Updated: 2021/Apr/14

SSL_CTX_set_session_id_context(3)   OpenSSL  SSL_CTX_set_session_id_context(3)

       SSL_CTX_set_session_id_context, SSL_set_session_id_context - set
       context within which session can be reused (server side only)

       libcrypto, -lcrypto

        #include <openssl/ssl.h>

        int SSL_CTX_set_session_id_context(SSL_CTX *ctx, const unsigned char *sid_ctx,
                                           unsigned int sid_ctx_len);
        int SSL_set_session_id_context(SSL *ssl, const unsigned char *sid_ctx,
                                       unsigned int sid_ctx_len);

       SSL_CTX_set_session_id_context() sets the context sid_ctx of length
       sid_ctx_len within which a session can be reused for the ctx object.

       SSL_set_session_id_context() sets the context sid_ctx of length
       sid_ctx_len within which a session can be reused for the ssl object.

       Sessions are generated within a certain context. When
       exporting/importing sessions with i2d_SSL_SESSION/d2i_SSL_SESSION it
       would be possible, to re-import a session generated from another
       context (e.g. another application), which might lead to malfunctions.
       Therefore, each application must set its own session id context sid_ctx
       which is used to distinguish the contexts and is stored in exported
       sessions. The sid_ctx can be any kind of binary data with a given
       length, it is therefore possible to use e.g. the name of the
       application and/or the hostname and/or service name ...

       The session id context becomes part of the session. The session id
       context is set by the SSL/TLS server. The
       SSL_CTX_set_session_id_context() and SSL_set_session_id_context()
       functions are therefore only useful on the server side.

       OpenSSL clients will check the session id context returned by the
       server when reusing a session.

       The maximum length of the sid_ctx is limited to SSL_MAX_SID_CTX_LENGTH.

       If the session id context is not set on an SSL/TLS server and client
       certificates are used, stored sessions will not be reused but a fatal
       error will be flagged and the handshake will fail.

       If a server returns a different session id context to an OpenSSL client
       when reusing a session, an error will be flagged and the handshake will
       fail. OpenSSL servers will always return the correct session id
       context, as an OpenSSL server checks the session id context itself
       before reusing a session as described above.

       SSL_CTX_set_session_id_context() and SSL_set_session_id_context()
       return the following values:

       0   The length sid_ctx_len of the session id context sid_ctx exceeded
           the maximum allowed length of SSL_MAX_SID_CTX_LENGTH. The error is
           logged to the error stack.

       1   The operation succeeded.


       Copyright 2001-2020 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the OpenSSL license (the "License").  You may not use
       this file except in compliance with the License.  You can obtain a copy
       in the file LICENSE in the source distribution or at

1.1.1i                            2020-12-10 SSL_CTX_set_session_id_context(3)