1 /* crypto/dh/dh_gen.c */
2 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
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.
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).
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.
23 * Redistribution and use in source and binary forms, with or without
24 * modification, are permitted provided that the following conditions
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)"
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
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.]
59 /* NB: These functions have been upgraded - the previous prototypes are in
60 * dh_depr.c as wrappers to these ones.
66 #include <openssl/bn.h>
67 #include <openssl/dh.h>
69 static int dh_builtin_genparams(DH *ret, int prime_len, int generator, BN_GENCB *cb);
71 EXPORT_C int DH_generate_parameters_ex(DH *ret, int prime_len, int generator, BN_GENCB *cb)
73 if(ret->meth->generate_params)
74 return ret->meth->generate_params(ret, prime_len, generator, cb);
75 return dh_builtin_genparams(ret, prime_len, generator, cb);
78 /* We generate DH parameters as follows
79 * find a prime q which is prime_len/2 bits long.
80 * p=(2*q)+1 or (p-1)/2 = q
81 * For this case, g is a generator if
82 * g^((p-1)/q) mod p != 1 for values of q which are the factors of p-1.
83 * Since the factors of p-1 are q and 2, we just need to check
84 * g^2 mod p != 1 and g^q mod p != 1.
86 * Having said all that,
87 * there is another special case method for the generators 2, 3 and 5.
88 * for 2, p mod 24 == 11
89 * for 3, p mod 12 == 5 <<<<< does not work for safe primes.
90 * for 5, p mod 10 == 3 or 7
92 * Thanks to Phil Karn <karn@qualcomm.com> for the pointers about the
93 * special generators and for answering some of my questions.
95 * I've implemented the second simple method :-).
96 * Since DH should be using a safe prime (both p and q are prime),
97 * this generator function can take a very very long time to run.
99 /* Actually there is no reason to insist that 'generator' be a generator.
100 * It's just as OK (and in some sense better) to use a generator of the
103 static int dh_builtin_genparams(DH *ret, int prime_len, int generator, BN_GENCB *cb)
110 if (ctx == NULL) goto err;
112 t1 = BN_CTX_get(ctx);
113 t2 = BN_CTX_get(ctx);
114 if (t1 == NULL || t2 == NULL) goto err;
116 /* Make sure 'ret' has the necessary elements */
117 if(!ret->p && ((ret->p = BN_new()) == NULL)) goto err;
118 if(!ret->g && ((ret->g = BN_new()) == NULL)) goto err;
122 DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_BAD_GENERATOR);
125 if (generator == DH_GENERATOR_2)
127 if (!BN_set_word(t1,24)) goto err;
128 if (!BN_set_word(t2,11)) goto err;
131 #if 0 /* does not work for safe primes */
132 else if (generator == DH_GENERATOR_3)
134 if (!BN_set_word(t1,12)) goto err;
135 if (!BN_set_word(t2,5)) goto err;
139 else if (generator == DH_GENERATOR_5)
141 if (!BN_set_word(t1,10)) goto err;
142 if (!BN_set_word(t2,3)) goto err;
143 /* BN_set_word(t3,7); just have to miss
144 * out on these ones :-( */
149 /* in the general case, don't worry if 'generator' is a
150 * generator or not: since we are using safe primes,
151 * it will generate either an order-q or an order-2q group,
152 * which both is OK */
153 if (!BN_set_word(t1,2)) goto err;
154 if (!BN_set_word(t2,1)) goto err;
158 if(!BN_generate_prime_ex(ret->p,prime_len,1,t1,t2,cb)) goto err;
159 if(!BN_GENCB_call(cb, 3, 0)) goto err;
160 if (!BN_set_word(ret->g,g)) goto err;
165 DHerr(DH_F_DH_BUILTIN_GENPARAMS,ERR_R_BN_LIB);