1/*
2 * Copyright 1995-2018 The OpenSSL Project Authors. All Rights Reserved.
3 *
4 * Licensed under the Apache License 2.0 (the "License"). You may not use
5 * this file except in compliance with the License. You can obtain a copy
6 * in the file LICENSE in the source distribution or at
7 * https://www.openssl.org/source/license.html
8 */
9
10#include <stdio.h>
11#include <time.h>
12#include "internal/cryptlib.h"
13#include "crypto/rand.h"
14#include "bn_local.h"
15#include <openssl/rand.h>
16#include <openssl/sha.h>
17#include <openssl/evp.h>
18
19typedef enum bnrand_flag_e {
20 NORMAL, TESTING, PRIVATE
21} BNRAND_FLAG;
22
23static int bnrand(BNRAND_FLAG flag, BIGNUM *rnd, int bits, int top, int bottom,
24 BN_CTX *ctx)
25{
26 unsigned char *buf = NULL;
27 int b, ret = 0, bit, bytes, mask;
28 OPENSSL_CTX *libctx = bn_get_lib_ctx(ctx);
29
30 if (bits == 0) {
31 if (top != BN_RAND_TOP_ANY || bottom != BN_RAND_BOTTOM_ANY)
32 goto toosmall;
33 BN_zero(rnd);
34 return 1;
35 }
36 if (bits < 0 || (bits == 1 && top > 0))
37 goto toosmall;
38
39 bytes = (bits + 7) / 8;
40 bit = (bits - 1) % 8;
41 mask = 0xff << (bit + 1);
42
43 buf = OPENSSL_malloc(bytes);
44 if (buf == NULL) {
45 BNerr(BN_F_BNRAND, ERR_R_MALLOC_FAILURE);
46 goto err;
47 }
48
49 /* make a random number and set the top and bottom bits */
50 b = flag == NORMAL ? rand_bytes_ex(libctx, buf, bytes)
51 : rand_priv_bytes_ex(libctx, buf, bytes);
52 if (b <= 0)
53 goto err;
54
55 if (flag == TESTING) {
56 /*
57 * generate patterns that are more likely to trigger BN library bugs
58 */
59 int i;
60 unsigned char c;
61
62 for (i = 0; i < bytes; i++) {
63 if (rand_bytes_ex(libctx, &c, 1) <= 0)
64 goto err;
65 if (c >= 128 && i > 0)
66 buf[i] = buf[i - 1];
67 else if (c < 42)
68 buf[i] = 0;
69 else if (c < 84)
70 buf[i] = 255;
71 }
72 }
73
74 if (top >= 0) {
75 if (top) {
76 if (bit == 0) {
77 buf[0] = 1;
78 buf[1] |= 0x80;
79 } else {
80 buf[0] |= (3 << (bit - 1));
81 }
82 } else {
83 buf[0] |= (1 << bit);
84 }
85 }
86 buf[0] &= ~mask;
87 if (bottom) /* set bottom bit if requested */
88 buf[bytes - 1] |= 1;
89 if (!BN_bin2bn(buf, bytes, rnd))
90 goto err;
91 ret = 1;
92 err:
93 OPENSSL_clear_free(buf, bytes);
94 bn_check_top(rnd);
95 return ret;
96
97toosmall:
98 BNerr(BN_F_BNRAND, BN_R_BITS_TOO_SMALL);
99 return 0;
100}
101
102int BN_rand_ex(BIGNUM *rnd, int bits, int top, int bottom, BN_CTX *ctx)
103{
104 return bnrand(NORMAL, rnd, bits, top, bottom, ctx);
105}
106#ifndef FIPS_MODE
107int BN_rand(BIGNUM *rnd, int bits, int top, int bottom)
108{
109 return bnrand(NORMAL, rnd, bits, top, bottom, NULL);
110}
111
112int BN_bntest_rand(BIGNUM *rnd, int bits, int top, int bottom)
113{
114 return bnrand(TESTING, rnd, bits, top, bottom, NULL);
115}
116#endif
117
118int BN_priv_rand_ex(BIGNUM *rnd, int bits, int top, int bottom, BN_CTX *ctx)
119{
120 return bnrand(PRIVATE, rnd, bits, top, bottom, ctx);
121}
122
123#ifndef FIPS_MODE
124int BN_priv_rand(BIGNUM *rnd, int bits, int top, int bottom)
125{
126 return bnrand(PRIVATE, rnd, bits, top, bottom, NULL);
127}
128#endif
129
130/* random number r: 0 <= r < range */
131static int bnrand_range(BNRAND_FLAG flag, BIGNUM *r, const BIGNUM *range,
132 BN_CTX *ctx)
133{
134 int n;
135 int count = 100;
136
137 if (range->neg || BN_is_zero(range)) {
138 BNerr(BN_F_BNRAND_RANGE, BN_R_INVALID_RANGE);
139 return 0;
140 }
141
142 n = BN_num_bits(range); /* n > 0 */
143
144 /* BN_is_bit_set(range, n - 1) always holds */
145
146 if (n == 1)
147 BN_zero(r);
148 else if (!BN_is_bit_set(range, n - 2) && !BN_is_bit_set(range, n - 3)) {
149 /*
150 * range = 100..._2, so 3*range (= 11..._2) is exactly one bit longer
151 * than range
152 */
153 do {
154 if (!bnrand(flag, r, n + 1, BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY,
155 ctx))
156 return 0;
157
158 /*
159 * If r < 3*range, use r := r MOD range (which is either r, r -
160 * range, or r - 2*range). Otherwise, iterate once more. Since
161 * 3*range = 11..._2, each iteration succeeds with probability >=
162 * .75.
163 */
164 if (BN_cmp(r, range) >= 0) {
165 if (!BN_sub(r, r, range))
166 return 0;
167 if (BN_cmp(r, range) >= 0)
168 if (!BN_sub(r, r, range))
169 return 0;
170 }
171
172 if (!--count) {
173 BNerr(BN_F_BNRAND_RANGE, BN_R_TOO_MANY_ITERATIONS);
174 return 0;
175 }
176
177 }
178 while (BN_cmp(r, range) >= 0);
179 } else {
180 do {
181 /* range = 11..._2 or range = 101..._2 */
182 if (!bnrand(flag, r, n, BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY, ctx))
183 return 0;
184
185 if (!--count) {
186 BNerr(BN_F_BNRAND_RANGE, BN_R_TOO_MANY_ITERATIONS);
187 return 0;
188 }
189 }
190 while (BN_cmp(r, range) >= 0);
191 }
192
193 bn_check_top(r);
194 return 1;
195}
196
197int BN_rand_range_ex(BIGNUM *r, const BIGNUM *range, BN_CTX *ctx)
198{
199 return bnrand_range(NORMAL, r, range, ctx);
200}
201
202#ifndef FIPS_MODE
203int BN_rand_range(BIGNUM *r, const BIGNUM *range)
204{
205 return bnrand_range(NORMAL, r, range, NULL);
206}
207#endif
208
209int BN_priv_rand_range_ex(BIGNUM *r, const BIGNUM *range, BN_CTX *ctx)
210{
211 return bnrand_range(PRIVATE, r, range, ctx);
212}
213
214#ifndef FIPS_MODE
215int BN_priv_rand_range(BIGNUM *r, const BIGNUM *range)
216{
217 return bnrand_range(PRIVATE, r, range, NULL);
218}
219
220int BN_pseudo_rand(BIGNUM *rnd, int bits, int top, int bottom)
221{
222 return BN_rand(rnd, bits, top, bottom);
223}
224
225int BN_pseudo_rand_range(BIGNUM *r, const BIGNUM *range)
226{
227 return BN_rand_range(r, range);
228}
229#endif
230
231/*
232 * BN_generate_dsa_nonce generates a random number 0 <= out < range. Unlike
233 * BN_rand_range, it also includes the contents of |priv| and |message| in
234 * the generation so that an RNG failure isn't fatal as long as |priv|
235 * remains secret. This is intended for use in DSA and ECDSA where an RNG
236 * weakness leads directly to private key exposure unless this function is
237 * used.
238 */
239int BN_generate_dsa_nonce(BIGNUM *out, const BIGNUM *range,
240 const BIGNUM *priv, const unsigned char *message,
241 size_t message_len, BN_CTX *ctx)
242{
243 EVP_MD_CTX *mdctx = EVP_MD_CTX_new();
244 /*
245 * We use 512 bits of random data per iteration to ensure that we have at
246 * least |range| bits of randomness.
247 */
248 unsigned char random_bytes[64];
249 unsigned char digest[SHA512_DIGEST_LENGTH];
250 unsigned done, todo;
251 /* We generate |range|+8 bytes of random output. */
252 const unsigned num_k_bytes = BN_num_bytes(range) + 8;
253 unsigned char private_bytes[96];
254 unsigned char *k_bytes = NULL;
255 int ret = 0;
256 EVP_MD *md = NULL;
257 OPENSSL_CTX *libctx = bn_get_lib_ctx(ctx);
258
259 if (mdctx == NULL)
260 goto err;
261
262 k_bytes = OPENSSL_malloc(num_k_bytes);
263 if (k_bytes == NULL)
264 goto err;
265
266 /* We copy |priv| into a local buffer to avoid exposing its length. */
267 if (BN_bn2binpad(priv, private_bytes, sizeof(private_bytes)) < 0) {
268 /*
269 * No reasonable DSA or ECDSA key should have a private key this
270 * large and we don't handle this case in order to avoid leaking the
271 * length of the private key.
272 */
273 BNerr(BN_F_BN_GENERATE_DSA_NONCE, BN_R_PRIVATE_KEY_TOO_LARGE);
274 goto err;
275 }
276
277 md = EVP_MD_fetch(libctx, "SHA512", NULL);
278 if (md == NULL) {
279 BNerr(BN_F_BN_GENERATE_DSA_NONCE, BN_R_NO_SUITABLE_DIGEST);
280 goto err;
281 }
282 for (done = 0; done < num_k_bytes;) {
283 if (!rand_priv_bytes_ex(libctx, random_bytes, sizeof(random_bytes)))
284 goto err;
285
286 if (!EVP_DigestInit_ex(mdctx, md, NULL)
287 || !EVP_DigestUpdate(mdctx, &done, sizeof(done))
288 || !EVP_DigestUpdate(mdctx, private_bytes,
289 sizeof(private_bytes))
290 || !EVP_DigestUpdate(mdctx, message, message_len)
291 || !EVP_DigestUpdate(mdctx, random_bytes, sizeof(random_bytes))
292 || !EVP_DigestFinal_ex(mdctx, digest, NULL))
293 goto err;
294
295 todo = num_k_bytes - done;
296 if (todo > SHA512_DIGEST_LENGTH)
297 todo = SHA512_DIGEST_LENGTH;
298 memcpy(k_bytes + done, digest, todo);
299 done += todo;
300 }
301
302 if (!BN_bin2bn(k_bytes, num_k_bytes, out))
303 goto err;
304 if (BN_mod(out, out, range, ctx) != 1)
305 goto err;
306 ret = 1;
307
308 err:
309 EVP_MD_CTX_free(mdctx);
310 EVP_MD_free(md);
311 OPENSSL_free(k_bytes);
312 OPENSSL_cleanse(private_bytes, sizeof(private_bytes));
313 return ret;
314}
315