.\" $OpenBSD: SSL_renegotiate.3,v 1.9 2019/06/12 09:36:30 schwarze Exp $ .\" OpenSSL SSL_key_update.pod 4fbfe86a Feb 16 17:04:40 2017 +0000 .\" .\" This file is a derived work. .\" Some parts are covered by the following Copyright and license: .\" .\" Copyright (c) 2016, 2017 Ingo Schwarze .\" .\" Permission to use, copy, modify, and distribute this software for any .\" purpose with or without fee is hereby granted, provided that the above .\" copyright notice and this permission notice appear in all copies. .\" .\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES .\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF .\" MERCHANTABILITY AND FITNESS. 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IN NO EVENT SHALL THE OpenSSL PROJECT OR .\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, .\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; .\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, .\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED .\" OF THE POSSIBILITY OF SUCH DAMAGE. .\" .Dd $Mdocdate: June 12 2019 $ .Dt SSL_RENEGOTIATE 3 .Os .Sh NAME .Nm SSL_renegotiate , .Nm SSL_renegotiate_abbreviated , .Nm SSL_renegotiate_pending .Nd initiate a new TLS handshake .Sh SYNOPSIS .In openssl/ssl.h .Ft int .Fo SSL_renegotiate .Fa "SSL *ssl" .Fc .Ft int .Fo SSL_renegotiate_abbreviated .Fa "SSL *ssl" .Fc .Ft int .Fo SSL_renegotiate_pending .Fa "SSL *ssl" .Fc .Sh DESCRIPTION When called from the client side, .Fn SSL_renegotiate schedules a completely new handshake over an existing TLS connection. The next time an I/O operation such as .Fn SSL_read or .Fn SSL_write takes place on the connection, a check is performed to confirm that it is a suitable time to start a renegotiation. If so, a new handshake is initiated immediately. An existing session associated with the connection is not resumed. .Pp This function is automatically called by .Xr SSL_read 3 and .Xr SSL_write 3 whenever the renegotiation byte count set by .Xr BIO_set_ssl_renegotiate_bytes 3 or the timeout set by .Xr BIO_set_ssl_renegotiate_timeout 3 are exceeded. .Pp When called from the client side, .Fn SSL_renegotiate_abbreviated is similar to .Fn SSL_renegotiate except that resuming the session associated with the current connection is attempted in the new handshake. .Pp When called from the server side, .Fn SSL_renegotiate and .Fn SSL_renegotiate_abbreviated behave identically. They both schedule a request for a new handshake to be sent to the client. The next time an I/O operation is performed, 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, it is handled transparently during any I/O function. .Pp If a LibreSSL client receives a renegotiation request from a server, it is also handled transparently during any I/O function. The client attempts to resume the current session in the new handshake. For historical reasons, DTLS clients do not attempt to resume the session in the new handshake. .Sh RETURN VALUES .Fn SSL_renegotiate and .Fn SSL_renegotiate_abbreviated return 1 on success or 0 on error. .Pp .Fn SSL_renegotiate_pending returns 1 if a renegotiation or renegotiation request has been scheduled but not yet acted on, or 0 otherwise. .Sh SEE ALSO .Xr ssl 3 , .Xr SSL_do_handshake 3 , .Xr SSL_num_renegotiations 3 , .Xr SSL_read 3 , .Xr SSL_write 3 .Sh HISTORY .Fn SSL_renegotiate first appeared in SSLeay 0.8.0 and has been available since .Ox 2.4 . .Pp .Fn SSL_renegotiate_pending first appeared in OpenSSL 0.9.7 and has been available since .Ox 3.2 . .Pp .Fn SSL_renegotiate_abbreviated first appeared in OpenSSL 1.0.1 and has been available since .Ox 5.3 .