1.\" $OpenBSD: DH_generate_key.3,v 1.12 2019/08/19 13:08:26 schwarze Exp $ 2.\" OpenSSL b97fdb57 Nov 11 09:33:09 2016 +0100 3.\" 4.\" This file was written by Ulf Moeller <ulf@openssl.org>. 5.\" Copyright (c) 2000 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: August 19 2019 $ 52.Dt DH_GENERATE_KEY 3 53.Os 54.Sh NAME 55.Nm DH_generate_key , 56.Nm DH_compute_key 57.Nd perform Diffie-Hellman key exchange 58.Sh SYNOPSIS 59.In openssl/dh.h 60.Ft int 61.Fo DH_generate_key 62.Fa "DH *dh" 63.Fc 64.Ft int 65.Fo DH_compute_key 66.Fa "unsigned char *key" 67.Fa "BIGNUM *pub_key" 68.Fa "DH *dh" 69.Fc 70.Sh DESCRIPTION 71.Fn DH_generate_key 72performs the first step of a Diffie-Hellman key exchange by generating 73private and public DH values. 74By calling 75.Fn DH_compute_key , 76these are combined with the other party's public value to compute the 77shared key. 78.Pp 79.Fn DH_generate_key 80expects 81.Fa dh 82to contain the shared parameters 83.Sy dh->p 84and 85.Sy dh->g . 86It generates a random private DH value unless 87.Sy dh->priv_key 88is already set, and computes the corresponding public value 89.Sy dh->pub_key , 90which can then be published. 91.Pp 92.Fn DH_compute_key 93computes the shared secret from the private DH value in 94.Fa dh 95and the other party's public value in 96.Fa pub_key 97and stores it in 98.Fa key . 99.Fa key 100must point to 101.Fn DH_size dh 102bytes of memory. 103.Sh RETURN VALUES 104.Fn DH_generate_key 105returns 1 on success, or 0 otherwise. 106.Pp 107.Fn DH_compute_key 108returns the size of the shared secret on success, or -1 on error. 109.Pp 110The error codes can be obtained by 111.Xr ERR_get_error 3 . 112.Sh SEE ALSO 113.Xr DH_get0_key 3 , 114.Xr DH_new 3 , 115.Xr DH_size 3 , 116.Xr ECDH_compute_key 3 117.Sh HISTORY 118.Fn DH_generate_key 119and 120.Fn DH_compute_key 121first appeared in SSLeay 0.5.1 and have been available since 122.Ox 2.4 . 123