Line data Source code
1 : /* crypto/dh/dh_gen.c */
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 : /*
60 : * NB: These functions have been upgraded - the previous prototypes are in
61 : * dh_depr.c as wrappers to these ones. - Geoff
62 : */
63 :
64 : #include <stdio.h>
65 : #include "cryptlib.h"
66 : #include <openssl/bn.h>
67 : #include <openssl/dh.h>
68 :
69 : #ifdef OPENSSL_FIPS
70 : # include <openssl/fips.h>
71 : #endif
72 :
73 : static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
74 : BN_GENCB *cb);
75 :
76 0 : int DH_generate_parameters_ex(DH *ret, int prime_len, int generator,
77 : BN_GENCB *cb)
78 : {
79 : #ifdef OPENSSL_FIPS
80 : if (FIPS_mode() && !(ret->meth->flags & DH_FLAG_FIPS_METHOD)
81 : && !(ret->flags & DH_FLAG_NON_FIPS_ALLOW)) {
82 : DHerr(DH_F_DH_GENERATE_PARAMETERS_EX, DH_R_NON_FIPS_METHOD);
83 : return 0;
84 : }
85 : #endif
86 0 : if (ret->meth->generate_params)
87 0 : return ret->meth->generate_params(ret, prime_len, generator, cb);
88 : #ifdef OPENSSL_FIPS
89 : if (FIPS_mode())
90 : return FIPS_dh_generate_parameters_ex(ret, prime_len, generator, cb);
91 : #endif
92 0 : return dh_builtin_genparams(ret, prime_len, generator, cb);
93 : }
94 :
95 : /*-
96 : * We generate DH parameters as follows
97 : * find a prime q which is prime_len/2 bits long.
98 : * p=(2*q)+1 or (p-1)/2 = q
99 : * For this case, g is a generator if
100 : * g^((p-1)/q) mod p != 1 for values of q which are the factors of p-1.
101 : * Since the factors of p-1 are q and 2, we just need to check
102 : * g^2 mod p != 1 and g^q mod p != 1.
103 : *
104 : * Having said all that,
105 : * there is another special case method for the generators 2, 3 and 5.
106 : * for 2, p mod 24 == 11
107 : * for 3, p mod 12 == 5 <<<<< does not work for safe primes.
108 : * for 5, p mod 10 == 3 or 7
109 : *
110 : * Thanks to Phil Karn <karn@qualcomm.com> for the pointers about the
111 : * special generators and for answering some of my questions.
112 : *
113 : * I've implemented the second simple method :-).
114 : * Since DH should be using a safe prime (both p and q are prime),
115 : * this generator function can take a very very long time to run.
116 : */
117 : /*
118 : * Actually there is no reason to insist that 'generator' be a generator.
119 : * It's just as OK (and in some sense better) to use a generator of the
120 : * order-q subgroup.
121 : */
122 0 : static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
123 : BN_GENCB *cb)
124 : {
125 : BIGNUM *t1, *t2;
126 : int g, ok = -1;
127 : BN_CTX *ctx = NULL;
128 :
129 0 : ctx = BN_CTX_new();
130 0 : if (ctx == NULL)
131 : goto err;
132 0 : BN_CTX_start(ctx);
133 0 : t1 = BN_CTX_get(ctx);
134 0 : t2 = BN_CTX_get(ctx);
135 0 : if (t1 == NULL || t2 == NULL)
136 : goto err;
137 :
138 : /* Make sure 'ret' has the necessary elements */
139 0 : if (!ret->p && ((ret->p = BN_new()) == NULL))
140 : goto err;
141 0 : if (!ret->g && ((ret->g = BN_new()) == NULL))
142 : goto err;
143 :
144 0 : if (generator <= 1) {
145 0 : DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_BAD_GENERATOR);
146 : goto err;
147 : }
148 0 : if (generator == DH_GENERATOR_2) {
149 0 : if (!BN_set_word(t1, 24))
150 : goto err;
151 0 : if (!BN_set_word(t2, 11))
152 : goto err;
153 : g = 2;
154 : }
155 : #if 0 /* does not work for safe primes */
156 : else if (generator == DH_GENERATOR_3) {
157 : if (!BN_set_word(t1, 12))
158 : goto err;
159 : if (!BN_set_word(t2, 5))
160 : goto err;
161 : g = 3;
162 : }
163 : #endif
164 0 : else if (generator == DH_GENERATOR_5) {
165 0 : if (!BN_set_word(t1, 10))
166 : goto err;
167 0 : if (!BN_set_word(t2, 3))
168 : goto err;
169 : /*
170 : * BN_set_word(t3,7); just have to miss out on these ones :-(
171 : */
172 : g = 5;
173 : } else {
174 : /*
175 : * in the general case, don't worry if 'generator' is a generator or
176 : * not: since we are using safe primes, it will generate either an
177 : * order-q or an order-2q group, which both is OK
178 : */
179 0 : if (!BN_set_word(t1, 2))
180 : goto err;
181 0 : if (!BN_set_word(t2, 1))
182 : goto err;
183 : g = generator;
184 : }
185 :
186 0 : if (!BN_generate_prime_ex(ret->p, prime_len, 1, t1, t2, cb))
187 : goto err;
188 0 : if (!BN_GENCB_call(cb, 3, 0))
189 : goto err;
190 0 : if (!BN_set_word(ret->g, g))
191 : goto err;
192 : ok = 1;
193 : err:
194 0 : if (ok == -1) {
195 0 : DHerr(DH_F_DH_BUILTIN_GENPARAMS, ERR_R_BN_LIB);
196 : ok = 0;
197 : }
198 :
199 0 : if (ctx != NULL) {
200 0 : BN_CTX_end(ctx);
201 0 : BN_CTX_free(ctx);
202 : }
203 0 : return ok;
204 : }
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