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[dragonfly.git] / secure / lib / libssl / man / SSL_CTX_set_session_cache_mode.3
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129.\" ========================================================================
130.\"
131.IX Title "SSL_CTX_set_session_cache_mode 3"
132.TH SSL_CTX_set_session_cache_mode 3 "2004-12-22" "0.9.7e" "OpenSSL"
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133.SH "NAME"
134SSL_CTX_set_session_cache_mode, SSL_CTX_get_session_cache_mode \- enable/disable session caching
135.SH "SYNOPSIS"
e056f0e0 136.IX Header "SYNOPSIS"
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137.Vb 1
138\& #include <openssl/ssl.h>
139.Ve
e056f0e0 140.PP
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141.Vb 2
142\& long SSL_CTX_set_session_cache_mode(SSL_CTX ctx, long mode);
143\& long SSL_CTX_get_session_cache_mode(SSL_CTX ctx);
144.Ve
145.SH "DESCRIPTION"
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146.IX Header "DESCRIPTION"
147\&\fISSL_CTX_set_session_cache_mode()\fR enables/disables session caching
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148by setting the operational mode for \fBctx\fR to <mode>.
149.PP
e056f0e0 150\&\fISSL_CTX_get_session_cache_mode()\fR returns the currently used cache mode.
984263bc 151.SH "NOTES"
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152.IX Header "NOTES"
153The OpenSSL library can store/retrieve \s-1SSL/TLS\s0 sessions for later reuse.
984263bc 154The sessions can be held in memory for each \fBctx\fR, if more than one
e056f0e0 155\&\s-1SSL_CTX\s0 object is being maintained, the sessions are unique for each \s-1SSL_CTX\s0
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156object.
157.PP
158In order to reuse a session, a client must send the session's id to the
159server. It can only send exactly one id. The server then either
160agrees to reuse the session or it starts a full handshake (to create a new
161session).
162.PP
163A server will lookup up the session in its internal session storage. If the
164session is not found in internal storage or lookups for the internal storage
e056f0e0 165have been deactivated (\s-1SSL_SESS_CACHE_NO_INTERNAL_LOOKUP\s0), the server will try
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166the external storage if available.
167.PP
168Since a client may try to reuse a session intended for use in a different
169context, the session id context must be set by the server (see
e056f0e0 170\&\fISSL_CTX_set_session_id_context\fR\|(3)).
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171.PP
172The following session cache modes and modifiers are available:
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173.IP "\s-1SSL_SESS_CACHE_OFF\s0" 4
174.IX Item "SSL_SESS_CACHE_OFF"
984263bc 175No session caching for client or server takes place.
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176.IP "\s-1SSL_SESS_CACHE_CLIENT\s0" 4
177.IX Item "SSL_SESS_CACHE_CLIENT"
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178Client sessions are added to the session cache. As there is no reliable way
179for the OpenSSL library to know whether a session should be reused or which
180session to choose (due to the abstract \s-1BIO\s0 layer the \s-1SSL\s0 engine does not
181have details about the connection), the application must select the session
e056f0e0 182to be reused by using the \fISSL_set_session\fR\|(3)
984263bc 183function. This option is not activated by default.
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184.IP "\s-1SSL_SESS_CACHE_SERVER\s0" 4
185.IX Item "SSL_SESS_CACHE_SERVER"
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186Server sessions are added to the session cache. When a client proposes a
187session to be reused, the server looks for the corresponding session in (first)
188the internal session cache (unless \s-1SSL_SESS_CACHE_NO_INTERNAL_LOOKUP\s0 is set),
189then (second) in the external cache if available. If the session is found, the
190server will try to reuse the session. This is the default.
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191.IP "\s-1SSL_SESS_CACHE_BOTH\s0" 4
192.IX Item "SSL_SESS_CACHE_BOTH"
984263bc 193Enable both \s-1SSL_SESS_CACHE_CLIENT\s0 and \s-1SSL_SESS_CACHE_SERVER\s0 at the same time.
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194.IP "\s-1SSL_SESS_CACHE_NO_AUTO_CLEAR\s0" 4
195.IX Item "SSL_SESS_CACHE_NO_AUTO_CLEAR"
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196Normally the session cache is checked for expired sessions every
197255 connections using the
e056f0e0 198\&\fISSL_CTX_flush_sessions\fR\|(3) function. Since
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199this may lead to a delay which cannot be controlled, the automatic
200flushing may be disabled and
e056f0e0 201\&\fISSL_CTX_flush_sessions\fR\|(3) can be called
984263bc 202explicitly by the application.
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203.IP "\s-1SSL_SESS_CACHE_NO_INTERNAL_LOOKUP\s0" 4
204.IX Item "SSL_SESS_CACHE_NO_INTERNAL_LOOKUP"
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205By setting this flag, session-resume operations in an \s-1SSL/TLS\s0 server will not
206automatically look up sessions in the internal cache, even if sessions are
207automatically stored there. If external session caching callbacks are in use,
208this flag guarantees that all lookups are directed to the external cache.
209As automatic lookup only applies for \s-1SSL/TLS\s0 servers, the flag has no effect on
210clients.
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211.IP "\s-1SSL_SESS_CACHE_NO_INTERNAL_STORE\s0" 4
212.IX Item "SSL_SESS_CACHE_NO_INTERNAL_STORE"
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213Depending on the presence of \s-1SSL_SESS_CACHE_CLIENT\s0 and/or \s-1SSL_SESS_CACHE_SERVER\s0,
214sessions negotiated in an \s-1SSL/TLS\s0 handshake may be cached for possible reuse.
215Normally a new session is added to the internal cache as well as any external
216session caching (callback) that is configured for the \s-1SSL_CTX\s0. This flag will
217prevent sessions being stored in the internal cache (though the application can
e056f0e0 218add them manually using \fISSL_CTX_add_session\fR\|(3)). Note:
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219in any \s-1SSL/TLS\s0 servers where external caching is configured, any successful
220session lookups in the external cache (ie. for session-resume requests) would
221normally be copied into the local cache before processing continues \- this flag
222prevents these additions to the internal cache as well.
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223.IP "\s-1SSL_SESS_CACHE_NO_INTERNAL\s0" 4
224.IX Item "SSL_SESS_CACHE_NO_INTERNAL"
984263bc 225Enable both \s-1SSL_SESS_CACHE_NO_INTERNAL_LOOKUP\s0 and
e056f0e0 226\&\s-1SSL_SESS_CACHE_NO_INTERNAL_STORE\s0 at the same time.
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227.PP
228The default mode is \s-1SSL_SESS_CACHE_SERVER\s0.
229.SH "RETURN VALUES"
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230.IX Header "RETURN VALUES"
231\&\fISSL_CTX_set_session_cache_mode()\fR returns the previously set cache mode.
984263bc 232.PP
e056f0e0 233\&\fISSL_CTX_get_session_cache_mode()\fR returns the currently set cache mode.
984263bc 234.SH "SEE ALSO"
a7d27d5a 235.IX Header "SEE ALSO"
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236\&\fIssl\fR\|(3), \fISSL_set_session\fR\|(3),
237\&\fISSL_session_reused\fR\|(3),
238\&\fISSL_CTX_add_session\fR\|(3),
239\&\fISSL_CTX_sess_number\fR\|(3),
240\&\fISSL_CTX_sess_set_cache_size\fR\|(3),
241\&\fISSL_CTX_sess_set_get_cb\fR\|(3),
242\&\fISSL_CTX_set_session_id_context\fR\|(3),
243\&\fISSL_CTX_set_timeout\fR\|(3),
244\&\fISSL_CTX_flush_sessions\fR\|(3)
245.SH "HISTORY"
a7d27d5a 246.IX Header "HISTORY"
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247\&\s-1SSL_SESS_CACHE_NO_INTERNAL_STORE\s0 and \s-1SSL_SESS_CACHE_NO_INTERNAL\s0
248were introduced in OpenSSL 0.9.6h.