1SSL_CTX_set_session_cache_mode(3) OpenSSL SSL_CTX_set_session_cache_mode(3)
2
6 SSL_CTX_set_session_cache_mode, SSL_CTX_get_session_cache_mode -
7 enable/disable session caching
8
10 #include <openssl/ssl.h>
11 long SSL_CTX_set_session_cache_mode(SSL_CTX ctx, long mode);
13 long SSL_CTX_get_session_cache_mode(SSL_CTX ctx);
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16 SSL_CTX_set_session_cache_mode() enables/disables session caching by
17 setting the operational mode for ctx to <mode>.
18 SSL_CTX_get_session_cache_mode() returns the currently used cache mode.
20
22 The OpenSSL library can store/retrieve SSL/TLS sessions for later
23 reuse. The sessions can be held in memory for each ctx, if more than
24 one SSL_CTX object is being maintained, the sessions are unique for
25 each SSL_CTX object.
26 In order to reuse a session, a client must send the session's id to the
28 server. It can only send exactly one id. The server then either agrees
29 to reuse the session or it starts a full handshake (to create a new
30 session).
31 A server will look up the session in its internal session storage. If
33 the session is not found in internal storage or lookups for the
34 internal storage have been deactivated
35 (SSL_SESS_CACHE_NO_INTERNAL_LOOKUP), the server will try the external
36 storage if available.
37 Since a client may try to reuse a session intended for use in a
39 different context, the session id context must be set by the server
40 (see SSL_CTX_set_session_id_context(3)).
41 The following session cache modes and modifiers are available:
43 SSL_SESS_CACHE_OFF
45 No session caching for client or server takes place.
46 SSL_SESS_CACHE_CLIENT
48 Client sessions are added to the session cache. As there is no
49 reliable way for the OpenSSL library to know whether a session
50 should be reused or which session to choose (due to the abstract
51 BIO layer the SSL engine does not have details about the
52 connection), the application must select the session to be reused
53 by using the SSL_set_session(3) function. This option is not
54 activated by default.
55 SSL_SESS_CACHE_SERVER
57 Server sessions are added to the session cache. When a client
58 proposes a session to be reused, the server looks for the
59 corresponding session in (first) the internal session cache (unless
60 SSL_SESS_CACHE_NO_INTERNAL_LOOKUP is set), then (second) in the
61 external cache if available. If the session is found, the server
62 will try to reuse the session. This is the default.
63 SSL_SESS_CACHE_BOTH
65 Enable both SSL_SESS_CACHE_CLIENT and SSL_SESS_CACHE_SERVER at the
66 same time.
67 SSL_SESS_CACHE_NO_AUTO_CLEAR
69 Normally the session cache is checked for expired sessions every
70 255 connections using the SSL_CTX_flush_sessions(3) function. Since
71 this may lead to a delay which cannot be controlled, the automatic
72 flushing may be disabled and SSL_CTX_flush_sessions(3) can be
73 called explicitly by the application.
74 SSL_SESS_CACHE_NO_INTERNAL_LOOKUP
76 By setting this flag, session-resume operations in an SSL/TLS
77 server will not automatically look up sessions in the internal
78 cache, even if sessions are automatically stored there. If external
79 session caching callbacks are in use, this flag guarantees that all
80 lookups are directed to the external cache. As automatic lookup
81 only applies for SSL/TLS servers, the flag has no effect on
82 clients.
83 SSL_SESS_CACHE_NO_INTERNAL_STORE
85 Depending on the presence of SSL_SESS_CACHE_CLIENT and/or
86 SSL_SESS_CACHE_SERVER, sessions negotiated in an SSL/TLS handshake
87 may be cached for possible reuse. Normally a new session is added
88 to the internal cache as well as any external session caching
89 (callback) that is configured for the SSL_CTX. This flag will
90 prevent sessions being stored in the internal cache (though the
91 application can add them manually using SSL_CTX_add_session(3)).
92 Note: in any SSL/TLS servers where external caching is configured,
93 any successful session lookups in the external cache (ie. for
94 session-resume requests) would normally be copied into the local
95 cache before processing continues - this flag prevents these
96 additions to the internal cache as well.
97 SSL_SESS_CACHE_NO_INTERNAL
99 Enable both SSL_SESS_CACHE_NO_INTERNAL_LOOKUP and
100 SSL_SESS_CACHE_NO_INTERNAL_STORE at the same time.
101 The default mode is SSL_SESS_CACHE_SERVER.
103
105 SSL_CTX_set_session_cache_mode() returns the previously set cache mode.
106 SSL_CTX_get_session_cache_mode() returns the currently set cache mode.
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110 ssl(3), SSL_set_session(3), SSL_session_reused(3),
111 SSL_CTX_add_session(3), SSL_CTX_sess_number(3),
112 SSL_CTX_sess_set_cache_size(3), SSL_CTX_sess_set_get_cb(3),
113 SSL_CTX_set_session_id_context(3), SSL_CTX_set_timeout(3),
114 SSL_CTX_flush_sessions(3)
115
117 SSL_SESS_CACHE_NO_INTERNAL_STORE and SSL_SESS_CACHE_NO_INTERNAL were
118 introduced in OpenSSL 0.9.6h.
1191.0.2o 2020-08-01 SSL_CTX_set_session_cache_mode(3)