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135 .IX Title "DSA_generate_parameters 3"
136 .TH DSA_generate_parameters 3 "2016-09-26" "1.0.2j" "OpenSSL"
137 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
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142 DSA_generate_parameters_ex, DSA_generate_parameters \- generate DSA parameters
144 .IX Header "SYNOPSIS"
146 \& #include <openssl/dsa.h>
148 \& int DSA_generate_parameters_ex(DSA *dsa, int bits,
149 \& const unsigned char *seed,int seed_len,
150 \& int *counter_ret, unsigned long *h_ret, BN_GENCB *cb);
156 \& DSA *DSA_generate_parameters(int bits, unsigned char *seed,
157 \& int seed_len, int *counter_ret, unsigned long *h_ret,
158 \& void (*callback)(int, int, void *), void *cb_arg);
161 .IX Header "DESCRIPTION"
162 \&\fIDSA_generate_parameters_ex()\fR generates primes p and q and a generator g
163 for use in the \s-1DSA\s0 and stores the result in \fBdsa\fR.
165 \&\fBbits\fR is the length of the prime to be generated; the \s-1DSS\s0 allows a
166 maximum of 1024 bits.
168 If \fBseed\fR is \fB\s-1NULL\s0\fR or \fBseed_len\fR < 20, the primes will be
169 generated at random. Otherwise, the seed is used to generate
170 them. If the given seed does not yield a prime q, a new random
173 \&\fIDSA_generate_parameters_ex()\fR places the iteration count in
174 *\fBcounter_ret\fR and a counter used for finding a generator in
175 *\fBh_ret\fR, unless these are \fB\s-1NULL\s0\fR.
177 A callback function may be used to provide feedback about the progress
178 of the key generation. If \fBcb\fR is not \fB\s-1NULL\s0\fR, it will be
179 called as shown below. For information on the \s-1BN_GENCB\s0 structure and the
180 BN_GENCB_call function discussed below, refer to
181 \&\fIBN_generate_prime\fR\|(3).
183 When a candidate for q is generated, \fBBN_GENCB_call(cb, 0, m++)\fR is called
184 (m is 0 for the first candidate).
186 When a candidate for q has passed a test by trial division,
187 \&\fBBN_GENCB_call(cb, 1, \-1)\fR is called.
188 While a candidate for q is tested by Miller-Rabin primality tests,
189 \&\fBBN_GENCB_call(cb, 1, i)\fR is called in the outer loop
190 (once for each witness that confirms that the candidate may be prime);
191 i is the loop counter (starting at 0).
193 When a prime q has been found, \fBBN_GENCB_call(cb, 2, 0)\fR and
194 \&\fBBN_GENCB_call(cb, 3, 0)\fR are called.
196 Before a candidate for p (other than the first) is generated and tested,
197 \&\fBBN_GENCB_call(cb, 0, counter)\fR is called.
199 When a candidate for p has passed the test by trial division,
200 \&\fBBN_GENCB_call(cb, 1, \-1)\fR is called.
201 While it is tested by the Miller-Rabin primality test,
202 \&\fBBN_GENCB_call(cb, 1, i)\fR is called in the outer loop
203 (once for each witness that confirms that the candidate may be prime).
204 i is the loop counter (starting at 0).
206 When p has been found, \fBBN_GENCB_call(cb, 2, 1)\fR is called.
208 When the generator has been found, \fBBN_GENCB_call(cb, 3, 1)\fR is called.
210 \&\fIDSA_generate_parameters()\fR (deprecated) works in much the same way as for DSA_generate_parameters_ex, except that no \fBdsa\fR parameter is passed and
211 instead a newly allocated \fB\s-1DSA\s0\fR structure is returned. Additionally \*(L"old
212 style\*(R" callbacks are used instead of the newer \s-1BN_GENCB\s0 based approach.
213 Refer to \fIBN_generate_prime\fR\|(3) for further information.
215 .IX Header "RETURN VALUE"
216 \&\fIDSA_generate_parameters_ex()\fR returns a 1 on success, or 0 otherwise.
218 \&\fIDSA_generate_parameters()\fR returns a pointer to the \s-1DSA\s0 structure, or
219 \&\fB\s-1NULL\s0\fR if the parameter generation fails.
221 The error codes can be obtained by \fIERR_get_error\fR\|(3).
224 Seed lengths > 20 are not supported.
226 .IX Header "SEE ALSO"
227 \&\fIdsa\fR\|(3), \fIERR_get_error\fR\|(3), \fIrand\fR\|(3),
228 \&\fIDSA_free\fR\|(3), \fIBN_generate_prime\fR\|(3)
231 \&\fIDSA_generate_parameters()\fR appeared in SSLeay 0.8. The \fBcb_arg\fR
232 argument was added in SSLeay 0.9.0.
233 In versions up to OpenSSL 0.9.4, \fBcallback(1, ...)\fR was called
234 in the inner loop of the Miller-Rabin test whenever it reached the
235 squaring step (the parameters to \fBcallback\fR did not reveal how many
236 witnesses had been tested); since OpenSSL 0.9.5, \fBcallback(1, ...)\fR
237 is called as in \fIBN_is_prime\fR\|(3), i.e. once for each witness.