Update build for OpenSSL-0.9.8j upgrade.
[dragonfly.git] / secure / lib / libssl / man / SSL_CTX_set_session_cache_mode.3
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132.\" ========================================================================
133.\"
134.IX Title "SSL_CTX_set_session_cache_mode 3"
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135.TH SSL_CTX_set_session_cache_mode 3 "2009-01-11" "0.9.8j" "OpenSSL"
136.\" For nroff, turn off justification. Always turn off hyphenation; it makes
137.\" way too many mistakes in technical documents.
138.if n .ad l
139.nh
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140.SH "NAME"
141SSL_CTX_set_session_cache_mode, SSL_CTX_get_session_cache_mode \- enable/disable session caching
142.SH "SYNOPSIS"
e056f0e0 143.IX Header "SYNOPSIS"
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144.Vb 1
145\& #include <openssl/ssl.h>
e257b235 146\&
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147\& long SSL_CTX_set_session_cache_mode(SSL_CTX ctx, long mode);
148\& long SSL_CTX_get_session_cache_mode(SSL_CTX ctx);
149.Ve
150.SH "DESCRIPTION"
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151.IX Header "DESCRIPTION"
152\&\fISSL_CTX_set_session_cache_mode()\fR enables/disables session caching
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153by setting the operational mode for \fBctx\fR to <mode>.
154.PP
e056f0e0 155\&\fISSL_CTX_get_session_cache_mode()\fR returns the currently used cache mode.
984263bc 156.SH "NOTES"
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157.IX Header "NOTES"
158The OpenSSL library can store/retrieve \s-1SSL/TLS\s0 sessions for later reuse.
984263bc 159The sessions can be held in memory for each \fBctx\fR, if more than one
e056f0e0 160\&\s-1SSL_CTX\s0 object is being maintained, the sessions are unique for each \s-1SSL_CTX\s0
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161object.
162.PP
163In order to reuse a session, a client must send the session's id to the
164server. It can only send exactly one id. The server then either
165agrees to reuse the session or it starts a full handshake (to create a new
166session).
167.PP
168A server will lookup up the session in its internal session storage. If the
169session is not found in internal storage or lookups for the internal storage
e056f0e0 170have been deactivated (\s-1SSL_SESS_CACHE_NO_INTERNAL_LOOKUP\s0), the server will try
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171the external storage if available.
172.PP
173Since a client may try to reuse a session intended for use in a different
174context, the session id context must be set by the server (see
e056f0e0 175\&\fISSL_CTX_set_session_id_context\fR\|(3)).
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176.PP
177The following session cache modes and modifiers are available:
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178.IP "\s-1SSL_SESS_CACHE_OFF\s0" 4
179.IX Item "SSL_SESS_CACHE_OFF"
984263bc 180No session caching for client or server takes place.
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181.IP "\s-1SSL_SESS_CACHE_CLIENT\s0" 4
182.IX Item "SSL_SESS_CACHE_CLIENT"
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183Client sessions are added to the session cache. As there is no reliable way
184for the OpenSSL library to know whether a session should be reused or which
185session to choose (due to the abstract \s-1BIO\s0 layer the \s-1SSL\s0 engine does not
186have details about the connection), the application must select the session
e056f0e0 187to be reused by using the \fISSL_set_session\fR\|(3)
984263bc 188function. This option is not activated by default.
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189.IP "\s-1SSL_SESS_CACHE_SERVER\s0" 4
190.IX Item "SSL_SESS_CACHE_SERVER"
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191Server sessions are added to the session cache. When a client proposes a
192session to be reused, the server looks for the corresponding session in (first)
193the internal session cache (unless \s-1SSL_SESS_CACHE_NO_INTERNAL_LOOKUP\s0 is set),
194then (second) in the external cache if available. If the session is found, the
195server will try to reuse the session. This is the default.
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196.IP "\s-1SSL_SESS_CACHE_BOTH\s0" 4
197.IX Item "SSL_SESS_CACHE_BOTH"
984263bc 198Enable both \s-1SSL_SESS_CACHE_CLIENT\s0 and \s-1SSL_SESS_CACHE_SERVER\s0 at the same time.
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199.IP "\s-1SSL_SESS_CACHE_NO_AUTO_CLEAR\s0" 4
200.IX Item "SSL_SESS_CACHE_NO_AUTO_CLEAR"
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201Normally the session cache is checked for expired sessions every
202255 connections using the
e056f0e0 203\&\fISSL_CTX_flush_sessions\fR\|(3) function. Since
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204this may lead to a delay which cannot be controlled, the automatic
205flushing may be disabled and
e056f0e0 206\&\fISSL_CTX_flush_sessions\fR\|(3) can be called
984263bc 207explicitly by the application.
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208.IP "\s-1SSL_SESS_CACHE_NO_INTERNAL_LOOKUP\s0" 4
209.IX Item "SSL_SESS_CACHE_NO_INTERNAL_LOOKUP"
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210By setting this flag, session-resume operations in an \s-1SSL/TLS\s0 server will not
211automatically look up sessions in the internal cache, even if sessions are
212automatically stored there. If external session caching callbacks are in use,
213this flag guarantees that all lookups are directed to the external cache.
214As automatic lookup only applies for \s-1SSL/TLS\s0 servers, the flag has no effect on
215clients.
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216.IP "\s-1SSL_SESS_CACHE_NO_INTERNAL_STORE\s0" 4
217.IX Item "SSL_SESS_CACHE_NO_INTERNAL_STORE"
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218Depending on the presence of \s-1SSL_SESS_CACHE_CLIENT\s0 and/or \s-1SSL_SESS_CACHE_SERVER\s0,
219sessions negotiated in an \s-1SSL/TLS\s0 handshake may be cached for possible reuse.
220Normally a new session is added to the internal cache as well as any external
221session caching (callback) that is configured for the \s-1SSL_CTX\s0. This flag will
222prevent sessions being stored in the internal cache (though the application can
e056f0e0 223add them manually using \fISSL_CTX_add_session\fR\|(3)). Note:
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224in any \s-1SSL/TLS\s0 servers where external caching is configured, any successful
225session lookups in the external cache (ie. for session-resume requests) would
226normally be copied into the local cache before processing continues \- this flag
227prevents these additions to the internal cache as well.
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228.IP "\s-1SSL_SESS_CACHE_NO_INTERNAL\s0" 4
229.IX Item "SSL_SESS_CACHE_NO_INTERNAL"
984263bc 230Enable both \s-1SSL_SESS_CACHE_NO_INTERNAL_LOOKUP\s0 and
e056f0e0 231\&\s-1SSL_SESS_CACHE_NO_INTERNAL_STORE\s0 at the same time.
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232.PP
233The default mode is \s-1SSL_SESS_CACHE_SERVER\s0.
234.SH "RETURN VALUES"
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235.IX Header "RETURN VALUES"
236\&\fISSL_CTX_set_session_cache_mode()\fR returns the previously set cache mode.
984263bc 237.PP
e056f0e0 238\&\fISSL_CTX_get_session_cache_mode()\fR returns the currently set cache mode.
984263bc 239.SH "SEE ALSO"
a7d27d5a 240.IX Header "SEE ALSO"
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241\&\fIssl\fR\|(3), \fISSL_set_session\fR\|(3),
242\&\fISSL_session_reused\fR\|(3),
243\&\fISSL_CTX_add_session\fR\|(3),
244\&\fISSL_CTX_sess_number\fR\|(3),
245\&\fISSL_CTX_sess_set_cache_size\fR\|(3),
246\&\fISSL_CTX_sess_set_get_cb\fR\|(3),
247\&\fISSL_CTX_set_session_id_context\fR\|(3),
248\&\fISSL_CTX_set_timeout\fR\|(3),
249\&\fISSL_CTX_flush_sessions\fR\|(3)
250.SH "HISTORY"
a7d27d5a 251.IX Header "HISTORY"
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252\&\s-1SSL_SESS_CACHE_NO_INTERNAL_STORE\s0 and \s-1SSL_SESS_CACHE_NO_INTERNAL\s0
253were introduced in OpenSSL 0.9.6h.