243 lines
9.8 KiB
Groff
Executable File
243 lines
9.8 KiB
Groff
Executable File
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.\" ========================================================================
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.\"
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.IX Title "SSL_CTX_SESS_SET_GET_CB 3"
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.TH SSL_CTX_SESS_SET_GET_CB 3 "2020-03-02" "3.0.0-dev" "OpenSSL"
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.\" way too many mistakes in technical documents.
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.if n .ad l
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.nh
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.SH "NAME"
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SSL_CTX_sess_set_new_cb, SSL_CTX_sess_set_remove_cb, SSL_CTX_sess_set_get_cb, SSL_CTX_sess_get_new_cb, SSL_CTX_sess_get_remove_cb, SSL_CTX_sess_get_get_cb \- provide callback functions for server side external session caching
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 1
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\& #include <openssl/ssl.h>
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\&
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\& void SSL_CTX_sess_set_new_cb(SSL_CTX *ctx,
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\& int (*new_session_cb)(SSL *, SSL_SESSION *));
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\& void SSL_CTX_sess_set_remove_cb(SSL_CTX *ctx,
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\& void (*remove_session_cb)(SSL_CTX *ctx,
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\& SSL_SESSION *));
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\& void SSL_CTX_sess_set_get_cb(SSL_CTX *ctx,
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\& SSL_SESSION (*get_session_cb)(SSL *,
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\& const unsigned char *,
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\& int, int *));
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\&
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\& int (*SSL_CTX_sess_get_new_cb(SSL_CTX *ctx))(struct ssl_st *ssl,
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\& SSL_SESSION *sess);
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\& void (*SSL_CTX_sess_get_remove_cb(SSL_CTX *ctx))(struct ssl_ctx_st *ctx,
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\& SSL_SESSION *sess);
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\& SSL_SESSION *(*SSL_CTX_sess_get_get_cb(SSL_CTX *ctx))(struct ssl_st *ssl,
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\& const unsigned char *data,
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\& int len, int *copy);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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\&\fISSL_CTX_sess_set_new_cb()\fR sets the callback function, which is automatically
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called whenever a new session was negotiated.
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.PP
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\&\fISSL_CTX_sess_set_remove_cb()\fR sets the callback function, which is
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automatically called whenever a session is removed by the \s-1SSL\s0 engine,
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because it is considered faulty or the session has become obsolete because
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of exceeding the timeout value.
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.PP
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\&\fISSL_CTX_sess_set_get_cb()\fR sets the callback function which is called,
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whenever a \s-1SSL/TLS\s0 client proposed to resume a session but the session
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could not be found in the internal session cache (see
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\&\fISSL_CTX_set_session_cache_mode\fR\|(3)).
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(\s-1SSL/TLS\s0 server only.)
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.PP
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\&\fISSL_CTX_sess_get_new_cb()\fR, \fISSL_CTX_sess_get_remove_cb()\fR, and
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\&\fISSL_CTX_sess_get_get_cb()\fR retrieve the function pointers set by the
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corresponding set callback functions. If a callback function has not been
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set, the \s-1NULL\s0 pointer is returned.
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.SH "NOTES"
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.IX Header "NOTES"
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In order to allow external session caching, synchronization with the internal
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session cache is realized via callback functions. Inside these callback
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functions, session can be saved to disk or put into a database using the
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\&\fId2i_SSL_SESSION\fR\|(3) interface.
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.PP
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The \fInew_session_cb()\fR is called whenever a new session has been negotiated and
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session caching is enabled (see \fISSL_CTX_set_session_cache_mode\fR\|(3)). The
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\&\fInew_session_cb()\fR is passed the \fBssl\fR connection and the ssl session \fBsess\fR.
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Since sessions are reference-counted objects, the reference count on the
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session is incremented before the callback, on behalf of the application. If
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the callback returns \fB0\fR, the session will be immediately removed from the
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internal cache and the reference count released. If the callback returns \fB1\fR,
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the application retains the reference (for an entry in the
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application-maintained \*(L"external session cache\*(R"), and is responsible for
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calling \fISSL_SESSION_free()\fR when the session reference is no longer in use.
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.PP
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Note that in TLSv1.3, sessions are established after the main
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handshake has completed. The server decides when to send the client the session
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information and this may occur some time after the end of the handshake (or not
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at all). This means that applications should expect the \fInew_session_cb()\fR
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function to be invoked during the handshake (for <= TLSv1.2) or after the
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handshake (for TLSv1.3). It is also possible in TLSv1.3 for multiple sessions to
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be established with a single connection. In these case the \fInew_session_cb()\fR
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function will be invoked multiple times.
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.PP
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In TLSv1.3 it is recommended that each \s-1SSL_SESSION\s0 object is only used for
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resumption once. One way of enforcing that is for applications to call
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\&\fISSL_CTX_remove_session\fR\|(3) after a session has been used.
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.PP
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The \fIremove_session_cb()\fR is called, whenever the \s-1SSL\s0 engine removes a session
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from the internal cache. This happens when the session is removed because
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it is expired or when a connection was not shutdown cleanly. It also happens
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for all sessions in the internal session cache when
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\&\fISSL_CTX_free\fR\|(3) is called. The \fIremove_session_cb()\fR is passed
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the \fBctx\fR and the ssl session \fBsess\fR. It does not provide any feedback.
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.PP
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The \fIget_session_cb()\fR is only called on \s-1SSL/TLS\s0 servers with the session id
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proposed by the client. The \fIget_session_cb()\fR is always called, also when
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session caching was disabled. The \fIget_session_cb()\fR is passed the
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\&\fBssl\fR connection, the session id of length \fBlength\fR at the memory location
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\&\fBdata\fR. With the parameter \fBcopy\fR the callback can require the
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\&\s-1SSL\s0 engine to increment the reference count of the \s-1SSL_SESSION\s0 object,
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Normally the reference count is not incremented and therefore the
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session must not be explicitly freed with
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\&\fISSL_SESSION_free\fR\|(3).
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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\&\fISSL_CTX_sess_get_new_cb()\fR, \fISSL_CTX_sess_get_remove_cb()\fR and \fISSL_CTX_sess_get_get_cb()\fR
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return different callback function pointers respectively.
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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\&\fIssl\fR\|(7), \fId2i_SSL_SESSION\fR\|(3),
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\&\fISSL_CTX_set_session_cache_mode\fR\|(3),
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\&\fISSL_CTX_flush_sessions\fR\|(3),
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\&\fISSL_SESSION_free\fR\|(3),
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\&\fISSL_CTX_free\fR\|(3)
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.SH "COPYRIGHT"
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.IX Header "COPYRIGHT"
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Copyright 2001\-2018 The OpenSSL Project Authors. All Rights Reserved.
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.PP
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Licensed under the Apache License 2.0 (the \*(L"License\*(R"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file \s-1LICENSE\s0 in the source distribution or at
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<https://www.openssl.org/source/license.html>.
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