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140 .IX Title "DSA_set_method 3"
141 .TH DSA_set_method 3 "0.9.7a" "2003-02-19" "OpenSSL"
144 DSA_set_default_method, DSA_get_default_method,
145 DSA_set_method, DSA_new_method, DSA_OpenSSL \- select \s-1DSA\s0 method
147 .IX Header "SYNOPSIS"
149 \& #include <openssl/dsa.h>
150 \& #include <openssl/engine.h>
153 \& void DSA_set_default_method(const DSA_METHOD *meth);
156 \& const DSA_METHOD *DSA_get_default_method(void);
159 \& int DSA_set_method(DSA *dsa, const DSA_METHOD *meth);
162 \& DSA *DSA_new_method(ENGINE *engine);
165 \& DSA_METHOD *DSA_OpenSSL(void);
168 .IX Header "DESCRIPTION"
169 A \fB\s-1DSA_METHOD\s0\fR specifies the functions that OpenSSL uses for \s-1DSA\s0
170 operations. By modifying the method, alternative implementations
171 such as hardware accelerators may be used. \s-1IMPORTANT:\s0 See the \s-1NOTES\s0 section for
172 important information about how these \s-1DSA\s0 \s-1API\s0 functions are affected by the use
173 of \fB\s-1ENGINE\s0\fR \s-1API\s0 calls.
175 Initially, the default \s-1DSA_METHOD\s0 is the OpenSSL internal implementation,
176 as returned by \fIDSA_OpenSSL()\fR.
178 \&\fIDSA_set_default_method()\fR makes \fBmeth\fR the default method for all \s-1DSA\s0
179 structures created later. \fB\s-1NB\s0\fR: This is true only whilst no \s-1ENGINE\s0 has
180 been set as a default for \s-1DSA\s0, so this function is no longer recommended.
182 \&\fIDSA_get_default_method()\fR returns a pointer to the current default
183 \&\s-1DSA_METHOD\s0. However, the meaningfulness of this result is dependant on
184 whether the \s-1ENGINE\s0 \s-1API\s0 is being used, so this function is no longer
187 \&\fIDSA_set_method()\fR selects \fBmeth\fR to perform all operations using the key
188 \&\fBrsa\fR. This will replace the \s-1DSA_METHOD\s0 used by the \s-1DSA\s0 key and if the
189 previous method was supplied by an \s-1ENGINE\s0, the handle to that \s-1ENGINE\s0 will
190 be released during the change. It is possible to have \s-1DSA\s0 keys that only
191 work with certain \s-1DSA_METHOD\s0 implementations (eg. from an \s-1ENGINE\s0 module
192 that supports embedded hardware-protected keys), and in such cases
193 attempting to change the \s-1DSA_METHOD\s0 for the key can have unexpected
196 \&\fIDSA_new_method()\fR allocates and initializes a \s-1DSA\s0 structure so that \fBengine\fR
197 will be used for the \s-1DSA\s0 operations. If \fBengine\fR is \s-1NULL\s0, the default engine
198 for \s-1DSA\s0 operations is used, and if no default \s-1ENGINE\s0 is set, the \s-1DSA_METHOD\s0
199 controlled by \fIDSA_set_default_method()\fR is used.
200 .SH "THE DSA_METHOD STRUCTURE"
201 .IX Header "THE DSA_METHOD STRUCTURE"
204 /* name of the implementation */
209 \& DSA_SIG *(*dsa_do_sign)(const unsigned char *dgst, int dlen,
213 \& /* pre-compute k^-1 and r */
214 \& int (*dsa_sign_setup)(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
219 \& int (*dsa_do_verify)(const unsigned char *dgst, int dgst_len,
220 \& DSA_SIG *sig, DSA *dsa);
223 \& /* compute rr = a1^p1 * a2^p2 mod m (May be NULL for some
224 \& implementations) */
225 \& int (*dsa_mod_exp)(DSA *dsa, BIGNUM *rr, BIGNUM *a1, BIGNUM *p1,
226 \& BIGNUM *a2, BIGNUM *p2, BIGNUM *m,
227 \& BN_CTX *ctx, BN_MONT_CTX *in_mont);
230 \& /* compute r = a ^ p mod m (May be NULL for some implementations) */
231 \& int (*bn_mod_exp)(DSA *dsa, BIGNUM *r, BIGNUM *a,
232 \& const BIGNUM *p, const BIGNUM *m,
233 \& BN_CTX *ctx, BN_MONT_CTX *m_ctx);
236 \& /* called at DSA_new */
237 \& int (*init)(DSA *DSA);
240 \& /* called at DSA_free */
241 \& int (*finish)(DSA *DSA);
247 \& char *app_data; /* ?? */
253 .IX Header "RETURN VALUES"
254 \&\fIDSA_OpenSSL()\fR and \fIDSA_get_default_method()\fR return pointers to the respective
255 \&\fB\s-1DSA_METHOD\s0\fRs.
257 \&\fIDSA_set_default_method()\fR returns no value.
259 \&\fIDSA_set_method()\fR returns non-zero if the provided \fBmeth\fR was successfully set as
260 the method for \fBdsa\fR (including unloading the \s-1ENGINE\s0 handle if the previous
261 method was supplied by an \s-1ENGINE\s0).
263 \&\fIDSA_new_method()\fR returns \s-1NULL\s0 and sets an error code that can be
264 obtained by ERR_get_error(3) if the allocation
265 fails. Otherwise it returns a pointer to the newly allocated structure.
268 As of version 0.9.7, \s-1DSA_METHOD\s0 implementations are grouped together with other
269 algorithmic APIs (eg. \s-1RSA_METHOD\s0, \s-1EVP_CIPHER\s0, etc) in \fB\s-1ENGINE\s0\fR modules. If a
270 default \s-1ENGINE\s0 is specified for \s-1DSA\s0 functionality using an \s-1ENGINE\s0 \s-1API\s0 function,
271 that will override any \s-1DSA\s0 defaults set using the \s-1DSA\s0 \s-1API\s0 (ie.
272 \&\fIDSA_set_default_method()\fR). For this reason, the \s-1ENGINE\s0 \s-1API\s0 is the recommended way
273 to control default implementations for use in \s-1DSA\s0 and other cryptographic
276 .IX Header "SEE ALSO"
280 \&\fIDSA_set_default_method()\fR, \fIDSA_get_default_method()\fR, \fIDSA_set_method()\fR,
281 \&\fIDSA_new_method()\fR and \fIDSA_OpenSSL()\fR were added in OpenSSL 0.9.4.
283 \&\fIDSA_set_default_openssl_method()\fR and \fIDSA_get_default_openssl_method()\fR replaced
284 \&\fIDSA_set_default_method()\fR and \fIDSA_get_default_method()\fR respectively, and
285 \&\fIDSA_set_method()\fR and \fIDSA_new_method()\fR were altered to use \fB\s-1ENGINE\s0\fRs rather than
286 \&\fB\s-1DSA_METHOD\s0\fRs during development of the engine version of OpenSSL 0.9.6. For
287 0.9.7, the handling of defaults in the \s-1ENGINE\s0 \s-1API\s0 was restructured so that this
288 change was reversed, and behaviour of the other functions resembled more closely
289 the previous behaviour. The behaviour of defaults in the \s-1ENGINE\s0 \s-1API\s0 now
290 transparently overrides the behaviour of defaults in the \s-1DSA\s0 \s-1API\s0 without
291 requiring changing these function prototypes.