NAME

       SSL_key_update, SSL_get_key_update_type, SSL_renegotiate, SSL_renegotiate_abbreviated,
       SSL_renegotiate_pending - initiate and obtain information about updating connection keys

SYNOPSIS

        #include <openssl/ssl.h>

        int SSL_key_update(SSL *s, int updatetype);
        int SSL_get_key_update_type(const SSL *s);

        int SSL_renegotiate(SSL *s);
        int SSL_renegotiate_abbreviated(SSL *s);
        int SSL_renegotiate_pending(const SSL *s);

DESCRIPTION

       SSL_key_update() schedules an update of the keys for the current TLS connection.  If the
       updatetype parameter is set to SSL_KEY_UPDATE_NOT_REQUESTED then the sending keys for this
       connection will be updated and the peer will be informed of the change. If the updatetype
       parameter is set to SSL_KEY_UPDATE_REQUESTED then the sending keys for this connection
       will be updated and the peer will be informed of the change along with a request for the
       peer to additionally update its sending keys. It is an error if updatetype is set to
       SSL_KEY_UPDATE_NONE.

       SSL_key_update() must only be called after the initial handshake has been completed and
       TLSv1.3 has been negotiated, at the same time, the application needs to ensure that the
       writing of data has been completed. The key update will not take place until the next time
       an IO operation such as SSL_read_ex() or SSL_write_ex() takes place on the connection.
       Alternatively SSL_do_handshake() can be called to force the update to take place
       immediately.

       SSL_get_key_update_type() can be used to determine whether a key update operation has been
       scheduled but not yet performed. The type of the pending key update operation will be
       returned if there is one, or SSL_KEY_UPDATE_NONE otherwise.

       SSL_renegotiate() and SSL_renegotiate_abbreviated() should only be called for connections
       that have negotiated TLSv1.2 or less. Calling them on any other connection will result in
       an error.

       When called from the client side, SSL_renegotiate() schedules a completely new handshake
       over an existing SSL/TLS connection. The next time an IO operation such as SSL_read_ex()
       or SSL_write_ex() takes place on the connection a check will be performed to confirm that
       it is a suitable time to start a renegotiation. If so, then it will be initiated
       immediately. OpenSSL will not attempt to resume any session associated with the connection
       in the new handshake.

       When called from the client side, SSL_renegotiate_abbreviated() works in the same was as
       SSL_renegotiate() except that OpenSSL will attempt to resume the session associated with
       the current connection in the new handshake.

       When called from the server side, SSL_renegotiate() and SSL_renegotiate_abbreviated()
       behave identically. They both schedule a request for a new handshake to be sent to the
       client. The next time an IO operation is performed then the same checks as on the client
       side are performed and then, if appropriate, the request is sent. The client may or may
       not respond with a new handshake and it may or may not attempt to resume an existing
       session. If a new handshake is started then this will be handled transparently by calling
       any OpenSSL IO function.

       If an OpenSSL client receives a renegotiation request from a server then again this will
       be handled transparently through calling any OpenSSL IO function. For a TLS connection the
       client will attempt to resume the current session in the new handshake. For historical
       reasons, DTLS clients will not attempt to resume the session in the new handshake.

       The SSL_renegotiate_pending() function returns 1 if a renegotiation or renegotiation
       request has been scheduled but not yet acted on, or 0 otherwise.

RETURN VALUES

       SSL_key_update(), SSL_renegotiate() and SSL_renegotiate_abbreviated() return 1 on success
       or 0 on error.

       SSL_get_key_update_type() returns the update type of the pending key update operation or
       SSL_KEY_UPDATE_NONE if there is none.

       SSL_renegotiate_pending() returns 1 if a renegotiation or renegotiation request has been
       scheduled but not yet acted on, or 0 otherwise.

SEE ALSO

       ssl(7), SSL_read_ex(3), SSL_write_ex(3), SSL_do_handshake(3)

HISTORY

       The SSL_key_update() and SSL_get_key_update_type() functions were added in OpenSSL 1.1.1.

COPYRIGHT

       Copyright 2017-2021 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the Apache License 2.0 (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 <https://www.openssl.org/source/license.html>.