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126 .IX Title "DH_generate_parameters 3"
127 .TH DH_generate_parameters 3 "2007-10-24" "0.9.8g" "OpenSSL"
128 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
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133 DH_generate_parameters, DH_check \- generate and check Diffie\-Hellman parameters
135 .IX Header "SYNOPSIS"
137 \& #include <openssl/dh.h>
139 \& DH *DH_generate_parameters(int prime_len, int generator,
140 \& void (*callback)(int, int, void *), void *cb_arg);
142 \& int DH_check(DH *dh, int *codes);
145 .IX Header "DESCRIPTION"
146 \&\fIDH_generate_parameters()\fR generates Diffie-Hellman parameters that can
147 be shared among a group of users, and returns them in a newly
148 allocated \fB\s-1DH\s0\fR structure. The pseudo-random number generator must be
149 seeded prior to calling \fIDH_generate_parameters()\fR.
151 \&\fBprime_len\fR is the length in bits of the safe prime to be generated.
152 \&\fBgenerator\fR is a small number > 1, typically 2 or 5.
154 A callback function may be used to provide feedback about the progress
155 of the key generation. If \fBcallback\fR is not \fB\s-1NULL\s0\fR, it will be
156 called as described in \fIBN_generate_prime\fR\|(3) while a random prime
157 number is generated, and when a prime has been found, \fBcallback(3,
158 0, cb_arg)\fR is called.
160 \&\fIDH_check()\fR validates Diffie-Hellman parameters. It checks that \fBp\fR is
161 a safe prime, and that \fBg\fR is a suitable generator. In the case of an
162 error, the bit flags \s-1DH_CHECK_P_NOT_SAFE_PRIME\s0 or
163 \&\s-1DH_NOT_SUITABLE_GENERATOR\s0 are set in \fB*codes\fR.
164 \&\s-1DH_UNABLE_TO_CHECK_GENERATOR\s0 is set if the generator cannot be
165 checked, i.e. it does not equal 2 or 5.
167 .IX Header "RETURN VALUES"
168 \&\fIDH_generate_parameters()\fR returns a pointer to the \s-1DH\s0 structure, or
169 \&\s-1NULL\s0 if the parameter generation fails. The error codes can be
170 obtained by \fIERR_get_error\fR\|(3).
172 \&\fIDH_check()\fR returns 1 if the check could be performed, 0 otherwise.
175 \&\fIDH_generate_parameters()\fR may run for several hours before finding a
178 The parameters generated by \fIDH_generate_parameters()\fR are not to be
179 used in signature schemes.
182 If \fBgenerator\fR is not 2 or 5, \fBdh\->g\fR=\fBgenerator\fR is not
185 .IX Header "SEE ALSO"
186 \&\fIdh\fR\|(3), \fIERR_get_error\fR\|(3), \fIrand\fR\|(3),
190 \&\fIDH_check()\fR is available in all versions of SSLeay and OpenSSL.
191 The \fBcb_arg\fR argument to \fIDH_generate_parameters()\fR was added in SSLeay 0.9.0.
193 In versions before OpenSSL 0.9.5, \s-1DH_CHECK_P_NOT_STRONG_PRIME\s0 is used
194 instead of \s-1DH_CHECK_P_NOT_SAFE_PRIME\s0.