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135 .IX Title "DH_generate_parameters 3"
136 .TH DH_generate_parameters 3 "2016-05-03" "1.0.2h" "OpenSSL"
137 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
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142 DH_generate_parameters_ex, DH_generate_parameters,
143 DH_check \- generate and check Diffie\-Hellman parameters
145 .IX Header "SYNOPSIS"
147 \& #include <openssl/dh.h>
149 \& int DH_generate_parameters_ex(DH *dh, int prime_len,int generator, BN_GENCB *cb);
151 \& int DH_check(DH *dh, int *codes);
157 \& DH *DH_generate_parameters(int prime_len, int generator,
158 \& void (*callback)(int, int, void *), void *cb_arg);
161 .IX Header "DESCRIPTION"
162 \&\fIDH_generate_parameters_ex()\fR generates Diffie-Hellman parameters that can
163 be shared among a group of users, and stores them in the provided \fB\s-1DH\s0\fR
164 structure. The pseudo-random number generator must be
165 seeded prior to calling \fIDH_generate_parameters()\fR.
167 \&\fBprime_len\fR is the length in bits of the safe prime to be generated.
168 \&\fBgenerator\fR is a small number > 1, typically 2 or 5.
170 A callback function may be used to provide feedback about the progress
171 of the key generation. If \fBcb\fR is not \fB\s-1NULL\s0\fR, it will be
172 called as described in \fIBN_generate_prime\fR\|(3) while a random prime
173 number is generated, and when a prime has been found, \fBBN_GENCB_call(cb, 3, 0)\fR
174 is called. See \fIBN_generate_prime\fR\|(3) for information on
175 the \fIBN_GENCB_call()\fR function.
177 \&\fIDH_check()\fR validates Diffie-Hellman parameters. It checks that \fBp\fR is
178 a safe prime, and that \fBg\fR is a suitable generator. In the case of an
179 error, the bit flags \s-1DH_CHECK_P_NOT_SAFE_PRIME\s0 or
180 \&\s-1DH_NOT_SUITABLE_GENERATOR\s0 are set in \fB*codes\fR.
181 \&\s-1DH_UNABLE_TO_CHECK_GENERATOR\s0 is set if the generator cannot be
182 checked, i.e. it does not equal 2 or 5.
184 .IX Header "RETURN VALUES"
185 \&\fIDH_generate_parameters_ex()\fR and \fIDH_check()\fR return 1 if the check could be
186 performed, 0 otherwise.
188 \&\fIDH_generate_parameters()\fR (deprecated) returns a pointer to the \s-1DH\s0 structure, or
189 \&\s-1NULL\s0 if the parameter generation fails.
191 The error codes can be obtained by \fIERR_get_error\fR\|(3).
194 \&\fIDH_generate_parameters_ex()\fR and \fIDH_generate_parameters()\fR may run for several
195 hours before finding a suitable prime.
197 The parameters generated by \fIDH_generate_parameters_ex()\fR and \fIDH_generate_parameters()\fR
198 are not to be used in signature schemes.
201 If \fBgenerator\fR is not 2 or 5, \fBdh\->g\fR=\fBgenerator\fR is not
204 .IX Header "SEE ALSO"
205 \&\fIdh\fR\|(3), \fIERR_get_error\fR\|(3), \fIrand\fR\|(3),
209 \&\fIDH_check()\fR is available in all versions of SSLeay and OpenSSL.
210 The \fBcb_arg\fR argument to \fIDH_generate_parameters()\fR was added in SSLeay 0.9.0.
212 In versions before OpenSSL 0.9.5, \s-1DH_CHECK_P_NOT_STRONG_PRIME\s0 is used
213 instead of \s-1DH_CHECK_P_NOT_SAFE_PRIME.\s0