1 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
4 * This package is an SSL implementation written
5 * by Eric Young (eay@cryptsoft.com).
6 * The implementation was written so as to conform with Netscapes SSL.
8 * This library is free for commercial and non-commercial use as long as
9 * the following conditions are aheared to. The following conditions
10 * apply to all code found in this distribution, be it the RC4, RSA,
11 * lhash, DES, etc., code; not just the SSL code. The SSL documentation
12 * included with this distribution is covered by the same copyright terms
13 * except that the holder is Tim Hudson (tjh@cryptsoft.com).
15 * Copyright remains Eric Young's, and as such any Copyright notices in
16 * the code are not to be removed.
17 * If this package is used in a product, Eric Young should be given attribution
18 * as the author of the parts of the library used.
19 * This can be in the form of a textual message at program startup or
20 * in documentation (online or textual) provided with the package.
22 * Redistribution and use in source and binary forms, with or without
23 * modification, are permitted provided that the following conditions
25 * 1. Redistributions of source code must retain the copyright
26 * notice, this list of conditions and the following disclaimer.
27 * 2. Redistributions in binary form must reproduce the above copyright
28 * notice, this list of conditions and the following disclaimer in the
29 * documentation and/or other materials provided with the distribution.
30 * 3. All advertising materials mentioning features or use of this software
31 * must display the following acknowledgement:
32 * "This product includes cryptographic software written by
33 * Eric Young (eay@cryptsoft.com)"
34 * The word 'cryptographic' can be left out if the rouines from the library
35 * being used are not cryptographic related :-).
36 * 4. If you include any Windows specific code (or a derivative thereof) from
37 * the apps directory (application code) you must include an acknowledgement:
38 * "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
40 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
41 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
42 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
43 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
44 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
45 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
46 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
47 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
48 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
49 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
52 * The licence and distribution terms for any publically available version or
53 * derivative of this code cannot be changed. i.e. this code cannot simply be
54 * copied and put under another distribution licence
55 * [including the GNU Public Licence.]
59 * NB: These functions have been upgraded - the previous prototypes are in
60 * dh_depr.c as wrappers to these ones. - Geoff
64 #include "internal/cryptlib.h"
65 #include <openssl/bn.h>
66 #include <openssl/dh.h>
68 static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
71 int DH_generate_parameters_ex(DH *ret, int prime_len, int generator,
74 if (ret->meth->generate_params)
75 return ret->meth->generate_params(ret, prime_len, generator, cb);
76 return dh_builtin_genparams(ret, prime_len, generator, cb);
80 * We generate DH parameters as follows
81 * find a prime q which is prime_len/2 bits long.
82 * p=(2*q)+1 or (p-1)/2 = q
83 * For this case, g is a generator if
84 * g^((p-1)/q) mod p != 1 for values of q which are the factors of p-1.
85 * Since the factors of p-1 are q and 2, we just need to check
86 * g^2 mod p != 1 and g^q mod p != 1.
88 * Having said all that,
89 * there is another special case method for the generators 2, 3 and 5.
90 * for 2, p mod 24 == 11
91 * for 3, p mod 12 == 5 <<<<< does not work for safe primes.
92 * for 5, p mod 10 == 3 or 7
94 * Thanks to Phil Karn <karn@qualcomm.com> for the pointers about the
95 * special generators and for answering some of my questions.
97 * I've implemented the second simple method :-).
98 * Since DH should be using a safe prime (both p and q are prime),
99 * this generator function can take a very very long time to run.
102 * Actually there is no reason to insist that 'generator' be a generator.
103 * It's just as OK (and in some sense better) to use a generator of the
106 static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
117 t1 = BN_CTX_get(ctx);
118 t2 = BN_CTX_get(ctx);
119 if (t1 == NULL || t2 == NULL)
122 /* Make sure 'ret' has the necessary elements */
123 if (!ret->p && ((ret->p = BN_new()) == NULL))
125 if (!ret->g && ((ret->g = BN_new()) == NULL))
128 if (generator <= 1) {
129 DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_BAD_GENERATOR);
132 if (generator == DH_GENERATOR_2) {
133 if (!BN_set_word(t1, 24))
135 if (!BN_set_word(t2, 11))
138 } else if (generator == DH_GENERATOR_5) {
139 if (!BN_set_word(t1, 10))
141 if (!BN_set_word(t2, 3))
144 * BN_set_word(t3,7); just have to miss out on these ones :-(
149 * in the general case, don't worry if 'generator' is a generator or
150 * not: since we are using safe primes, it will generate either an
151 * order-q or an order-2q group, which both is OK
153 if (!BN_set_word(t1, 2))
155 if (!BN_set_word(t2, 1))
160 if (!BN_generate_prime_ex(ret->p, prime_len, 1, t1, t2, cb))
162 if (!BN_GENCB_call(cb, 3, 0))
164 if (!BN_set_word(ret->g, g))
169 DHerr(DH_F_DH_BUILTIN_GENPARAMS, ERR_R_BN_LIB);