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