SSL_CTX_set_session_cache_modOpenSSL_CTX_set_session_cache_mode(3)

NAME    [Toc]    [Back]

       SSL_CTX_set_session_cache_mode, SSL_CTX_get_session_cache_mode
 - enable/disable session caching

LIBRARY    [Toc]    [Back]

       libcrypto, -lcrypto

SYNOPSIS    [Toc]    [Back]

        #include <openssl/ssl.h>

        long SSL_CTX_set_session_cache_mode(SSL_CTX ctx, long mode);
        long SSL_CTX_get_session_cache_mode(SSL_CTX ctx);

DESCRIPTION    [Toc]    [Back]

       SSL_CTX_set_session_cache_mode() enables/disables session
       caching by setting the operational mode for ctx to <mode>.

       SSL_CTX_get_session_cache_mode() returns the currently
       used cache mode.

NOTES    [Toc]    [Back]

       The OpenSSL library can store/retrieve SSL/TLS sessions
       for later reuse.  The sessions can be held in memory for
       each ctx, if more than one SSL_CTX object is being maintained,
 the sessions are unique for each SSL_CTX object.

       In order to reuse a session, a client must send the session's
 id to the server. It can only send exactly one id.
       The server then decides whether it agrees in reusing the
       session or starts the handshake for a new session.

       A server will lookup up the session in its internal session
 storage. If the session is not found in internal
       storage or internal storage is deactivated, the server
       will try the external storage if available.

       Since a client may try to reuse a session intended for use
       in a different context, the session id context must be set
       by the server (see SSL_CTX_set_session_id_context(3)).

       The following session cache modes and modifiers are available:


       SSL_SESS_CACHE_OFF
           No session caching for client or server takes place.

       SSL_SESS_CACHE_CLIENT
           Client sessions are added to the session cache. As
           there is no reliable way for the OpenSSL library to
           know whether a session should be reused or which session
 to choose (due to the abstract BIO layer the SSL
           engine does not have details about the connection),
           the application must select the session to be reused
           by using the SSL_set_session(3) function. This option
           is not activated by default.

       SSL_SESS_CACHE_SERVER
           Server sessions are added to the session cache. When a
           client proposes a session to be reused, the session is
           looked up in the internal session cache.  If the session
 is found, the server will try to reuse the
           session.  This is the default.

       SSL_SESS_CACHE_BOTH
           Enable both SSL_SESS_CACHE_CLIENT and
           SSL_SESS_CACHE_SERVER at the same time.

       SSL_SESS_CACHE_NO_AUTO_CLEAR
           Normally the session cache is checked for expired sessions
 every 255 connections using the
           SSL_CTX_flush_sessions(3) function. Since this may
           lead to a delay which cannot be controlled, the automatic
 flushing may be disabled and SSL_CTX_flush_sessions(3) can be called explicitly by the application.

       SSL_SESS_CACHE_NO_INTERNAL_LOOKUP
           By setting this flag sessions are cached in the internal
 storage but they are not looked up automatically.
           If an external session cache is enabled, sessions are
           looked up in the external cache. As automatic lookup
           only applies for SSL/TLS servers, the flag has no
           effect on clients.

       The default mode is SSL_SESS_CACHE_SERVER.

RETURN VALUES    [Toc]    [Back]

       SSL_CTX_set_session_cache_mode() returns the previously
       set cache mode.

       SSL_CTX_get_session_cache_mode() returns the currently set
       cache mode.

SEE ALSO    [Toc]    [Back]

       ssl(3), SSL_set_session(3), SSL_session_reused(3),
       SSL_CTX_sess_number(3), SSL_CTX_sess_set_cache_size(3),
       SSL_CTX_sess_set_get_cb(3), SSL_CTX_set_session_id_context(3), SSL_CTX_set_timeout(3), SSL_CTX_flush_sessions(3)



2002-06-10                    0.SSL_CTX_set_session_cache_mode(3)