1.\" $OpenBSD: DSA_set_method.3,v 1.11 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 DSA_SET_METHOD 3 53.Os 54.Sh NAME 55.Nm DSA_set_default_method , 56.Nm DSA_get_default_method , 57.Nm DSA_set_method , 58.Nm DSA_new_method , 59.Nm DSA_OpenSSL 60.Nd select DSA method 61.Sh SYNOPSIS 62.In openssl/dsa.h 63.Ft void 64.Fo DSA_set_default_method 65.Fa "const DSA_METHOD *meth" 66.Fc 67.Ft const DSA_METHOD * 68.Fn DSA_get_default_method void 69.Ft int 70.Fo DSA_set_method 71.Fa "DSA *dsa" 72.Fa "const DSA_METHOD *meth" 73.Fc 74.Ft DSA * 75.Fo DSA_new_method 76.Fa "ENGINE *engine" 77.Fc 78.Ft DSA_METHOD * 79.Fn DSA_OpenSSL void 80.Sh DESCRIPTION 81A 82.Vt DSA_METHOD 83object contains pointers to the functions used for DSA operations. 84By default, the internal implementation returned by 85.Fn DSA_OpenSSL 86is used. 87By selecting another method, alternative implementations 88such as hardware accelerators may be used. 89.Pp 90.Fn DSA_set_default_method 91selects 92.Fa meth 93as the default method for all 94.Vt DSA 95structures created later. 96.Pp 97.Fn DSA_get_default_method 98returns a pointer to the current default method. 99.Pp 100.Fn DSA_set_method 101selects 102.Fa meth 103to perform all operations using the key 104.Fa dsa . 105This replaces the 106.Vt DSA_METHOD 107used by the DSA key. 108It is possible to have DSA keys that only work with certain 109.Vt DSA_METHOD 110implementations, 111and in such cases attempting to change the 112.Vt DSA_METHOD 113for the key can have unexpected results. 114.Pp 115.Fn DSA_new_method 116allocates and initializes a 117.Vt DSA 118structure. 119The 120.Fa engine 121argument is ignored and 122the default method controlled by 123.Fn DSA_set_default_method 124is used. 125.Pp 126The 127.Vt DSA_METHOD 128structure is defined as follows: 129.Bd -literal 130struct 131{ 132 /* name of the implementation */ 133 const char *name; 134 135 /* sign */ 136 DSA_SIG *(*dsa_do_sign)(const unsigned char *dgst, int dlen, 137 DSA *dsa); 138 139 /* pre-compute k^-1 and r */ 140 int (*dsa_sign_setup)(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, 141 BIGNUM **rp); 142 143 /* verify */ 144 int (*dsa_do_verify)(const unsigned char *dgst, int dgst_len, 145 DSA_SIG *sig, DSA *dsa); 146 147 /* compute rr = a1^p1 * a2^p2 mod m (May be NULL for some 148 implementations) */ 149 int (*dsa_mod_exp)(DSA *dsa, BIGNUM *rr, BIGNUM *a1, BIGNUM *p1, 150 BIGNUM *a2, BIGNUM *p2, BIGNUM *m, 151 BN_CTX *ctx, BN_MONT_CTX *in_mont); 152 153 /* compute r = a ^ p mod m (May be NULL for some implementations) */ 154 int (*bn_mod_exp)(DSA *dsa, BIGNUM *r, BIGNUM *a, 155 const BIGNUM *p, const BIGNUM *m, 156 BN_CTX *ctx, BN_MONT_CTX *m_ctx); 157 158 /* called at DSA_new */ 159 int (*init)(DSA *DSA); 160 161 /* called at DSA_free */ 162 int (*finish)(DSA *DSA); 163 164 int flags; 165 166 char *app_data; /* ?? */ 167 168} DSA_METHOD; 169.Ed 170.Sh RETURN VALUES 171.Fn DSA_OpenSSL 172and 173.Fn DSA_get_default_method 174return pointers to the respective 175.Vt DSA_METHOD . 176.Pp 177.Fn DSA_set_method 178returns 1 on success or 0 on failure. 179Currently, it cannot fail. 180.Pp 181.Fn DSA_new_method 182returns 183.Dv NULL 184and sets an error code that can be obtained by 185.Xr ERR_get_error 3 186if the allocation fails. 187Otherwise it returns a pointer to the newly allocated structure. 188.Sh SEE ALSO 189.Xr DSA_meth_new 3 , 190.Xr DSA_new 3 191.Sh HISTORY 192.Fn DSA_set_default_method , 193.Fn DSA_get_default_method , 194.Fn DSA_set_method , 195.Fn DSA_new_method , 196and 197.Fn DSA_OpenSSL 198first appeared in OpenSSL 0.9.5 and have been available since 199.Ox 2.7 . 200