Default value of a session resumption timeout (300 seconds vs 7200 seconds)
matt at openssl.org
Wed Jan 27 10:02:57 UTC 2021
On 26/01/2021 18:13, Harish Kulkarni wrote:
> Thank you both for bringing this to my attention, your points are
> 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?.
The session timeout is something entirely controlled by the server. The
client has no influence on this*. If the server is using session tickets
for its sessions then it provides a lifetime hint to the client to say
how long the client can expect the session to be good for. The client
can query this using SSL_SESSION_get_ticket_lifetime_hint().
On the server the timeout can be configured using SSL_CTX_set_timeout().
I don't think this is possible to change via openssl.conf.
* Note that the client may be managing a cache of sessions provided by
servers. That's not something that happens by default in OpenSSL but can
be configured using SSL_CTX_set_session_cache_mode(). In that case there
will be separate timeouts associated with the life of the session in the
client cache. Those timeouts may not be the same as the server's timeouts.
> On Mon, Jan 25, 2021 at 11:08 PM Matt Caswell <matt at openssl.org
> <mailto: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
> > reminded of a somewhat similar question I have.
> > As per the docs,
> > 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);
> 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
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