1.\" $OpenBSD: SSL_get_client_random.3,v 1.2 2018/03/24 00:55:37 schwarze Exp $ 2.\" full merge up to: OpenSSL e9b77246 Jan 20 19:58:49 2017 +0100 3.\" 4.\" This file was written by Nick Mathewson <nickm@torproject.org> 5.\" Copyright (c) 2015 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 24 2018 $ 52.Dt SSL_GET_CLIENT_RANDOM 3 53.Os 54.Sh NAME 55.Nm SSL_get_client_random , 56.Nm SSL_get_server_random , 57.Nm SSL_SESSION_get_master_key 58.Nd get internal TLS handshake random values and master key 59.Sh SYNOPSIS 60.In openssl/ssl.h 61.Ft size_t 62.Fo SSL_get_client_random 63.Fa "const SSL *ssl" 64.Fa "unsigned char *out" 65.Fa "size_t outlen" 66.Fc 67.Ft size_t 68.Fo SSL_get_server_random 69.Fa "const SSL *ssl" 70.Fa "unsigned char *out" 71.Fa "size_t outlen" 72.Fc 73.Ft size_t 74.Fo SSL_SESSION_get_master_key 75.Fa "const SSL_SESSION *session" 76.Fa "unsigned char *out" 77.Fa "size_t outlen" 78.Fc 79.Sh DESCRIPTION 80.Fn SSL_get_client_random 81extracts the random value that was sent from the client to the server 82during the initial TLS handshake. 83It copies at most 84.Fa outlen 85bytes of this value into the buffer 86.Fa out . 87If 88.Fa outlen 89is zero, nothing is copied. 90.Pp 91.Fn SSL_get_server_random 92behaves the same, but extracts the random value that was sent 93from the server to the client during the initial TLS handshake. 94.Pp 95.Fn SSL_SESSION_get_master_key 96behaves the same, but extracts the master secret used to guarantee the 97security of the TLS session. 98The security of the TLS session depends on keeping the master key 99secret: do not expose it, or any information about it, to anybody. 100To calculate another secret value that depends on the master secret, 101use 102.Xr SSL_export_keying_material 3 103instead. 104.Pp 105All these functions expose internal values from the TLS handshake, 106for use in low-level protocols. 107Avoid using them unless implementing a feature 108that requires access to the internal protocol details. 109.Pp 110Despite the names of 111.Fn SSL_get_client_random 112and 113.Fn SSL_get_server_random , 114they are not random number generators. 115Instead, they return the mostly-random values that were already 116generated and used in the TLS protocol. 117.Pp 118In current versions of the TLS protocols, 119the length of client_random and server_random is always 120.Dv SSL3_RANDOM_SIZE 121bytes. 122Support for other 123.Fa outlen 124arguments is provided for the unlikely event that a future 125version or variant of TLS uses some other length. 126.Pp 127Finally, though the client_random and server_random values are called 128.Dq random , 129many TLS implementations generate four bytes of those values 130based on their view of the current time. 131.Sh RETURN VALUES 132If 133.Fa outlen 134is greater than 0, these functions return the number of bytes 135actually copied, which is less than or equal to 136.Fa outlen . 137If 138.Fa outlen 139is 0, these functions return the maximum number of bytes they would 140copy \(em that is, the length of the underlying field. 141.Sh SEE ALSO 142.Xr ssl 3 , 143.Xr SSL_export_keying_material 3 , 144.Xr SSL_SESSION_get_id 3 , 145.Xr SSL_SESSION_get_time 3 , 146.Xr SSL_SESSION_new 3 147.Sh HISTORY 148These functions first appeared in OpenSSL 1.1.0 149and have been available since 150.Ox 6.3 . 151