Getting SSL_SESSION remaining lifetime

[Benjamin Kaduk]

On Thu, Sep 16, 2021 at 04:57:03PM +0200, Hubert Kario wrote:
> On Thursday, 16 September 2021 16:28:47 CEST, Benjamin Kaduk wrote:
> > On Thu, Sep 16, 2021 at 04:11:49PM +0200, Hubert Kario wrote:
> > > On Thursday, 16 September 2021 04:41:44 CEST, Jaya Muthiah wrote:
> > > > 
> > > > I am trying to get the remaining lifetime of the ticket so that server
> > > > can decide to renew ticket or not
> > > 
> > > TLS 1.3 tickets are single use. If the ticket was used by a client, and
> > > you expect it to make a connection in the future, server needs to
> > > send a new
> > > one.
> > 
> > Single-use tickets are only a protocol requirement when 0-RTT data is used.
> > The OpenSSL implementation even allows the libssl-internal enforcement of
> > single-use to be disabled (see SSL_OP_NO_ANTI_REPLAY at
> > https://urldefense.com/v3/__https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_options.html__;!!GjvTz_vk!GxR4URFTB0lwkM5nlYZdtn3DUdeaujsu1sHMYc_nRTUpkmLQP8-zz_b4HS_rcA$ ).
> > OpenSSL as a client also has some measures to encourate single-use tickets,
> > which I have a PR open to provide a knob to disable:
> > https://urldefense.com/v3/__https://github.com/openssl/openssl/pull/16598__;!!GjvTz_vk!GxR4URFTB0lwkM5nlYZdtn3DUdeaujsu1sHMYc_nRTUpkmLQP8-zz_YPrcg6yw$  .
> 
> They're single use not only because of replay but also because of privacy
> reasons, as reuse of a ticket indicates that the same client did send it.

Yes.
But the protocol itself only encourages single-use for privacy reasons.
The protocol does not *require* single-use in that case.

-Ben