Update files for OpenSSL-1.0.0f import.
[dragonfly.git] / secure / lib / libssl / man / SSL_CTX_set_session_cache_mode.3
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124.\" ========================================================================
125.\"
126.IX Title "SSL_CTX_set_session_cache_mode 3"
e3261593 127.TH SSL_CTX_set_session_cache_mode 3 "2012-01-04" "1.0.0f" "OpenSSL"
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128.\" For nroff, turn off justification. Always turn off hyphenation; it makes
129.\" way too many mistakes in technical documents.
130.if n .ad l
131.nh
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132.SH "NAME"
133SSL_CTX_set_session_cache_mode, SSL_CTX_get_session_cache_mode \- enable/disable session caching
134.SH "SYNOPSIS"
e056f0e0 135.IX Header "SYNOPSIS"
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136.Vb 1
137\& #include <openssl/ssl.h>
e257b235 138\&
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139\& long SSL_CTX_set_session_cache_mode(SSL_CTX ctx, long mode);
140\& long SSL_CTX_get_session_cache_mode(SSL_CTX ctx);
141.Ve
142.SH "DESCRIPTION"
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143.IX Header "DESCRIPTION"
144\&\fISSL_CTX_set_session_cache_mode()\fR enables/disables session caching
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145by setting the operational mode for \fBctx\fR to <mode>.
146.PP
e056f0e0 147\&\fISSL_CTX_get_session_cache_mode()\fR returns the currently used cache mode.
984263bc 148.SH "NOTES"
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149.IX Header "NOTES"
150The OpenSSL library can store/retrieve \s-1SSL/TLS\s0 sessions for later reuse.
984263bc 151The sessions can be held in memory for each \fBctx\fR, if more than one
e056f0e0 152\&\s-1SSL_CTX\s0 object is being maintained, the sessions are unique for each \s-1SSL_CTX\s0
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153object.
154.PP
155In order to reuse a session, a client must send the session's id to the
156server. It can only send exactly one id. The server then either
157agrees to reuse the session or it starts a full handshake (to create a new
158session).
159.PP
160A server will lookup up the session in its internal session storage. If the
161session is not found in internal storage or lookups for the internal storage
e056f0e0 162have been deactivated (\s-1SSL_SESS_CACHE_NO_INTERNAL_LOOKUP\s0), the server will try
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163the external storage if available.
164.PP
165Since a client may try to reuse a session intended for use in a different
166context, the session id context must be set by the server (see
e056f0e0 167\&\fISSL_CTX_set_session_id_context\fR\|(3)).
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168.PP
169The following session cache modes and modifiers are available:
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170.IP "\s-1SSL_SESS_CACHE_OFF\s0" 4
171.IX Item "SSL_SESS_CACHE_OFF"
984263bc 172No session caching for client or server takes place.
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173.IP "\s-1SSL_SESS_CACHE_CLIENT\s0" 4
174.IX Item "SSL_SESS_CACHE_CLIENT"
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175Client sessions are added to the session cache. As there is no reliable way
176for the OpenSSL library to know whether a session should be reused or which
177session to choose (due to the abstract \s-1BIO\s0 layer the \s-1SSL\s0 engine does not
178have details about the connection), the application must select the session
e056f0e0 179to be reused by using the \fISSL_set_session\fR\|(3)
984263bc 180function. This option is not activated by default.
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181.IP "\s-1SSL_SESS_CACHE_SERVER\s0" 4
182.IX Item "SSL_SESS_CACHE_SERVER"
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183Server sessions are added to the session cache. When a client proposes a
184session to be reused, the server looks for the corresponding session in (first)
185the internal session cache (unless \s-1SSL_SESS_CACHE_NO_INTERNAL_LOOKUP\s0 is set),
186then (second) in the external cache if available. If the session is found, the
187server will try to reuse the session. This is the default.
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188.IP "\s-1SSL_SESS_CACHE_BOTH\s0" 4
189.IX Item "SSL_SESS_CACHE_BOTH"
984263bc 190Enable both \s-1SSL_SESS_CACHE_CLIENT\s0 and \s-1SSL_SESS_CACHE_SERVER\s0 at the same time.
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191.IP "\s-1SSL_SESS_CACHE_NO_AUTO_CLEAR\s0" 4
192.IX Item "SSL_SESS_CACHE_NO_AUTO_CLEAR"
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193Normally the session cache is checked for expired sessions every
194255 connections using the
e056f0e0 195\&\fISSL_CTX_flush_sessions\fR\|(3) function. Since
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196this may lead to a delay which cannot be controlled, the automatic
197flushing may be disabled and
e056f0e0 198\&\fISSL_CTX_flush_sessions\fR\|(3) can be called
984263bc 199explicitly by the application.
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200.IP "\s-1SSL_SESS_CACHE_NO_INTERNAL_LOOKUP\s0" 4
201.IX Item "SSL_SESS_CACHE_NO_INTERNAL_LOOKUP"
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202By setting this flag, session-resume operations in an \s-1SSL/TLS\s0 server will not
203automatically look up sessions in the internal cache, even if sessions are
204automatically stored there. If external session caching callbacks are in use,
205this flag guarantees that all lookups are directed to the external cache.
206As automatic lookup only applies for \s-1SSL/TLS\s0 servers, the flag has no effect on
207clients.
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208.IP "\s-1SSL_SESS_CACHE_NO_INTERNAL_STORE\s0" 4
209.IX Item "SSL_SESS_CACHE_NO_INTERNAL_STORE"
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210Depending on the presence of \s-1SSL_SESS_CACHE_CLIENT\s0 and/or \s-1SSL_SESS_CACHE_SERVER\s0,
211sessions negotiated in an \s-1SSL/TLS\s0 handshake may be cached for possible reuse.
212Normally a new session is added to the internal cache as well as any external
213session caching (callback) that is configured for the \s-1SSL_CTX\s0. This flag will
214prevent sessions being stored in the internal cache (though the application can
e056f0e0 215add them manually using \fISSL_CTX_add_session\fR\|(3)). Note:
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216in any \s-1SSL/TLS\s0 servers where external caching is configured, any successful
217session lookups in the external cache (ie. for session-resume requests) would
218normally be copied into the local cache before processing continues \- this flag
219prevents these additions to the internal cache as well.
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220.IP "\s-1SSL_SESS_CACHE_NO_INTERNAL\s0" 4
221.IX Item "SSL_SESS_CACHE_NO_INTERNAL"
984263bc 222Enable both \s-1SSL_SESS_CACHE_NO_INTERNAL_LOOKUP\s0 and
e056f0e0 223\&\s-1SSL_SESS_CACHE_NO_INTERNAL_STORE\s0 at the same time.
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224.PP
225The default mode is \s-1SSL_SESS_CACHE_SERVER\s0.
226.SH "RETURN VALUES"
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227.IX Header "RETURN VALUES"
228\&\fISSL_CTX_set_session_cache_mode()\fR returns the previously set cache mode.
984263bc 229.PP
e056f0e0 230\&\fISSL_CTX_get_session_cache_mode()\fR returns the currently set cache mode.
984263bc 231.SH "SEE ALSO"
a7d27d5a 232.IX Header "SEE ALSO"
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233\&\fIssl\fR\|(3), \fISSL_set_session\fR\|(3),
234\&\fISSL_session_reused\fR\|(3),
235\&\fISSL_CTX_add_session\fR\|(3),
236\&\fISSL_CTX_sess_number\fR\|(3),
237\&\fISSL_CTX_sess_set_cache_size\fR\|(3),
238\&\fISSL_CTX_sess_set_get_cb\fR\|(3),
239\&\fISSL_CTX_set_session_id_context\fR\|(3),
240\&\fISSL_CTX_set_timeout\fR\|(3),
241\&\fISSL_CTX_flush_sessions\fR\|(3)
242.SH "HISTORY"
a7d27d5a 243.IX Header "HISTORY"
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244\&\s-1SSL_SESS_CACHE_NO_INTERNAL_STORE\s0 and \s-1SSL_SESS_CACHE_NO_INTERNAL\s0
245were introduced in OpenSSL 0.9.6h.