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131 .IX Title "DSA_set_method 3"
132 .TH DSA_set_method 3 "2009-07-23" "0.9.8k" "OpenSSL"
133 .SH "NAME"
134 DSA_set_default_method, DSA_get_default_method,
135 DSA_set_method, DSA_new_method, DSA_OpenSSL \- select DSA method
136 .SH "SYNOPSIS"
137 .IX Header "SYNOPSIS"
138 .Vb 2
139 \& #include <openssl/dsa.h>
140 \& #include <openssl/engine.h>
141 .Ve
142 .PP
143 .Vb 1
144 \& void DSA_set_default_method(const DSA_METHOD *meth);
145 .Ve
146 .PP
147 .Vb 1
148 \& const DSA_METHOD *DSA_get_default_method(void);
149 .Ve
150 .PP
151 .Vb 1
152 \& int DSA_set_method(DSA *dsa, const DSA_METHOD *meth);
153 .Ve
154 .PP
155 .Vb 1
156 \& DSA *DSA_new_method(ENGINE *engine);
157 .Ve
158 .PP
159 .Vb 1
160 \& DSA_METHOD *DSA_OpenSSL(void);
161 .Ve
162 .SH "DESCRIPTION"
163 .IX Header "DESCRIPTION"
164 A \fB\s-1DSA_METHOD\s0\fR specifies the functions that OpenSSL uses for \s-1DSA\s0
165 operations. By modifying the method, alternative implementations
166 such as hardware accelerators may be used. \s-1IMPORTANT:\s0 See the \s-1NOTES\s0 section for
167 important information about how these \s-1DSA\s0 \s-1API\s0 functions are affected by the use
168 of \fB\s-1ENGINE\s0\fR \s-1API\s0 calls.
169 .PP
170 Initially, the default \s-1DSA_METHOD\s0 is the OpenSSL internal implementation,
171 as returned by \fIDSA_OpenSSL()\fR.
172 .PP
173 \&\fIDSA_set_default_method()\fR makes \fBmeth\fR the default method for all \s-1DSA\s0
174 structures created later. \fB\s-1NB\s0\fR: This is true only whilst no \s-1ENGINE\s0 has
175 been set as a default for \s-1DSA\s0, so this function is no longer recommended.
176 .PP
177 \&\fIDSA_get_default_method()\fR returns a pointer to the current default
178 \&\s-1DSA_METHOD\s0. However, the meaningfulness of this result is dependent on
179 whether the \s-1ENGINE\s0 \s-1API\s0 is being used, so this function is no longer
180 recommended.
181 .PP
182 \&\fIDSA_set_method()\fR selects \fBmeth\fR to perform all operations using the key
183 \&\fBrsa\fR. This will replace the \s-1DSA_METHOD\s0 used by the \s-1DSA\s0 key and if the
184 previous method was supplied by an \s-1ENGINE\s0, the handle to that \s-1ENGINE\s0 will
185 be released during the change. It is possible to have \s-1DSA\s0 keys that only
186 work with certain \s-1DSA_METHOD\s0 implementations (eg. from an \s-1ENGINE\s0 module
187 that supports embedded hardware-protected keys), and in such cases
188 attempting to change the \s-1DSA_METHOD\s0 for the key can have unexpected
189 results.
190 .PP
191 \&\fIDSA_new_method()\fR allocates and initializes a \s-1DSA\s0 structure so that \fBengine\fR
192 will be used for the \s-1DSA\s0 operations. If \fBengine\fR is \s-1NULL\s0, the default engine
193 for \s-1DSA\s0 operations is used, and if no default \s-1ENGINE\s0 is set, the \s-1DSA_METHOD\s0
194 controlled by \fIDSA_set_default_method()\fR is used.
195 .SH "THE DSA_METHOD STRUCTURE"
196 .IX Header "THE DSA_METHOD STRUCTURE"
197 struct
198 {
199 /* name of the implementation */
200 const char *name;
201 .PP
202 .Vb 3
203 \& /* sign */
204 \& DSA_SIG *(*dsa_do_sign)(const unsigned char *dgst, int dlen,
205 \& DSA *dsa);
206 .Ve
207 .PP
208 .Vb 3
209 \& /* pre-compute k^-1 and r */
210 \& int (*dsa_sign_setup)(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
211 \& BIGNUM **rp);
212 .Ve
213 .PP
214 .Vb 3
215 \& /* verify */
216 \& int (*dsa_do_verify)(const unsigned char *dgst, int dgst_len,
217 \& DSA_SIG *sig, DSA *dsa);
218 .Ve
219 .PP
220 .Vb 5
221 \& /* compute rr = a1^p1 * a2^p2 mod m (May be NULL for some
222 \& implementations) */
223 \& int (*dsa_mod_exp)(DSA *dsa, BIGNUM *rr, BIGNUM *a1, BIGNUM *p1,
224 \& BIGNUM *a2, BIGNUM *p2, BIGNUM *m,
225 \& BN_CTX *ctx, BN_MONT_CTX *in_mont);
226 .Ve
227 .PP
228 .Vb 4
229 \& /* compute r = a ^ p mod m (May be NULL for some implementations) */
230 \& int (*bn_mod_exp)(DSA *dsa, BIGNUM *r, BIGNUM *a,
231 \& const BIGNUM *p, const BIGNUM *m,
232 \& BN_CTX *ctx, BN_MONT_CTX *m_ctx);
233 .Ve
234 .PP
235 .Vb 2
236 \& /* called at DSA_new */
237 \& int (*init)(DSA *DSA);
238 .Ve
239 .PP
240 .Vb 2
241 \& /* called at DSA_free */
242 \& int (*finish)(DSA *DSA);
243 .Ve
244 .PP
245 .Vb 1
246 \& int flags;
247 .Ve
248 .PP
249 .Vb 1
250 \& char *app_data; /* ?? */
251 .Ve
252 .PP
253 .Vb 1
254 \& } DSA_METHOD;
255 .Ve
256 .SH "RETURN VALUES"
257 .IX Header "RETURN VALUES"
258 \&\fIDSA_OpenSSL()\fR and \fIDSA_get_default_method()\fR return pointers to the respective
259 \&\fB\s-1DSA_METHOD\s0\fRs.
260 .PP
261 \&\fIDSA_set_default_method()\fR returns no value.
262 .PP
263 \&\fIDSA_set_method()\fR returns non-zero if the provided \fBmeth\fR was successfully set as
264 the method for \fBdsa\fR (including unloading the \s-1ENGINE\s0 handle if the previous
265 method was supplied by an \s-1ENGINE\s0).
266 .PP
267 \&\fIDSA_new_method()\fR returns \s-1NULL\s0 and sets an error code that can be
268 obtained by \fIERR_get_error\fR\|(3) if the allocation
269 fails. Otherwise it returns a pointer to the newly allocated structure.
270 .SH "NOTES"
271 .IX Header "NOTES"
272 As of version 0.9.7, \s-1DSA_METHOD\s0 implementations are grouped together with other
273 algorithmic APIs (eg. \s-1RSA_METHOD\s0, \s-1EVP_CIPHER\s0, etc) in \fB\s-1ENGINE\s0\fR modules. If a
274 default \s-1ENGINE\s0 is specified for \s-1DSA\s0 functionality using an \s-1ENGINE\s0 \s-1API\s0 function,
275 that will override any \s-1DSA\s0 defaults set using the \s-1DSA\s0 \s-1API\s0 (ie.
276 \&\fIDSA_set_default_method()\fR). For this reason, the \s-1ENGINE\s0 \s-1API\s0 is the recommended way
277 to control default implementations for use in \s-1DSA\s0 and other cryptographic
278 algorithms.
279 .SH "SEE ALSO"
280 .IX Header "SEE ALSO"
281 \&\fIdsa\fR\|(3), \fIDSA_new\fR\|(3)
282 .SH "HISTORY"
283 .IX Header "HISTORY"
284 \&\fIDSA_set_default_method()\fR, \fIDSA_get_default_method()\fR, \fIDSA_set_method()\fR,
285 \&\fIDSA_new_method()\fR and \fIDSA_OpenSSL()\fR were added in OpenSSL 0.9.4.
286 .PP
287 \&\fIDSA_set_default_openssl_method()\fR and \fIDSA_get_default_openssl_method()\fR replaced
288 \&\fIDSA_set_default_method()\fR and \fIDSA_get_default_method()\fR respectively, and
289 \&\fIDSA_set_method()\fR and \fIDSA_new_method()\fR were altered to use \fB\s-1ENGINE\s0\fRs rather than
290 \&\fB\s-1DSA_METHOD\s0\fRs during development of the engine version of OpenSSL 0.9.6. For
291 0.9.7, the handling of defaults in the \s-1ENGINE\s0 \s-1API\s0 was restructured so that this
292 change was reversed, and behaviour of the other functions resembled more closely
293 the previous behaviour. The behaviour of defaults in the \s-1ENGINE\s0 \s-1API\s0 now
294 transparently overrides the behaviour of defaults in the \s-1DSA\s0 \s-1API\s0 without
295 requiring changing these function prototypes.