1=pod
2
3=head1 NAME
4
5DH_generate_parameters_ex, DH_generate_parameters,
6DH_check, DH_check_params,
7DH_check_ex, DH_check_params_ex, DH_check_pub_key_ex
8- generate and check Diffie-Hellman
9parameters
10
11=head1 SYNOPSIS
12
13 #include <openssl/dh.h>
14
15 int DH_generate_parameters_ex(DH *dh, int prime_len, int generator, BN_GENCB *cb);
16
17 int DH_check(DH *dh, int *codes);
18 int DH_check_params(DH *dh, int *codes);
19
20 int DH_check_ex(const DH *dh);
21 int DH_check_params_ex(const DH *dh);
22 int DH_check_pub_key_ex(const DH *dh, const BIGNUM *pub_key);
23
24Deprecated:
25
26 #if OPENSSL_API_COMPAT < 0x00908000L
27 DH *DH_generate_parameters(int prime_len, int generator,
28                            void (*callback)(int, int, void *), void *cb_arg);
29 #endif
30
31=head1 DESCRIPTION
32
33DH_generate_parameters_ex() generates Diffie-Hellman parameters that can
34be shared among a group of users, and stores them in the provided B<DH>
35structure. The pseudo-random number generator must be
36seeded before calling it.
37The parameters generated by DH_generate_parameters_ex() should not be used in
38signature schemes.
39
40B<prime_len> is the length in bits of the safe prime to be generated.
41B<generator> is a small number E<gt> 1, typically 2 or 5.
42
43A callback function may be used to provide feedback about the progress
44of the key generation. If B<cb> is not B<NULL>, it will be
45called as described in L<BN_generate_prime(3)> while a random prime
46number is generated, and when a prime has been found, B<BN_GENCB_call(cb, 3, 0)>
47is called. See L<BN_generate_prime_ex(3)> for information on
48the BN_GENCB_call() function.
49
50DH_generate_parameters() is similar to DH_generate_prime_ex() but
51expects an old-style callback function; see
52L<BN_generate_prime(3)> for information on the old-style callback.
53
54DH_check_params() confirms that the B<p> and B<g> are likely enough to
55be valid.
56This is a lightweight check, if a more thorough check is needed, use
57DH_check().
58The value of B<*codes> is updated with any problems found.
59If B<*codes> is zero then no problems were found, otherwise the
60following bits may be set:
61
62=over 4
63
64=item DH_CHECK_P_NOT_PRIME
65
66The parameter B<p> has been determined to not being an odd prime.
67Note that the lack of this bit doesn't guarantee that B<p> is a
68prime.
69
70=item DH_NOT_SUITABLE_GENERATOR
71
72The generator B<g> is not suitable.
73Note that the lack of this bit doesn't guarantee that B<g> is
74suitable, unless B<p> is known to be a strong prime.
75
76=back
77
78DH_check() confirms that the Diffie-Hellman parameters B<dh> are valid. The
79value of B<*codes> is updated with any problems found. If B<*codes> is zero then
80no problems were found, otherwise the following bits may be set:
81
82=over 4
83
84=item DH_CHECK_P_NOT_PRIME
85
86The parameter B<p> is not prime.
87
88=item DH_CHECK_P_NOT_SAFE_PRIME
89
90The parameter B<p> is not a safe prime and no B<q> value is present.
91
92=item DH_UNABLE_TO_CHECK_GENERATOR
93
94The generator B<g> cannot be checked for suitability.
95
96=item DH_NOT_SUITABLE_GENERATOR
97
98The generator B<g> is not suitable.
99
100=item DH_CHECK_Q_NOT_PRIME
101
102The parameter B<q> is not prime.
103
104=item DH_CHECK_INVALID_Q_VALUE
105
106The parameter B<q> is invalid.
107
108=item DH_CHECK_INVALID_J_VALUE
109
110The parameter B<j> is invalid.
111
112=back
113
114DH_check_ex(), DH_check_params() and DH_check_pub_key_ex() are similar to
115DH_check() and DH_check_params() respectively, but the error reasons are added
116to the thread's error queue instead of provided as return values from the
117function.
118
119=head1 RETURN VALUES
120
121DH_generate_parameters_ex(), DH_check() and DH_check_params() return 1
122if the check could be performed, 0 otherwise.
123
124DH_generate_parameters() returns a pointer to the DH structure or NULL if
125the parameter generation fails.
126
127DH_check_ex(), DH_check_params() and DH_check_pub_key_ex() return 1 if the
128check is successful, 0 for failed.
129
130The error codes can be obtained by L<ERR_get_error(3)>.
131
132=head1 SEE ALSO
133
134L<DH_new(3)>, L<ERR_get_error(3)>, L<RAND_bytes(3)>,
135L<DH_free(3)>
136
137=head1 HISTORY
138
139DH_generate_parameters() was deprecated in OpenSSL 0.9.8; use
140DH_generate_parameters_ex() instead.
141
142=head1 COPYRIGHT
143
144Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.
145
146Licensed under the OpenSSL license (the "License").  You may not use
147this file except in compliance with the License.  You can obtain a copy
148in the file LICENSE in the source distribution or at
149L<https://www.openssl.org/source/license.html>.
150
151=cut
152