1.\" $OpenBSD: SSL_do_handshake.3,v 1.6 2018/03/27 17:35:50 schwarze Exp $ 2.\" OpenSSL b97fdb57 Nov 11 09:33:09 2016 +0100 3.\" 4.\" This file was written by Martin Sjoegren <martin@strakt.com>. 5.\" Copyright (c) 2002 The OpenSSL Project. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in 16.\" the documentation and/or other materials provided with the 17.\" distribution. 18.\" 19.\" 3. All advertising materials mentioning features or use of this 20.\" software must display the following acknowledgment: 21.\" "This product includes software developed by the OpenSSL Project 22.\" for use in the OpenSSL Toolkit. (http://www.openssl.org/)" 23.\" 24.\" 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to 25.\" endorse or promote products derived from this software without 26.\" prior written permission. For written permission, please contact 27.\" openssl-core@openssl.org. 28.\" 29.\" 5. Products derived from this software may not be called "OpenSSL" 30.\" nor may "OpenSSL" appear in their names without prior written 31.\" permission of the OpenSSL Project. 32.\" 33.\" 6. Redistributions of any form whatsoever must retain the following 34.\" acknowledgment: 35.\" "This product includes software developed by the OpenSSL Project 36.\" for use in the OpenSSL Toolkit (http://www.openssl.org/)" 37.\" 38.\" THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY 39.\" EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 40.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 41.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR 42.\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 43.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 44.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 45.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 46.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 47.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 48.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED 49.\" OF THE POSSIBILITY OF SUCH DAMAGE. 50.\" 51.Dd $Mdocdate: March 27 2018 $ 52.Dt SSL_DO_HANDSHAKE 3 53.Os 54.Sh NAME 55.Nm SSL_do_handshake 56.Nd perform a TLS/SSL handshake 57.Sh SYNOPSIS 58.In openssl/ssl.h 59.Ft int 60.Fn SSL_do_handshake "SSL *ssl" 61.Sh DESCRIPTION 62.Fn SSL_do_handshake 63will wait for a SSL/TLS handshake to take place. 64If the connection is in client mode, the handshake will be started. 65The handshake routines may have to be explicitly set in advance using either 66.Xr SSL_set_connect_state 3 67or 68.Xr SSL_set_accept_state 3 . 69.Pp 70The behaviour of 71.Fn SSL_do_handshake 72depends on the underlying 73.Vt BIO . 74.Pp 75If the underlying 76.Vt BIO 77is 78.Em blocking , 79.Fn SSL_do_handshake 80will only return once the handshake has been finished or an error occurred. 81.Pp 82If the underlying 83.Vt BIO 84is 85.Em non-blocking , 86.Fn SSL_do_handshake 87will also return when the underlying 88.Vt BIO 89could not satisfy the needs of 90.Fn SSL_do_handshake 91to continue the handshake. 92In this case a call to 93.Xr SSL_get_error 3 94with the return value of 95.Fn SSL_do_handshake 96will yield 97.Dv SSL_ERROR_WANT_READ 98or 99.Dv SSL_ERROR_WANT_WRITE . 100The calling process then must repeat the call after taking appropriate action 101to satisfy the needs of 102.Fn SSL_do_handshake . 103The action depends on the underlying 104.Vt BIO . 105When using a non-blocking socket, nothing is to be done, but 106.Xr select 2 107can be used to check for the required condition. 108When using a buffering 109.Vt BIO , 110like a 111.Vt BIO 112pair, data must be written into or retrieved out of the 113.Vt BIO 114before being able to continue. 115.Sh RETURN VALUES 116The following return values can occur: 117.Bl -tag -width Ds 118.It 0 119The TLS/SSL handshake was not successful but was shut down controlled and 120by the specifications of the TLS/SSL protocol. 121Call 122.Xr SSL_get_error 3 123with the return value 124.Fa ret 125to find out the reason. 126.It 1 127The TLS/SSL handshake was successfully completed, 128and a TLS/SSL connection has been established. 129.It <0 130The TLS/SSL handshake was not successful because either a fatal error occurred 131at the protocol level or a connection failure occurred. 132The shutdown was not clean. 133It can also occur if action is needed to continue the operation for 134non-blocking 135.Vt BIO Ns s . 136Call 137.Xr SSL_get_error 3 138with the return value 139.Fa ret 140to find out the reason. 141.El 142.Sh SEE ALSO 143.Xr BIO_new 3 , 144.Xr ssl 3 , 145.Xr SSL_accept 3 , 146.Xr SSL_connect 3 , 147.Xr SSL_get_error 3 , 148.Xr SSL_set_connect_state 3 149.Sh HISTORY 150.Fn SSL_do_handshake 151first appeared in SSLeay 0.8.0 and has been available since 152.Ox 2.4 . 153