1 /* $OpenBSD: dh_gen.c,v 1.17 2022/01/07 09:27:13 tb Exp $ */
2 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
3 * All rights reserved.
4 *
5 * This package is an SSL implementation written
6 * by Eric Young (eay@cryptsoft.com).
7 * The implementation was written so as to conform with Netscapes SSL.
8 *
9 * This library is free for commercial and non-commercial use as long as
10 * the following conditions are aheared to. The following conditions
11 * apply to all code found in this distribution, be it the RC4, RSA,
12 * lhash, DES, etc., code; not just the SSL code. The SSL documentation
13 * included with this distribution is covered by the same copyright terms
14 * except that the holder is Tim Hudson (tjh@cryptsoft.com).
15 *
16 * Copyright remains Eric Young's, and as such any Copyright notices in
17 * the code are not to be removed.
18 * If this package is used in a product, Eric Young should be given attribution
19 * as the author of the parts of the library used.
20 * This can be in the form of a textual message at program startup or
21 * in documentation (online or textual) provided with the package.
22 *
23 * Redistribution and use in source and binary forms, with or without
24 * modification, are permitted provided that the following conditions
25 * are met:
26 * 1. Redistributions of source code must retain the copyright
27 * notice, this list of conditions and the following disclaimer.
28 * 2. Redistributions in binary form must reproduce the above copyright
29 * notice, this list of conditions and the following disclaimer in the
30 * documentation and/or other materials provided with the distribution.
31 * 3. All advertising materials mentioning features or use of this software
32 * must display the following acknowledgement:
33 * "This product includes cryptographic software written by
34 * Eric Young (eay@cryptsoft.com)"
35 * The word 'cryptographic' can be left out if the rouines from the library
36 * being used are not cryptographic related :-).
37 * 4. If you include any Windows specific code (or a derivative thereof) from
38 * the apps directory (application code) you must include an acknowledgement:
39 * "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
40 *
41 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
42 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
43 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
44 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
45 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
46 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
47 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
48 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
49 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
50 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
51 * SUCH DAMAGE.
52 *
53 * The licence and distribution terms for any publically available version or
54 * derivative of this code cannot be changed. i.e. this code cannot simply be
55 * copied and put under another distribution licence
56 * [including the GNU Public Licence.]
57 */
58
59 /* NB: These functions have been upgraded - the previous prototypes are in
60 * dh_depr.c as wrappers to these ones.
61 * - Geoff
62 */
63
64 #include <stdio.h>
65
66 #include <openssl/bn.h>
67 #include <openssl/dh.h>
68 #include <openssl/err.h>
69
70 #include "dh_local.h"
71
72 static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
73 BN_GENCB *cb);
74
75 int
DH_generate_parameters_ex(DH * ret,int prime_len,int generator,BN_GENCB * cb)76 DH_generate_parameters_ex(DH *ret, int prime_len, int generator, BN_GENCB *cb)
77 {
78 if (ret->meth->generate_params)
79 return ret->meth->generate_params(ret, prime_len, generator, cb);
80 return dh_builtin_genparams(ret, prime_len, generator, cb);
81 }
82
83 /*
84 * We generate DH parameters as follows:
85 * find a prime q which is prime_len/2 bits long.
86 * p=(2*q)+1 or (p-1)/2 = q
87 * For this case, g is a generator if
88 * g^((p-1)/q) mod p != 1 for values of q which are the factors of p-1.
89 * Since the factors of p-1 are q and 2, we just need to check
90 * g^2 mod p != 1 and g^q mod p != 1.
91 *
92 * Having said all that,
93 * there is another special case method for the generators 2, 3 and 5.
94 * for 2, p mod 24 == 11
95 * for 3, p mod 12 == 5 <<<<< does not work for safe primes.
96 * for 5, p mod 10 == 3 or 7
97 *
98 * Thanks to Phil Karn <karn@qualcomm.com> for the pointers about the
99 * special generators and for answering some of my questions.
100 *
101 * I've implemented the second simple method :-).
102 * Since DH should be using a safe prime (both p and q are prime),
103 * this generator function can take a very very long time to run.
104 */
105 /* Actually there is no reason to insist that 'generator' be a generator.
106 * It's just as OK (and in some sense better) to use a generator of the
107 * order-q subgroup.
108 */
109 static int
dh_builtin_genparams(DH * ret,int prime_len,int generator,BN_GENCB * cb)110 dh_builtin_genparams(DH *ret, int prime_len, int generator, BN_GENCB *cb)
111 {
112 BIGNUM *t1, *t2;
113 int g, ok = -1;
114 BN_CTX *ctx = NULL;
115
116 ctx = BN_CTX_new();
117 if (ctx == NULL)
118 goto err;
119 BN_CTX_start(ctx);
120 if ((t1 = BN_CTX_get(ctx)) == NULL)
121 goto err;
122 if ((t2 = BN_CTX_get(ctx)) == NULL)
123 goto err;
124
125 /* Make sure 'ret' has the necessary elements */
126 if (!ret->p && ((ret->p = BN_new()) == NULL))
127 goto err;
128 if (!ret->g && ((ret->g = BN_new()) == NULL))
129 goto err;
130
131 if (generator <= 1) {
132 DHerror(DH_R_BAD_GENERATOR);
133 goto err;
134 }
135 if (generator == DH_GENERATOR_2) {
136 if (!BN_set_word(t1, 24))
137 goto err;
138 if (!BN_set_word(t2, 11))
139 goto err;
140 g = 2;
141 } else if (generator == DH_GENERATOR_5) {
142 if (!BN_set_word(t1, 10))
143 goto err;
144 if (!BN_set_word(t2, 3))
145 goto err;
146 /* BN_set_word(t3,7); just have to miss
147 * out on these ones :-( */
148 g = 5;
149 } else {
150 /*
151 * in the general case, don't worry if 'generator' is a
152 * generator or not: since we are using safe primes,
153 * it will generate either an order-q or an order-2q group,
154 * which both is OK
155 */
156 if (!BN_set_word(t1, 2))
157 goto err;
158 if (!BN_set_word(t2, 1))
159 goto err;
160 g = generator;
161 }
162
163 if (!BN_generate_prime_ex(ret->p, prime_len, 1, t1, t2, cb))
164 goto err;
165 if (!BN_GENCB_call(cb, 3, 0))
166 goto err;
167 if (!BN_set_word(ret->g, g))
168 goto err;
169 ok = 1;
170 err:
171 if (ok == -1) {
172 DHerror(ERR_R_BN_LIB);
173 ok = 0;
174 }
175
176 if (ctx != NULL) {
177 BN_CTX_end(ctx);
178 BN_CTX_free(ctx);
179 }
180 return ok;
181 }
182