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.\" ========================================================================
.\"
.IX Title "DH_GENERATE_PARAMETERS 3"
.TH DH_GENERATE_PARAMETERS 3 "2026-02-04" "1.1.1w" "OpenSSL"
.\" For nroff, turn off justification.  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, DH_check_params, DH_check_ex, DH_check_params_ex, DH_check_pub_key_ex \&\- 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);
\& int DH_check_params(DH *dh, int *codes);
\&
\& int DH_check_ex(const DH *dh);
\& int DH_check_params_ex(const DH *dh);
\& int DH_check_pub_key_ex(const DH *dh, const BIGNUM *pub_key);
.Ve
.PP
Deprecated:
.PP
.Vb 4
\& #if OPENSSL_API_COMPAT < 0x00908000L
\& DH *DH_generate_parameters(int prime_len, int generator,
\&                            void (*callback)(int, int, void *), void *cb_arg);
\& #endif
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fIDH_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 before calling it.
The parameters generated by \fIDH_generate_parameters_ex()\fR should not be used in
signature schemes.
.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 \fIBN_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 \fIBN_generate_prime_ex\fR\|(3) for information on
the \fIBN_GENCB_call()\fR function.
.PP
\&\fIDH_generate_parameters()\fR is similar to \fIDH_generate_prime_ex()\fR but
expects an old-style callback function; see
\&\fIBN_generate_prime\fR\|(3) for information on the old-style callback.
.PP
\&\fIDH_check_params()\fR confirms that the \fBp\fR and \fBg\fR are likely enough to
be valid.
This is a lightweight check, if a more thorough check is needed, use
\&\fIDH_check()\fR.
The value of \fB*codes\fR is updated with any problems found.
If \fB*codes\fR is zero then no problems were found, otherwise the
following bits may be set:
.IP "\s-1DH_CHECK_P_NOT_PRIME\s0" 4
.IX Item "DH_CHECK_P_NOT_PRIME"
The parameter \fBp\fR has been determined to not being an odd prime.
Note that the lack of this bit doesn't guarantee that \fBp\fR is a
prime.
.IP "\s-1DH_NOT_SUITABLE_GENERATOR\s0" 4
.IX Item "DH_NOT_SUITABLE_GENERATOR"
The generator \fBg\fR is not suitable.
Note that the lack of this bit doesn't guarantee that \fBg\fR is
suitable, unless \fBp\fR is known to be a strong prime.
.IP "\s-1DH_MODULUS_TOO_LARGE\s0" 4
.IX Item "DH_MODULUS_TOO_LARGE"
The modulus is too large.
.PP
\&\fIDH_check()\fR confirms that the Diffie-Hellman parameters \fBdh\fR are valid. The
value of \fB*codes\fR is updated with any problems found. If \fB*codes\fR is zero then
no problems were found, otherwise the following bits may be set:
.IP "\s-1DH_CHECK_P_NOT_PRIME\s0" 4
.IX Item "DH_CHECK_P_NOT_PRIME"
The parameter \fBp\fR is not prime.
.IP "\s-1DH_CHECK_P_NOT_SAFE_PRIME\s0" 4
.IX Item "DH_CHECK_P_NOT_SAFE_PRIME"
The parameter \fBp\fR is not a safe prime and no \fBq\fR value is present.
.IP "\s-1DH_UNABLE_TO_CHECK_GENERATOR\s0" 4
.IX Item "DH_UNABLE_TO_CHECK_GENERATOR"
The generator \fBg\fR cannot be checked for suitability.
.IP "\s-1DH_NOT_SUITABLE_GENERATOR\s0" 4
.IX Item "DH_NOT_SUITABLE_GENERATOR"
The generator \fBg\fR is not suitable.
.IP "\s-1DH_CHECK_Q_NOT_PRIME\s0" 4
.IX Item "DH_CHECK_Q_NOT_PRIME"
The parameter \fBq\fR is not prime.
.IP "\s-1DH_CHECK_INVALID_Q_VALUE\s0" 4
.IX Item "DH_CHECK_INVALID_Q_VALUE"
The parameter \fBq\fR is invalid.
.IP "\s-1DH_CHECK_INVALID_J_VALUE\s0" 4
.IX Item "DH_CHECK_INVALID_J_VALUE"
The parameter \fBj\fR is invalid.
.PP
\&\fIDH_check_ex()\fR, \fIDH_check_params()\fR and \fIDH_check_pub_key_ex()\fR are similar to
\&\fIDH_check()\fR and \fIDH_check_params()\fR respectively, but the error reasons are added
to the thread's error queue instead of provided as return values from the
function.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fIDH_generate_parameters_ex()\fR, \fIDH_check()\fR and \fIDH_check_params()\fR return 1
if the check could be performed, 0 otherwise.
.PP
\&\fIDH_generate_parameters()\fR returns a pointer to the \s-1DH\s0 structure or \s-1NULL\s0 if
the parameter generation fails.
.PP
\&\fIDH_check_ex()\fR, \fIDH_check_params()\fR and \fIDH_check_pub_key_ex()\fR return 1 if the
check is successful, 0 for failed.
.PP
The error codes can be obtained by \fIERR_get_error\fR\|(3).
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIDH_new\fR\|(3), \fIERR_get_error\fR\|(3), \fIRAND_bytes\fR\|(3),
\&\fIDH_free\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
\&\fIDH_generate_parameters()\fR was deprecated in OpenSSL 0.9.8; use
\&\fIDH_generate_parameters_ex()\fR instead.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2000\-2018 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the OpenSSL license (the \*(L"License\*(R").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file \s-1LICENSE\s0 in the source distribution or at
<https://www.openssl.org/source/license.html>.

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