1 /*
2 * Copyright 1995-2023 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
19 typedef enum bnrand_flag_e {
20 NORMAL, TESTING, PRIVATE
21 } BNRAND_FLAG;
22
bnrand(BNRAND_FLAG flag,BIGNUM * rnd,int bits,int top,int bottom,unsigned int strength,BN_CTX * ctx)23 static int bnrand(BNRAND_FLAG flag, BIGNUM *rnd, int bits, int top, int bottom,
24 unsigned int strength, BN_CTX *ctx)
25 {
26 unsigned char *buf = NULL;
27 int b, ret = 0, bit, bytes, mask;
28 OSSL_LIB_CTX *libctx = ossl_bn_get_libctx(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 ERR_raise(ERR_LIB_BN, 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, strength)
51 : RAND_priv_bytes_ex(libctx, buf, bytes, strength);
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, strength) <= 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
97 toosmall:
98 ERR_raise(ERR_LIB_BN, BN_R_BITS_TOO_SMALL);
99 return 0;
100 }
101
BN_rand_ex(BIGNUM * rnd,int bits,int top,int bottom,unsigned int strength,BN_CTX * ctx)102 int BN_rand_ex(BIGNUM *rnd, int bits, int top, int bottom,
103 unsigned int strength, BN_CTX *ctx)
104 {
105 return bnrand(NORMAL, rnd, bits, top, bottom, strength, ctx);
106 }
107 #ifndef FIPS_MODULE
BN_rand(BIGNUM * rnd,int bits,int top,int bottom)108 int BN_rand(BIGNUM *rnd, int bits, int top, int bottom)
109 {
110 return bnrand(NORMAL, rnd, bits, top, bottom, 0, NULL);
111 }
112
BN_bntest_rand(BIGNUM * rnd,int bits,int top,int bottom)113 int BN_bntest_rand(BIGNUM *rnd, int bits, int top, int bottom)
114 {
115 return bnrand(TESTING, rnd, bits, top, bottom, 0, NULL);
116 }
117 #endif
118
BN_priv_rand_ex(BIGNUM * rnd,int bits,int top,int bottom,unsigned int strength,BN_CTX * ctx)119 int BN_priv_rand_ex(BIGNUM *rnd, int bits, int top, int bottom,
120 unsigned int strength, BN_CTX *ctx)
121 {
122 return bnrand(PRIVATE, rnd, bits, top, bottom, strength, ctx);
123 }
124
125 #ifndef FIPS_MODULE
BN_priv_rand(BIGNUM * rnd,int bits,int top,int bottom)126 int BN_priv_rand(BIGNUM *rnd, int bits, int top, int bottom)
127 {
128 return bnrand(PRIVATE, rnd, bits, top, bottom, 0, NULL);
129 }
130 #endif
131
132 /* random number r: 0 <= r < range */
bnrand_range(BNRAND_FLAG flag,BIGNUM * r,const BIGNUM * range,unsigned int strength,BN_CTX * ctx)133 static int bnrand_range(BNRAND_FLAG flag, BIGNUM *r, const BIGNUM *range,
134 unsigned int strength, BN_CTX *ctx)
135 {
136 int n;
137 int count = 100;
138
139 if (r == NULL) {
140 ERR_raise(ERR_LIB_BN, ERR_R_PASSED_NULL_PARAMETER);
141 return 0;
142 }
143
144 if (range->neg || BN_is_zero(range)) {
145 ERR_raise(ERR_LIB_BN, BN_R_INVALID_RANGE);
146 return 0;
147 }
148
149 n = BN_num_bits(range); /* n > 0 */
150
151 /* BN_is_bit_set(range, n - 1) always holds */
152
153 if (n == 1)
154 BN_zero(r);
155 else if (!BN_is_bit_set(range, n - 2) && !BN_is_bit_set(range, n - 3)) {
156 /*
157 * range = 100..._2, so 3*range (= 11..._2) is exactly one bit longer
158 * than range
159 */
160 do {
161 if (!bnrand(flag, r, n + 1, BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY,
162 strength, ctx))
163 return 0;
164
165 /*
166 * If r < 3*range, use r := r MOD range (which is either r, r -
167 * range, or r - 2*range). Otherwise, iterate once more. Since
168 * 3*range = 11..._2, each iteration succeeds with probability >=
169 * .75.
170 */
171 if (BN_cmp(r, range) >= 0) {
172 if (!BN_sub(r, r, range))
173 return 0;
174 if (BN_cmp(r, range) >= 0)
175 if (!BN_sub(r, r, range))
176 return 0;
177 }
178
179 if (!--count) {
180 ERR_raise(ERR_LIB_BN, BN_R_TOO_MANY_ITERATIONS);
181 return 0;
182 }
183
184 }
185 while (BN_cmp(r, range) >= 0);
186 } else {
187 do {
188 /* range = 11..._2 or range = 101..._2 */
189 if (!bnrand(flag, r, n, BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY, 0,
190 ctx))
191 return 0;
192
193 if (!--count) {
194 ERR_raise(ERR_LIB_BN, BN_R_TOO_MANY_ITERATIONS);
195 return 0;
196 }
197 }
198 while (BN_cmp(r, range) >= 0);
199 }
200
201 bn_check_top(r);
202 return 1;
203 }
204
BN_rand_range_ex(BIGNUM * r,const BIGNUM * range,unsigned int strength,BN_CTX * ctx)205 int BN_rand_range_ex(BIGNUM *r, const BIGNUM *range, unsigned int strength,
206 BN_CTX *ctx)
207 {
208 return bnrand_range(NORMAL, r, range, strength, ctx);
209 }
210
211 #ifndef FIPS_MODULE
BN_rand_range(BIGNUM * r,const BIGNUM * range)212 int BN_rand_range(BIGNUM *r, const BIGNUM *range)
213 {
214 return bnrand_range(NORMAL, r, range, 0, NULL);
215 }
216 #endif
217
BN_priv_rand_range_ex(BIGNUM * r,const BIGNUM * range,unsigned int strength,BN_CTX * ctx)218 int BN_priv_rand_range_ex(BIGNUM *r, const BIGNUM *range, unsigned int strength,
219 BN_CTX *ctx)
220 {
221 return bnrand_range(PRIVATE, r, range, strength, ctx);
222 }
223
224 #ifndef FIPS_MODULE
BN_priv_rand_range(BIGNUM * r,const BIGNUM * range)225 int BN_priv_rand_range(BIGNUM *r, const BIGNUM *range)
226 {
227 return bnrand_range(PRIVATE, r, range, 0, NULL);
228 }
229
230 # ifndef OPENSSL_NO_DEPRECATED_3_0
BN_pseudo_rand(BIGNUM * rnd,int bits,int top,int bottom)231 int BN_pseudo_rand(BIGNUM *rnd, int bits, int top, int bottom)
232 {
233 return BN_rand(rnd, bits, top, bottom);
234 }
235
BN_pseudo_rand_range(BIGNUM * r,const BIGNUM * range)236 int BN_pseudo_rand_range(BIGNUM *r, const BIGNUM *range)
237 {
238 return BN_rand_range(r, range);
239 }
240 # endif
241 #endif
242
243 /*
244 * BN_generate_dsa_nonce generates a random number 0 <= out < range. Unlike
245 * BN_rand_range, it also includes the contents of |priv| and |message| in
246 * the generation so that an RNG failure isn't fatal as long as |priv|
247 * remains secret. This is intended for use in DSA and ECDSA where an RNG
248 * weakness leads directly to private key exposure unless this function is
249 * used.
250 */
BN_generate_dsa_nonce(BIGNUM * out,const BIGNUM * range,const BIGNUM * priv,const unsigned char * message,size_t message_len,BN_CTX * ctx)251 int BN_generate_dsa_nonce(BIGNUM *out, const BIGNUM *range,
252 const BIGNUM *priv, const unsigned char *message,
253 size_t message_len, BN_CTX *ctx)
254 {
255 EVP_MD_CTX *mdctx = EVP_MD_CTX_new();
256 /*
257 * We use 512 bits of random data per iteration to ensure that we have at
258 * least |range| bits of randomness.
259 */
260 unsigned char random_bytes[64];
261 unsigned char digest[SHA512_DIGEST_LENGTH];
262 unsigned done, todo;
263 /* We generate |range|+8 bytes of random output. */
264 const unsigned num_k_bytes = BN_num_bytes(range) + 8;
265 unsigned char private_bytes[96];
266 unsigned char *k_bytes = NULL;
267 int ret = 0;
268 EVP_MD *md = NULL;
269 OSSL_LIB_CTX *libctx = ossl_bn_get_libctx(ctx);
270
271 if (mdctx == NULL)
272 goto err;
273
274 k_bytes = OPENSSL_malloc(num_k_bytes);
275 if (k_bytes == NULL)
276 goto err;
277
278 /* We copy |priv| into a local buffer to avoid exposing its length. */
279 if (BN_bn2binpad(priv, private_bytes, sizeof(private_bytes)) < 0) {
280 /*
281 * No reasonable DSA or ECDSA key should have a private key this
282 * large and we don't handle this case in order to avoid leaking the
283 * length of the private key.
284 */
285 ERR_raise(ERR_LIB_BN, BN_R_PRIVATE_KEY_TOO_LARGE);
286 goto err;
287 }
288
289 md = EVP_MD_fetch(libctx, "SHA512", NULL);
290 if (md == NULL) {
291 ERR_raise(ERR_LIB_BN, BN_R_NO_SUITABLE_DIGEST);
292 goto err;
293 }
294 for (done = 0; done < num_k_bytes;) {
295 if (RAND_priv_bytes_ex(libctx, random_bytes, sizeof(random_bytes), 0) <= 0)
296 goto err;
297
298 if (!EVP_DigestInit_ex(mdctx, md, NULL)
299 || !EVP_DigestUpdate(mdctx, &done, sizeof(done))
300 || !EVP_DigestUpdate(mdctx, private_bytes,
301 sizeof(private_bytes))
302 || !EVP_DigestUpdate(mdctx, message, message_len)
303 || !EVP_DigestUpdate(mdctx, random_bytes, sizeof(random_bytes))
304 || !EVP_DigestFinal_ex(mdctx, digest, NULL))
305 goto err;
306
307 todo = num_k_bytes - done;
308 if (todo > SHA512_DIGEST_LENGTH)
309 todo = SHA512_DIGEST_LENGTH;
310 memcpy(k_bytes + done, digest, todo);
311 done += todo;
312 }
313
314 if (!BN_bin2bn(k_bytes, num_k_bytes, out))
315 goto err;
316 if (BN_mod(out, out, range, ctx) != 1)
317 goto err;
318 ret = 1;
319
320 err:
321 EVP_MD_CTX_free(mdctx);
322 EVP_MD_free(md);
323 OPENSSL_clear_free(k_bytes, num_k_bytes);
324 OPENSSL_cleanse(digest, sizeof(digest));
325 OPENSSL_cleanse(random_bytes, sizeof(random_bytes));
326 OPENSSL_cleanse(private_bytes, sizeof(private_bytes));
327 return ret;
328 }
329