[openssl-users] Session Ticket Support in Openssl TLS 1.2

[Benjamin Kaduk]

On 06/16/2017 01:58 PM, Neetish Pathak wrote:
> Hello 
> Thanks
> I tried reading  some content from the server side and I observed the
> new_session_cb getting invoked in that case on the client side. I
> understand that may be due to delayed NewSession info transfer from
> server side to client side. But it is helpful for saving the session
> info on the client side. (Thanks Matt for your input)
>
> However, now I have two concerns
>
> 1) I see that latency for handshake with session resumption in TLS 1.3
> has not improved as much as it improves for TLS 1.2
> With TLS 1.3, I observed that resumption brings down the connection
> time from 2.5 ms to 1.2-1.3 ms
> while with TLS 1.2 (using either session IDs or tickets), the
> connection time reduces from 2.5 ms to 0.5-0.6 ms.
>
> The whole code is similar for running the two experiments with only
> max TLS version changed. Can someone comment on the latency
> measurements for the two cases.
> TLS 1.3 is supposed to be better than TLS 1.2 in my opinion. Please
> comment.
>

Are you seeing a HelloRetryRequest in the resumption flow?  That would
add an additional round trip.  (Your numbers in milliseconds are of
course not transferrable to other systems; round-trips is an easier to
understand number.)  RFC 5246 and draft-ietf-tls-tls13-20 both have
message-flow diagrams that show the number of round trips in various
handshake flows.

> 2) PSK (Pre-shared keys) for resumption are highly emphasized in TLS
> 1.3 RFC. How do we generate pre-shared keys in advance even without
> making the first connection. Can someone guide me in the right direction.
>

The security properties of such "external" PSKs are substantially
different than the "ephemeral" PSKs used in resumption flows.  I do not
think I can recommend their use in the general case when resumption
flows are available.
Regardless, external PSK support is still a work in progress:
https://github.com/openssl/openssl/pull/3670

-Ben
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