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+=pod
+
+=head1 NAME
+
+DH_generate_parameters_ex, DH_generate_parameters,
+DH_check, DH_check_params - generate and check Diffie-Hellman
+parameters
+
+=head1 SYNOPSIS
+
+ #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);
+
+Deprecated:
+
+ #if OPENSSL_API_COMPAT < 0x00908000L
+ DH *DH_generate_parameters(int prime_len, int generator,
+ void (*callback)(int, int, void *), void *cb_arg);
+ #endif
+
+=head1 DESCRIPTION
+
+DH_generate_parameters_ex() generates Diffie-Hellman parameters that can
+be shared among a group of users, and stores them in the provided B<DH>
+structure. The pseudo-random number generator must be
+seeded prior to calling DH_generate_parameters().
+
+B<prime_len> is the length in bits of the safe prime to be generated.
+B<generator> is a small number E<gt> 1, typically 2 or 5.
+
+A callback function may be used to provide feedback about the progress
+of the key generation. If B<cb> is not B<NULL>, it will be
+called as described in L<BN_generate_prime(3)> while a random prime
+number is generated, and when a prime has been found, B<BN_GENCB_call(cb, 3, 0)>
+is called. See L<BN_generate_prime(3)> for information on
+the BN_GENCB_call() function.
+
+DH_check_params() confirms that the B<p> and B<g> are likely enough to
+be valid.
+This is a lightweight check, if a more thorough check is needed, use
+DH_check().
+The value of B<*codes> is updated with any problems found.
+If B<*codes> is zero then no problems were found, otherwise the
+following bits may be set:
+
+=over 4
+
+=item DH_CHECK_P_NOT_PRIME
+
+The parameter B<p> has been determined to not being an odd prime.
+Note that the lack of this bit doesn't guarantee that B<p> is a
+prime.
+
+=item DH_NOT_SUITABLE_GENERATOR
+
+The generator B<g> is not suitable.
+Note that the lack of this bit doesn't guarantee that B<g> is
+suitable, unless B<p> is known to be a strong prime.
+
+=back
+
+DH_check() confirms that the Diffie-Hellman parameters B<dh> are valid. The
+value of B<*codes> is updated with any problems found. If B<*codes> is zero then
+no problems were found, otherwise the following bits may be set:
+
+=over 4
+
+=item DH_CHECK_P_NOT_PRIME
+
+The parameter B<p> is not prime.
+
+=item DH_CHECK_P_NOT_SAFE_PRIME
+
+The parameter B<p> is not a safe prime and no B<q> value is present.
+
+=item DH_UNABLE_TO_CHECK_GENERATOR
+
+The generator B<g> cannot be checked for suitability.
+
+=item DH_NOT_SUITABLE_GENERATOR
+
+The generator B<g> is not suitable.
+
+=item DH_CHECK_Q_NOT_PRIME
+
+The parameter B<q> is not prime.
+
+=item DH_CHECK_INVALID_Q_VALUE
+
+The parameter B<q> is invalid.
+
+=item DH_CHECK_INVALID_J_VALUE
+
+The parameter B<j> is invalid.
+
+=back
+
+=head1 RETURN VALUES
+
+DH_generate_parameters_ex(), DH_check() and DH_check_params() return 1
+if the check could be performed, 0 otherwise.
+
+DH_generate_parameters() (deprecated) returns a pointer to the DH structure, or
+NULL if the parameter generation fails.
+
+The error codes can be obtained by L<ERR_get_error(3)>.
+
+=head1 NOTES
+
+DH_generate_parameters_ex() and DH_generate_parameters() may run for several
+hours before finding a suitable prime.
+
+The parameters generated by DH_generate_parameters_ex() and DH_generate_parameters()
+are not to be used in signature schemes.
+
+=head1 SEE ALSO
+
+L<DH_new(3)>, L<ERR_get_error(3)>, L<RAND_bytes(3)>,
+L<DH_free(3)>
+
+=head1 COPYRIGHT
+
+Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.
+
+Licensed under the OpenSSL license (the "License"). You may not use
+this file except in compliance with the License. You can obtain a copy
+in the file LICENSE in the source distribution or at
+L<https://www.openssl.org/source/license.html>.
+
+=cut