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Editing: DH_generate_parameters.3
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Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "NAME" DH_generate_parameters_ex, DH_generate_parameters, DH_check \- generate and check Diffie\-Hellman parameters .SH "SYNOPSIS" .IX Header "SYNOPSIS" .Vb 1 \& #include <openssl/dh.h> \& \& int DH_generate_parameters_ex(DH *dh, int prime_len,int generator, BN_GENCB *cb); \& \& int DH_check(DH *dh, int *codes); .Ve .PP Deprecated: .PP .Vb 2 \& DH *DH_generate_parameters(int prime_len, int generator, \& void (*callback)(int, int, void *), void *cb_arg); .Ve .SH "DESCRIPTION" .IX Header "DESCRIPTION" \&\fBDH_generate_parameters_ex()\fR generates Diffie-Hellman parameters that can be shared among a group of users, and stores them in the provided \fB\s-1DH\s0\fR structure. The pseudo-random number generator must be seeded prior to calling \fBDH_generate_parameters()\fR. .PP \&\fBprime_len\fR is the length in bits of the safe prime to be generated. \&\fBgenerator\fR is a small number > 1, typically 2 or 5. .PP A callback function may be used to provide feedback about the progress of the key generation. If \fBcb\fR is not \fB\s-1NULL\s0\fR, it will be called as described in \fBBN_generate_prime\fR\|(3) while a random prime number is generated, and when a prime has been found, \fBBN_GENCB_call(cb, 3, 0)\fR is called. See \fBBN_generate_prime\fR\|(3) for information on the \fBBN_GENCB_call()\fR function. .PP \&\fBDH_check()\fR validates Diffie-Hellman parameters. It checks that \fBp\fR is a safe prime, and that \fBg\fR is a suitable generator. In the case of an error, the bit flags \s-1DH_CHECK_P_NOT_SAFE_PRIME\s0 or \&\s-1DH_NOT_SUITABLE_GENERATOR\s0 are set in \fB*codes\fR. \&\s-1DH_UNABLE_TO_CHECK_GENERATOR\s0 is set if the generator cannot be checked, i.e. it does not equal 2 or 5. .SH "RETURN VALUES" .IX Header "RETURN VALUES" \&\fBDH_generate_parameters_ex()\fR and \fBDH_check()\fR return 1 if the check could be performed, 0 otherwise. .PP \&\fBDH_generate_parameters()\fR (deprecated) returns a pointer to the \s-1DH\s0 structure, or \&\s-1NULL\s0 if the parameter generation fails. .PP The error codes can be obtained by \fBERR_get_error\fR\|(3). .SH "NOTES" .IX Header "NOTES" \&\fBDH_generate_parameters_ex()\fR and \fBDH_generate_parameters()\fR may run for several hours before finding a suitable prime. .PP The parameters generated by \fBDH_generate_parameters_ex()\fR and \fBDH_generate_parameters()\fR are not to be used in signature schemes. .SH "BUGS" .IX Header "BUGS" If \fBgenerator\fR is not 2 or 5, \fBdh\->g\fR=\fBgenerator\fR is not a usable generator. .SH "SEE ALSO" .IX Header "SEE ALSO" \&\fBdh\fR\|(3), \fBERR_get_error\fR\|(3), \fBrand\fR\|(3), \&\fBDH_free\fR\|(3) .SH "HISTORY" .IX Header "HISTORY" \&\fBDH_check()\fR is available in all versions of SSLeay and OpenSSL. The \fBcb_arg\fR argument to \fBDH_generate_parameters()\fR was added in SSLeay 0.9.0. .PP In versions before OpenSSL 0.9.5, \s-1DH_CHECK_P_NOT_STRONG_PRIME\s0 is used instead of \s-1DH_CHECK_P_NOT_SAFE_PRIME.\s0
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