1.\" $OpenBSD: DSA_set_method.3,v 1.6 2016/12/10 22:47:49 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, 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: December 10 2016 $ 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.In openssl/engine.h 64.Ft void 65.Fo DSA_set_default_method 66.Fa "const DSA_METHOD *meth" 67.Fc 68.Ft const DSA_METHOD * 69.Fn DSA_get_default_method void 70.Ft int 71.Fo DSA_set_method 72.Fa "DSA *dsa" 73.Fa "const DSA_METHOD *meth" 74.Fc 75.Ft DSA * 76.Fo DSA_new_method 77.Fa "ENGINE *engine" 78.Fc 79.Ft DSA_METHOD * 80.Fn DSA_OpenSSL void 81.Sh DESCRIPTION 82A 83.Vt DSA_METHOD 84specifies the functions that OpenSSL uses for DSA operations. 85By modifying the method, alternative implementations such as hardware 86accelerators may be used. 87See the 88.Sx CAVEATS 89section for how these DSA API functions are affected by the use of 90.Xr engine 3 91API calls. 92.Pp 93Initially, the default 94.Vt DSA_METHOD 95is the OpenSSL internal implementation, as returned by 96.Fn DSA_OpenSSL . 97.Pp 98.Fn DSA_set_default_method 99makes 100.Fa meth 101the default method for all 102.Vt DSA 103structures created later. 104.Sy Note : 105this is true only whilst no 106.Vt ENGINE 107has been set as a default for DSA, so this function is no longer 108recommended. 109.Pp 110.Fn DSA_get_default_method 111returns a pointer to the current default 112.Vt DSA_METHOD . 113However, the meaningfulness of this result is dependent on whether the 114.Xr engine 3 115API is being used, so this function is no longer recommended. 116.Pp 117.Fn DSA_set_method 118selects 119.Fa meth 120to perform all operations using the key 121.Fa dsa . 122This will replace the 123.Vt DSA_METHOD 124used by the DSA key and if the previous method was supplied by an 125.Vt ENGINE , 126the handle to that 127.Vt ENGINE 128will be released during the change. 129It is possible to have DSA keys that only work with certain 130.Vt DSA_METHOD 131implementations (e.g. from an 132.Vt ENGINE 133module that supports embedded hardware-protected keys), 134and in such cases attempting to change the 135.Vt DSA_METHOD 136for the key can have unexpected results. 137.Pp 138.Fn DSA_new_method 139allocates and initializes a 140.Vt DSA 141structure so that 142.Fa engine 143will be used for the DSA operations. 144If 145.Fa engine 146is 147.Dv NULL , 148the default engine for DSA operations is used and, if no 149default 150.Vt ENGINE 151is set, the 152.Vt DSA_METHOD 153controlled by 154.Fn DSA_set_default_method 155is used. 156.Pp 157The 158.Vt DSA_METHOD 159structure is defined as follows: 160.Bd -literal 161struct 162{ 163 /* name of the implementation */ 164 const char *name; 165 166 /* sign */ 167 DSA_SIG *(*dsa_do_sign)(const unsigned char *dgst, int dlen, 168 DSA *dsa); 169 170 /* pre-compute k^-1 and r */ 171 int (*dsa_sign_setup)(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, 172 BIGNUM **rp); 173 174 /* verify */ 175 int (*dsa_do_verify)(const unsigned char *dgst, int dgst_len, 176 DSA_SIG *sig, DSA *dsa); 177 178 /* compute rr = a1^p1 * a2^p2 mod m (May be NULL for some 179 implementations) */ 180 int (*dsa_mod_exp)(DSA *dsa, BIGNUM *rr, BIGNUM *a1, BIGNUM *p1, 181 BIGNUM *a2, BIGNUM *p2, BIGNUM *m, 182 BN_CTX *ctx, BN_MONT_CTX *in_mont); 183 184 /* compute r = a ^ p mod m (May be NULL for some implementations) */ 185 int (*bn_mod_exp)(DSA *dsa, BIGNUM *r, BIGNUM *a, 186 const BIGNUM *p, const BIGNUM *m, 187 BN_CTX *ctx, BN_MONT_CTX *m_ctx); 188 189 /* called at DSA_new */ 190 int (*init)(DSA *DSA); 191 192 /* called at DSA_free */ 193 int (*finish)(DSA *DSA); 194 195 int flags; 196 197 char *app_data; /* ?? */ 198 199} DSA_METHOD; 200.Ed 201.Sh RETURN VALUES 202.Fn DSA_OpenSSL 203and 204.Fn DSA_get_default_method 205return pointers to the respective 206.Vt DSA_METHOD Ns s . 207.Pp 208.Fn DSA_set_method 209returns non-zero if the provided 210.Fa meth 211was successfully set as the method for 212.Fa dsa 213(including unloading the 214.Vt ENGINE 215handle if the previous method was supplied by an 216.Vt ENGINE ) . 217.Pp 218.Fn DSA_new_method 219returns 220.Dv NULL 221and sets an error code that can be obtained by 222.Xr ERR_get_error 3 223if the allocation fails. 224Otherwise it returns a pointer to the newly allocated structure. 225.Sh SEE ALSO 226.Xr DSA_new 3 227.Sh HISTORY 228.Fn DSA_set_default_method , 229.Fn DSA_get_default_method , 230.Fn DSA_set_method , 231.Fn DSA_new_method , 232and 233.Fn DSA_OpenSSL 234were added in OpenSSL 0.9.4. 235.Sh CAVEATS 236As of version 0.9.7, DSA_METHOD implementations are grouped together 237with other algorithmic APIs (e.g. RSA_METHOD, EVP_CIPHER) in 238.Vt ENGINE 239modules. 240If a default 241.Vt ENGINE 242is specified for DSA functionality using an 243.Xr engine 3 244API function, that will override any DSA defaults set using the DSA API 245.Pq i.e. DSA_set_default_method . 246For this reason, the 247.Xr engine 3 248API is the recommended way to control default implementations for 249use in DSA and other cryptographic algorithms. 250