1.\" $OpenBSD: DH_set_method.3,v 1.9 2023/11/19 10:34:26 tb 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, 2002, 2007 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. 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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: November 19 2023 $ 52.Dt DH_SET_METHOD 3 53.Os 54.Sh NAME 55.Nm DH_set_default_method , 56.Nm DH_get_default_method , 57.Nm DH_set_method , 58.Nm DH_new_method , 59.Nm DH_OpenSSL 60.Nd select DH method 61.Sh SYNOPSIS 62.In openssl/dh.h 63.Ft void 64.Fo DH_set_default_method 65.Fa "const DH_METHOD *meth" 66.Fc 67.Ft const DH_METHOD * 68.Fo DH_get_default_method 69.Fa void 70.Fc 71.Ft int 72.Fo DH_set_method 73.Fa "DH *dh" 74.Fa "const DH_METHOD *meth" 75.Fc 76.Ft DH * 77.Fo DH_new_method 78.Fa "ENGINE *engine" 79.Fc 80.Ft const DH_METHOD * 81.Fo DH_OpenSSL 82.Fa void 83.Fc 84.Sh DESCRIPTION 85A 86.Vt DH_METHOD 87object contains pointers to the functions 88used for Diffie-Hellman operations. 89By default, the internal implementation returned by 90.Fn DH_OpenSSL 91is used. 92By selecting another method, alternative implementations 93such as hardware accelerators may be used. 94.Pp 95.Fn DH_set_default_method 96selects 97.Fa meth 98as the default method for all 99.Vt DH 100structures created later. 101.Pp 102.Fn DH_get_default_method 103returns a pointer to the current default method. 104.Pp 105.Fn DH_set_method 106selects 107.Fa meth 108to perform all operations using the key 109.Fa dh . 110This replaces the 111.Vt DH_METHOD 112used by the 113.Fa dh 114key. 115It is possible to have 116.Vt DH 117keys that only work with certain 118.Vt DH_METHOD 119implementations, 120and in such cases attempting to change the 121.Vt DH_METHOD 122for the key can have unexpected results. 123.Pp 124.Fn DH_new_method 125allocates and initializes a 126.Vt DH 127structure. 128The 129.Fa engine 130argument is ignored and 131the default method controlled by 132.Fn DH_set_default_method 133is used. 134.Pp 135The 136.Vt DH_METHOD 137structure is defined as follows: 138.Bd -literal 139typedef struct dh_meth_st 140{ 141 /* name of the implementation */ 142 const char *name; 143 144 /* generate private and public DH values for key agreement */ 145 int (*generate_key)(DH *dh); 146 147 /* compute shared secret */ 148 int (*compute_key)(unsigned char *key, BIGNUM *pub_key, DH *dh); 149 150 /* compute r = a ^ p mod m (May be NULL for some implementations) */ 151 int (*bn_mod_exp)(DH *dh, BIGNUM *r, BIGNUM *a, const BIGNUM *p, 152 const BIGNUM *m, BN_CTX *ctx, 153 BN_MONT_CTX *m_ctx); 154 155 /* called at DH_new */ 156 int (*init)(DH *dh); 157 158 /* called at DH_free */ 159 int (*finish)(DH *dh); 160 161 int flags; 162 163 char *app_data; /* ?? */ 164 165} DH_METHOD; 166.Ed 167.Sh RETURN VALUES 168.Fn DH_OpenSSL 169and 170.Fn DH_get_default_method 171return pointers to the respective 172.Vt DH_METHOD . 173.Pp 174.Fn DH_set_method 175returns 1 on success or 0 on failure. 176Currently, it cannot fail. 177.Pp 178.Fn DH_new_method 179returns 180.Dv NULL 181and sets an error code that can be obtained by 182.Xr ERR_get_error 3 183if the allocation fails. 184Otherwise it returns a pointer to the newly allocated structure. 185.Sh SEE ALSO 186.Xr DH_new 3 187.Sh HISTORY 188.Fn DH_set_default_method , 189.Fn DH_get_default_method , 190.Fn DH_set_method , 191.Fn DH_new_method 192and 193.Fn DH_OpenSSL 194first appeared in OpenSSL 0.9.5 and have been available since 195.Ox 2.7 . 196