MirBSD manpage: SSL_CTX_get_session_cache_mode(3), SSL_CTX_set_session_cache_mode(3)



     SSL_CTX_get_session_cache_mode - enable/disable session


      #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);


     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.


     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 either agrees to reuse the session or it
     starts a full handshake (to create 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
     lookups for the internal storage have been deactivated
     (SSL_SESS_CACHE_NO_INTERNAL_LOOKUP), 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 avail-

         No session caching for client or server takes place.

         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 appli-
         cation must select the session to be reused by using the

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         SSL_set_session(3) function. This option is not
         activated by default.

         Server sessions are added to the session cache. When a
         client proposes a session to be reused, the server looks
         for the corresponding session in (first) the internal
         session cache (unless SSL_SESS_CACHE_NO_INTERNAL_LOOKUP
         is set), then (second) in the external cache if avail-
         able. If the session is found, the server will try to
         reuse the session.  This is the default.

         Enable both SSL_SESS_CACHE_CLIENT and
         SSL_SESS_CACHE_SERVER at the same time.

         Normally the session cache is checked for expired ses-
         sions 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.

         By setting this flag, session-resume operations in an
         SSL/TLS server will not automatically look up sessions
         in the internal cache, even if sessions are automati-
         cally stored there. If external session caching call-
         backs are in use, this flag guarantees that all lookups
         are directed to the external cache. As automatic lookup
         only applies for SSL/TLS servers, the flag has no effect
         on clients.

         Depending on the presence of SSL_SESS_CACHE_CLIENT
         and/or SSL_SESS_CACHE_SERVER, sessions negotiated in an
         SSL/TLS handshake may be cached for possible reuse. Nor-
         mally a new session is added to the internal cache as
         well as any external session caching (callback) that is
         configured for the SSL_CTX. This flag will prevent ses-
         sions being stored in the internal cache (though the
         application can add them manually using
         SSL_CTX_add_session(3)). Note: in any SSL/TLS servers
         where external caching is configured, any successful
         session lookups in the external cache (ie. for session-
         resume requests) would normally be copied into the local
         cache before processing continues - this flag prevents
         these additions to the internal cache as well.

         Enable both SSL_SESS_CACHE_NO_INTERNAL_LOOKUP and

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         SSL_SESS_CACHE_NO_INTERNAL_STORE at the same time.

     The default mode is SSL_SESS_CACHE_SERVER.


     SSL_CTX_set_session_cache_mode() returns the previously set
     cache mode.

     SSL_CTX_get_session_cache_mode() returns the currently set
     cache mode.


     ssl(3), SSL_set_session(3), SSL_session_reused(3),
     SSL_CTX_add_session(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_SESS_CACHE_NO_INTERNAL were introduced in OpenSSL

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