/xlv3/openssl/0.9.7e-sgipl1/work/0.9.7e-sgipl1/openssl-
0.9.7e/doc/ssl
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SSL_CTX_set_session_cac29/Oct/20SSL_CTX_set_session_cache_mode(3)
NAME
SSL_CTX_set_session_cache_mode,
SSL_CTX_get_session_cache_mode - enable/disable session
caching
SYNOPSIS
#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
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
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
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
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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 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
available. 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, session-resume operations in an
SSL/TLS server will not automatically look up sessions
in the internal cache, even if sessions are
automatically stored there. If external session caching
callbacks 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.
SSL_SESS_CACHE_NO_INTERNAL_STORE
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.
Normally 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
sessions 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.
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SSL_SESS_CACHE_NO_INTERNAL
Enable both SSL_SESS_CACHE_NO_INTERNAL_LOOKUP and
SSL_SESS_CACHE_NO_INTERNAL_STORE at the same time.
The default mode is SSL_SESS_CACHE_SERVER.
RETURN VALUES
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
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_CTX_flush_sessions(3)
HISTORY
SSL_SESS_CACHE_NO_INTERNAL_STORE and
SSL_SESS_CACHE_NO_INTERNAL were introduced in OpenSSL
0.9.6h.
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