1/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
2 * All rights reserved.
3 *
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.
7 *
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).
14 *
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.
21 *
22 * Redistribution and use in source and binary forms, with or without
23 * modification, are permitted provided that the following conditions
24 * are met:
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)"
39 *
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
50 * SUCH DAMAGE.
51 *
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.] */
56
57#include <openssl/dh.h>
58
59#include <openssl/bn.h>
60#include <openssl/err.h>
61
62#include "internal.h"
63
64#define OPENSSL_DH_MAX_MODULUS_BITS 10000
65
66static int generate_parameters(DH *ret, int prime_bits, int generator, BN_GENCB *cb) {
67  /* We generate DH parameters as follows
68   * find a prime q which is prime_bits/2 bits long.
69   * p=(2*q)+1 or (p-1)/2 = q
70   * For this case, g is a generator if
71   * g^((p-1)/q) mod p != 1 for values of q which are the factors of p-1.
72   * Since the factors of p-1 are q and 2, we just need to check
73   * g^2 mod p != 1 and g^q mod p != 1.
74   *
75   * Having said all that,
76   * there is another special case method for the generators 2, 3 and 5.
77   * for 2, p mod 24 == 11
78   * for 3, p mod 12 == 5  <<<<< does not work for safe primes.
79   * for 5, p mod 10 == 3 or 7
80   *
81   * Thanks to Phil Karn <karn@qualcomm.com> for the pointers about the
82   * special generators and for answering some of my questions.
83   *
84   * I've implemented the second simple method :-).
85   * Since DH should be using a safe prime (both p and q are prime),
86   * this generator function can take a very very long time to run.
87   */
88
89  /* Actually there is no reason to insist that 'generator' be a generator.
90   * It's just as OK (and in some sense better) to use a generator of the
91   * order-q subgroup.
92   */
93
94  BIGNUM *t1, *t2;
95  int g, ok = 0;
96  BN_CTX *ctx = NULL;
97
98  ctx = BN_CTX_new();
99  if (ctx == NULL) {
100    goto err;
101  }
102  BN_CTX_start(ctx);
103  t1 = BN_CTX_get(ctx);
104  t2 = BN_CTX_get(ctx);
105  if (t1 == NULL || t2 == NULL) {
106    goto err;
107  }
108
109  /* Make sure 'ret' has the necessary elements */
110  if (!ret->p && ((ret->p = BN_new()) == NULL)) {
111    goto err;
112  }
113  if (!ret->g && ((ret->g = BN_new()) == NULL)) {
114    goto err;
115  }
116
117  if (generator <= 1) {
118    OPENSSL_PUT_ERROR(DH, generate_parameters, DH_R_BAD_GENERATOR);
119    goto err;
120  }
121  if (generator == DH_GENERATOR_2) {
122    if (!BN_set_word(t1, 24)) {
123      goto err;
124    }
125    if (!BN_set_word(t2, 11)) {
126      goto err;
127    }
128    g = 2;
129  } else if (generator == DH_GENERATOR_5) {
130    if (!BN_set_word(t1, 10)) {
131      goto err;
132    }
133    if (!BN_set_word(t2, 3)) {
134      goto err;
135    }
136    /* BN_set_word(t3,7); just have to miss
137     * out on these ones :-( */
138    g = 5;
139  } else {
140    /* in the general case, don't worry if 'generator' is a
141     * generator or not: since we are using safe primes,
142     * it will generate either an order-q or an order-2q group,
143     * which both is OK */
144    if (!BN_set_word(t1, 2)) {
145      goto err;
146    }
147    if (!BN_set_word(t2, 1)) {
148      goto err;
149    }
150    g = generator;
151  }
152
153  if (!BN_generate_prime_ex(ret->p, prime_bits, 1, t1, t2, cb)) {
154    goto err;
155  }
156  if (!BN_GENCB_call(cb, 3, 0)) {
157    goto err;
158  }
159  if (!BN_set_word(ret->g, g)) {
160    goto err;
161  }
162  ok = 1;
163
164err:
165  if (!ok) {
166    OPENSSL_PUT_ERROR(DH, generate_parameters, ERR_R_BN_LIB);
167  }
168
169  if (ctx != NULL) {
170    BN_CTX_end(ctx);
171    BN_CTX_free(ctx);
172  }
173  return ok;
174}
175
176static int generate_key(DH *dh) {
177  int ok = 0;
178  int generate_new_key = 0;
179  unsigned l;
180  BN_CTX *ctx;
181  BN_MONT_CTX *mont = NULL;
182  BIGNUM *pub_key = NULL, *priv_key = NULL;
183  BIGNUM local_priv;
184
185  ctx = BN_CTX_new();
186  if (ctx == NULL) {
187    goto err;
188  }
189
190  if (dh->priv_key == NULL) {
191    priv_key = BN_new();
192    if (priv_key == NULL) {
193      goto err;
194    }
195    generate_new_key = 1;
196  } else {
197    priv_key = dh->priv_key;
198  }
199
200  if (dh->pub_key == NULL) {
201    pub_key = BN_new();
202    if (pub_key == NULL) {
203      goto err;
204    }
205  } else {
206    pub_key = dh->pub_key;
207  }
208
209  mont =
210      BN_MONT_CTX_set_locked(&dh->method_mont_p, CRYPTO_LOCK_DH, dh->p, ctx);
211  if (!mont) {
212    goto err;
213  }
214
215  if (generate_new_key) {
216    if (dh->q) {
217      do {
218        if (!BN_rand_range(priv_key, dh->q)) {
219          goto err;
220        }
221      } while (BN_is_zero(priv_key) || BN_is_one(priv_key));
222    } else {
223      /* secret exponent length */
224      l = dh->priv_length ? dh->priv_length : BN_num_bits(dh->p) - 1;
225      if (!BN_rand(priv_key, l, 0, 0)) {
226        goto err;
227      }
228    }
229  }
230
231  BN_with_flags(&local_priv, priv_key, BN_FLG_CONSTTIME);
232  if (!BN_mod_exp_mont(pub_key, dh->g, &local_priv, dh->p, ctx, mont)) {
233    goto err;
234  }
235
236  dh->pub_key = pub_key;
237  dh->priv_key = priv_key;
238  ok = 1;
239
240err:
241  if (ok != 1) {
242    OPENSSL_PUT_ERROR(DH, generate_key, ERR_R_BN_LIB);
243  }
244
245  if (pub_key != NULL && dh->pub_key == NULL) {
246    BN_free(pub_key);
247  }
248  if (priv_key != NULL && dh->priv_key == NULL) {
249    BN_free(priv_key);
250  }
251  BN_CTX_free(ctx);
252  return ok;
253}
254
255static int compute_key(DH *dh, unsigned char *out, const BIGNUM *pub_key) {
256  BN_CTX *ctx = NULL;
257  BN_MONT_CTX *mont = NULL;
258  BIGNUM *shared_key;
259  int ret = -1;
260  int check_result;
261  BIGNUM local_priv;
262
263  if (BN_num_bits(dh->p) > OPENSSL_DH_MAX_MODULUS_BITS) {
264    OPENSSL_PUT_ERROR(DH, compute_key, DH_R_MODULUS_TOO_LARGE);
265    goto err;
266  }
267
268  ctx = BN_CTX_new();
269  if (ctx == NULL) {
270    goto err;
271  }
272  BN_CTX_start(ctx);
273  shared_key = BN_CTX_get(ctx);
274  if (shared_key == NULL) {
275    goto err;
276  }
277
278  if (dh->priv_key == NULL) {
279    OPENSSL_PUT_ERROR(DH, compute_key, DH_R_NO_PRIVATE_VALUE);
280    goto err;
281  }
282
283  mont =
284      BN_MONT_CTX_set_locked(&dh->method_mont_p, CRYPTO_LOCK_DH, dh->p, ctx);
285  if (!mont) {
286    goto err;
287  }
288
289  if (!DH_check_pub_key(dh, pub_key, &check_result) || check_result) {
290    OPENSSL_PUT_ERROR(DH, compute_key, DH_R_INVALID_PUBKEY);
291    goto err;
292  }
293
294  BN_with_flags(&local_priv, dh->priv_key, BN_FLG_CONSTTIME);
295  if (!BN_mod_exp_mont(shared_key, pub_key, &local_priv, dh->p, ctx,
296                       mont)) {
297    OPENSSL_PUT_ERROR(DH, compute_key, ERR_R_BN_LIB);
298    goto err;
299  }
300
301  ret = BN_bn2bin(shared_key, out);
302
303err:
304  if (ctx != NULL) {
305    BN_CTX_end(ctx);
306    BN_CTX_free(ctx);
307  }
308
309  return ret;
310}
311
312const struct dh_method DH_default_method = {
313  {
314    0 /* references */,
315    1 /* is_static */,
316  },
317  NULL /* app_data */,
318  NULL /* init */,
319  NULL /* finish */,
320  generate_parameters,
321  generate_key,
322  compute_key,
323};
324