an SSL_SESSION object to encapsulate the PSK details. This is different
to session resumption, where the server sends the session details in a
NewSessionTicket message in one connection, so that we can "resume" it
in a later connection.

So if your question is really "can you external session files for PSK in
TLSv1.2" then the answer is no. PSK works completely differently in TLSv1.2.

> 2) In TLS 1.3, is early data not enabled for out of band PSK session
> resumption. Is it only possible with in-band session resumption. 
> SSL_write_early_data always fails when I load a session from a session
> file to perform external PSK resumption before sending the session data.
> For in-band resumption it succeeds.

Currently we only support early-data for ticket based resumption. You
cannot do it with an external PSK. However this PR (which is currently
going through review) will add that capability:



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