107 lines
3.6 KiB
Text
107 lines
3.6 KiB
Text
=pod
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=head1 NAME
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SSL_CTX_set_session_cache_mode, SSL_CTX_get_session_cache_mode - enable/disable session caching
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=head1 SYNOPSIS
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#include <openssl/ssl.h>
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long SSL_CTX_set_session_cache_mode(SSL_CTX ctx, long mode);
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long SSL_CTX_get_session_cache_mode(SSL_CTX ctx);
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=head1 DESCRIPTION
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SSL_CTX_set_session_cache_mode() enables/disables session caching
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by setting the operational mode for B<ctx> to <mode>.
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SSL_CTX_get_session_cache_mode() returns the currently used cache mode.
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=head1 NOTES
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The OpenSSL library can store/retrieve SSL/TLS sessions for later reuse.
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The sessions can be held in memory for each B<ctx>, if more than one
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SSL_CTX object is being maintained, the sessions are unique for each SSL_CTX
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object.
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In order to reuse a session, a client must send the session's id to the
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server. It can only send exactly one id. The server then decides whether it
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agrees in reusing the session or starts the handshake for a new session.
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A server will lookup up the session in its internal session storage. If
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the session is not found in internal storage or internal storage is
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deactivated, the server will try the external storage if available.
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Since a client may try to reuse a session intended for use in a different
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context, the session id context must be set by the server (see
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L<SSL_CTX_set_session_id_context(3)|SSL_CTX_set_session_id_context(3)>).
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The following session cache modes and modifiers are available:
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=over 4
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=item SSL_SESS_CACHE_OFF
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No session caching for client or server takes place.
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=item SSL_SESS_CACHE_CLIENT
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Client sessions are added to the session cache. As there is no reliable way
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for the OpenSSL library to know whether a session should be reused or which
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session to choose (due to the abstract BIO layer the SSL engine does not
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have details about the connection), the application must select the session
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to be reused by using the L<SSL_set_session(3)|SSL_set_session(3)>
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function. This option is not activated by default.
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=item SSL_SESS_CACHE_SERVER
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Server sessions are added to the session cache. When a client proposes a
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session to be reused, the session is looked up in the internal session cache.
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If the session is found, the server will try to reuse the session.
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This is the default.
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=item SSL_SESS_CACHE_BOTH
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Enable both SSL_SESS_CACHE_CLIENT and SSL_SESS_CACHE_SERVER at the same time.
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=item SSL_SESS_CACHE_NO_AUTO_CLEAR
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Normally the session cache is checked for expired sessions every
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255 connections using the
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L<SSL_CTX_flush_sessions(3)|SSL_CTX_flush_sessions(3)> function. Since
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this may lead to a delay which cannot be controlled, the automatic
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flushing may be disabled and
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L<SSL_CTX_flush_sessions(3)|SSL_CTX_flush_sessions(3)> can be called
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explicitly by the application.
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=item SSL_SESS_CACHE_NO_INTERNAL_LOOKUP
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By setting this flag sessions are cached in the internal storage but
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they are not looked up automatically. If an external session cache
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is enabled, sessions are looked up in the external cache. As automatic
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lookup only applies for SSL/TLS servers, the flag has no effect on
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clients.
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=back
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The default mode is SSL_SESS_CACHE_SERVER.
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=head1 RETURN VALUES
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SSL_CTX_set_session_cache_mode() returns the previously set cache mode.
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SSL_CTX_get_session_cache_mode() returns the currently set cache mode.
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=head1 SEE ALSO
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L<ssl(3)|ssl(3)>, L<SSL_set_session(3)|SSL_set_session(3)>,
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L<SSL_CTX_sess_number(3)|SSL_CTX_sess_number(3)>,
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L<SSL_CTX_sess_set_cache_size(3)|SSL_CTX_sess_set_cache_size(3)>,
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L<SSL_CTX_sess_set_get_cb(3)|SSL_CTX_sess_set_get_cb(3)>,
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L<SSL_CTX_set_session_id_context(3)|SSL_CTX_set_session_id_context(3)>,
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L<SSL_CTX_set_timeout.pod(3)|SSL_CTX_set_timeout.pod(3)>,
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L<SSL_CTX_flush_sessions(3)|SSL_CTX_flush_sessions(3)>
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=cut
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