Default value of a session resumption timeout (300 seconds vs 7200 seconds)

[Harish Kulkarni]

Thank you both for bringing this to my attention, your points are
invaluable.

If this is something which gets set from server on client side. can client
override this?. Can i change this to something less and try?. Has anyone
tried?.

Whats the option in openssl.conf or some other place?.

-thanks
harish


On Mon, Jan 25, 2021 at 11:08 PM Matt Caswell <matt at openssl.org> wrote:

>
>
> On 23/01/2021 15:22, John Thoe wrote:
> > Hi list,
> >
> > The session reuse question posted on the mailing list earlier
> > (
> https://mta.openssl.org/pipermail/openssl-users/2021-January/013360.html)
> > reminded of a somewhat similar question I have.
> >
> > As per the docs,
> > https://www.openssl.org/docs/man1.0.2/man3/SSL_get_default_timeout.html,
> > it says the default value is 300 seconds for which a session resuse
> > will be accepted. The docs say that it is the same for all
> > protocols.
> >
> > However I tried it with my setup where I didn't explicitly set the
> > timeout and I am getting 7200 seconds as the default value. s_client
> > output: TLS session ticket lifetime hint: 7200 (seconds). My client
> > openssl.conf has no setting override (not that it should matter
> > because this is a server preference). No OpenSSL settings on the
> > server have been modified as well.
>
> Looks to me like the docs are wrong. They probably should say 7200.
>
>
> >
> > In ssl/ssl_sess.c#L80, the code matches the document: ss->timeout =
> > 60 * 5 + 4;   /* 5 minute timeout by default */ ... (with additional
> > four seconds?)
>
>
> This gets set during construction and then later overwritten when we
> actually get a new session via "ssl_get_new_session":
>
>     /* If the context has a default timeout, use it */
>     if (s->session_ctx->session_timeout == 0)
>         ss->timeout = SSL_get_default_timeout(s);
>     else
>         ss->timeout = s->session_ctx->session_timeout;
>
> In most cases SSL_get_default_timeout() calls tls1_default_timeout() (it
> can end up somewhere different for certain protocol versions - but all
> the different variants are the same!):
>
> long tls1_default_timeout(void)
> {
>     /*
>      * 2 hours, the 24 hours mentioned in the TLSv1 spec is way too long
> for
>      * http, the cache would over fill
>      */
>     return (60 * 60 * 2);
> }
>
> 60 * 60 * 2 = 7200
>
>
> Matt
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mta.openssl.org/pipermail/openssl-users/attachments/20210126/3185bc61/attachment.html>