1 /*
2 * Copyright 1995-2024 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,
21 TESTING,
22 PRIVATE
23 } BNRAND_FLAG;
24
bnrand(BNRAND_FLAG flag,BIGNUM * rnd,int bits,int top,int bottom,unsigned int strength,BN_CTX * ctx)25 static int bnrand(BNRAND_FLAG flag, BIGNUM *rnd, int bits, int top, int bottom,
26 unsigned int strength, BN_CTX *ctx)
27 {
28 unsigned char *buf = NULL;
29 int b, ret = 0, bit, bytes, mask;
30 OSSL_LIB_CTX *libctx = ossl_bn_get_libctx(ctx);
31
32 if (bits == 0) {
33 if (top != BN_RAND_TOP_ANY || bottom != BN_RAND_BOTTOM_ANY)
34 goto toosmall;
35 BN_zero(rnd);
36 return 1;
37 }
38 if (bits < 0 || (bits == 1 && top > 0))
39 goto toosmall;
40
41 bytes = (bits + 7) / 8;
42 bit = (bits - 1) % 8;
43 mask = 0xff << (bit + 1);
44
45 buf = OPENSSL_malloc(bytes);
46 if (buf == NULL)
47 goto err;
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 } while (BN_cmp(r, range) >= 0);
185 } else {
186 do {
187 /* range = 11..._2 or range = 101..._2 */
188 if (!bnrand(flag, r, n, BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY,
189 strength, ctx))
190 return 0;
191
192 if (!--count) {
193 ERR_raise(ERR_LIB_BN, BN_R_TOO_MANY_ITERATIONS);
194 return 0;
195 }
196 } while (BN_cmp(r, range) >= 0);
197 }
198
199 bn_check_top(r);
200 return 1;
201 }
202
BN_rand_range_ex(BIGNUM * r,const BIGNUM * range,unsigned int strength,BN_CTX * ctx)203 int BN_rand_range_ex(BIGNUM *r, const BIGNUM *range, unsigned int strength,
204 BN_CTX *ctx)
205 {
206 return bnrand_range(NORMAL, r, range, strength, ctx);
207 }
208
209 #ifndef FIPS_MODULE
BN_rand_range(BIGNUM * r,const BIGNUM * range)210 int BN_rand_range(BIGNUM *r, const BIGNUM *range)
211 {
212 return bnrand_range(NORMAL, r, range, 0, NULL);
213 }
214 #endif
215
BN_priv_rand_range_ex(BIGNUM * r,const BIGNUM * range,unsigned int strength,BN_CTX * ctx)216 int BN_priv_rand_range_ex(BIGNUM *r, const BIGNUM *range, unsigned int strength,
217 BN_CTX *ctx)
218 {
219 return bnrand_range(PRIVATE, r, range, strength, ctx);
220 }
221
222 #ifndef FIPS_MODULE
BN_priv_rand_range(BIGNUM * r,const BIGNUM * range)223 int BN_priv_rand_range(BIGNUM *r, const BIGNUM *range)
224 {
225 return bnrand_range(PRIVATE, r, range, 0, NULL);
226 }
227
228 #ifndef OPENSSL_NO_DEPRECATED_3_0
BN_pseudo_rand(BIGNUM * rnd,int bits,int top,int bottom)229 int BN_pseudo_rand(BIGNUM *rnd, int bits, int top, int bottom)
230 {
231 return BN_rand(rnd, bits, top, bottom);
232 }
233
BN_pseudo_rand_range(BIGNUM * r,const BIGNUM * range)234 int BN_pseudo_rand_range(BIGNUM *r, const BIGNUM *range)
235 {
236 return BN_rand_range(r, range);
237 }
238 #endif
239 #endif
240
ossl_bn_priv_rand_range_fixed_top(BIGNUM * r,const BIGNUM * range,unsigned int strength,BN_CTX * ctx)241 int ossl_bn_priv_rand_range_fixed_top(BIGNUM *r, const BIGNUM *range,
242 unsigned int strength, BN_CTX *ctx)
243 {
244 int n;
245 int count = 100;
246
247 if (r == NULL) {
248 ERR_raise(ERR_LIB_BN, ERR_R_PASSED_NULL_PARAMETER);
249 return 0;
250 }
251
252 if (range->neg || BN_is_zero(range)) {
253 ERR_raise(ERR_LIB_BN, BN_R_INVALID_RANGE);
254 return 0;
255 }
256
257 n = BN_num_bits(range); /* n > 0 */
258
259 /* BN_is_bit_set(range, n - 1) always holds */
260
261 if (n == 1) {
262 BN_zero(r);
263 } else {
264 BN_set_flags(r, BN_FLG_CONSTTIME);
265 do {
266 if (!bnrand(PRIVATE, r, n + 1, BN_RAND_TOP_ONE, BN_RAND_BOTTOM_ANY,
267 strength, ctx))
268 return 0;
269
270 if (!--count) {
271 ERR_raise(ERR_LIB_BN, BN_R_TOO_MANY_ITERATIONS);
272 return 0;
273 }
274 ossl_bn_mask_bits_fixed_top(r, n);
275 } while (BN_ucmp(r, range) >= 0);
276 #ifdef BN_DEBUG
277 /* With BN_DEBUG on a fixed top number cannot be returned */
278 bn_correct_top(r);
279 #endif
280 }
281
282 return 1;
283 }
284
285 /*
286 * ossl_bn_gen_dsa_nonce_fixed_top generates a random number 0 <= out < range.
287 * Unlike BN_rand_range, it also includes the contents of |priv| and |message|
288 * in the generation so that an RNG failure isn't fatal as long as |priv|
289 * remains secret. This is intended for use in DSA and ECDSA where an RNG
290 * weakness leads directly to private key exposure unless this function is
291 * used.
292 */
ossl_bn_gen_dsa_nonce_fixed_top(BIGNUM * out,const BIGNUM * range,const BIGNUM * priv,const unsigned char * message,size_t message_len,BN_CTX * ctx)293 int ossl_bn_gen_dsa_nonce_fixed_top(BIGNUM *out, const BIGNUM *range,
294 const BIGNUM *priv,
295 const unsigned char *message,
296 size_t message_len, BN_CTX *ctx)
297 {
298 EVP_MD_CTX *mdctx = EVP_MD_CTX_new();
299 /*
300 * We use 512 bits of random data per iteration to ensure that we have at
301 * least |range| bits of randomness.
302 */
303 unsigned char random_bytes[64];
304 unsigned char digest[SHA512_DIGEST_LENGTH];
305 unsigned done, todo;
306 /* We generate |range|+1 bytes of random output. */
307 const unsigned num_k_bytes = BN_num_bytes(range) + 1;
308 unsigned char private_bytes[96];
309 unsigned char *k_bytes = NULL;
310 const int max_n = 64; /* Pr(failure to generate) < 2^max_n */
311 int n;
312 int ret = 0;
313 EVP_MD *md = NULL;
314 OSSL_LIB_CTX *libctx = ossl_bn_get_libctx(ctx);
315
316 if (mdctx == NULL)
317 goto end;
318
319 k_bytes = OPENSSL_malloc(num_k_bytes);
320 if (k_bytes == NULL)
321 goto end;
322 /* Ensure top byte is set to avoid non-constant time in bin2bn */
323 k_bytes[0] = 0xff;
324
325 /* We copy |priv| into a local buffer to avoid exposing its length. */
326 if (BN_bn2binpad(priv, private_bytes, sizeof(private_bytes)) < 0) {
327 /*
328 * No reasonable DSA or ECDSA key should have a private key this
329 * large and we don't handle this case in order to avoid leaking the
330 * length of the private key.
331 */
332 ERR_raise(ERR_LIB_BN, BN_R_PRIVATE_KEY_TOO_LARGE);
333 goto end;
334 }
335
336 md = EVP_MD_fetch(libctx, "SHA512", NULL);
337 if (md == NULL) {
338 ERR_raise(ERR_LIB_BN, BN_R_NO_SUITABLE_DIGEST);
339 goto end;
340 }
341 for (n = 0; n < max_n; n++) {
342 unsigned char i = 0;
343
344 for (done = 1; done < num_k_bytes;) {
345 if (RAND_priv_bytes_ex(libctx, random_bytes, sizeof(random_bytes),
346 0)
347 <= 0)
348 goto end;
349
350 if (!EVP_DigestInit_ex(mdctx, md, NULL)
351 || !EVP_DigestUpdate(mdctx, &i, sizeof(i))
352 || !EVP_DigestUpdate(mdctx, private_bytes,
353 sizeof(private_bytes))
354 || !EVP_DigestUpdate(mdctx, message, message_len)
355 || !EVP_DigestUpdate(mdctx, random_bytes,
356 sizeof(random_bytes))
357 || !EVP_DigestFinal_ex(mdctx, digest, NULL))
358 goto end;
359
360 todo = num_k_bytes - done;
361 if (todo > SHA512_DIGEST_LENGTH)
362 todo = SHA512_DIGEST_LENGTH;
363 memcpy(k_bytes + done, digest, todo);
364 done += todo;
365 ++i;
366 }
367
368 if (!BN_bin2bn(k_bytes, num_k_bytes, out))
369 goto end;
370
371 /* Clear out the top bits and rejection filter into range */
372 BN_set_flags(out, BN_FLG_CONSTTIME);
373 ossl_bn_mask_bits_fixed_top(out, BN_num_bits(range));
374
375 if (BN_ucmp(out, range) < 0) {
376 ret = 1;
377 #ifdef BN_DEBUG
378 /* With BN_DEBUG on a fixed top number cannot be returned */
379 bn_correct_top(out);
380 #endif
381 goto end;
382 }
383 }
384 /* Failed to generate anything */
385 ERR_raise(ERR_LIB_BN, ERR_R_INTERNAL_ERROR);
386
387 end:
388 EVP_MD_CTX_free(mdctx);
389 EVP_MD_free(md);
390 OPENSSL_clear_free(k_bytes, num_k_bytes);
391 OPENSSL_cleanse(digest, sizeof(digest));
392 OPENSSL_cleanse(random_bytes, sizeof(random_bytes));
393 OPENSSL_cleanse(private_bytes, sizeof(private_bytes));
394 return ret;
395 }
396
BN_generate_dsa_nonce(BIGNUM * out,const BIGNUM * range,const BIGNUM * priv,const unsigned char * message,size_t message_len,BN_CTX * ctx)397 int BN_generate_dsa_nonce(BIGNUM *out, const BIGNUM *range,
398 const BIGNUM *priv, const unsigned char *message,
399 size_t message_len, BN_CTX *ctx)
400 {
401 int ret;
402
403 ret = ossl_bn_gen_dsa_nonce_fixed_top(out, range, priv, message,
404 message_len, ctx);
405 /*
406 * This call makes the BN_generate_dsa_nonce non-const-time, thus we
407 * do not use it internally. But fixed_top BNs currently cannot be returned
408 * from public API calls.
409 */
410 bn_correct_top(out);
411 return ret;
412 }
413