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, 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 goto err;
46
47 /* make a random number and set the top and bottom bits */
48 b = flag == NORMAL ? RAND_bytes_ex(libctx, buf, bytes, strength)
49 : RAND_priv_bytes_ex(libctx, buf, bytes, strength);
50 if (b <= 0)
51 goto err;
52
53 if (flag == TESTING) {
54 /*
55 * generate patterns that are more likely to trigger BN library bugs
56 */
57 int i;
58 unsigned char c;
59
60 for (i = 0; i < bytes; i++) {
61 if (RAND_bytes_ex(libctx, &c, 1, strength) <= 0)
62 goto err;
63 if (c >= 128 && i > 0)
64 buf[i] = buf[i - 1];
65 else if (c < 42)
66 buf[i] = 0;
67 else if (c < 84)
68 buf[i] = 255;
69 }
70 }
71
72 if (top >= 0) {
73 if (top) {
74 if (bit == 0) {
75 buf[0] = 1;
76 buf[1] |= 0x80;
77 } else {
78 buf[0] |= (3 << (bit - 1));
79 }
80 } else {
81 buf[0] |= (1 << bit);
82 }
83 }
84 buf[0] &= ~mask;
85 if (bottom) /* set bottom bit if requested */
86 buf[bytes - 1] |= 1;
87 if (!BN_bin2bn(buf, bytes, rnd))
88 goto err;
89 ret = 1;
90 err:
91 OPENSSL_clear_free(buf, bytes);
92 bn_check_top(rnd);
93 return ret;
94
95 toosmall:
96 ERR_raise(ERR_LIB_BN, BN_R_BITS_TOO_SMALL);
97 return 0;
98 }
99
BN_rand_ex(BIGNUM * rnd,int bits,int top,int bottom,unsigned int strength,BN_CTX * ctx)100 int BN_rand_ex(BIGNUM *rnd, int bits, int top, int bottom,
101 unsigned int strength, BN_CTX *ctx)
102 {
103 return bnrand(NORMAL, rnd, bits, top, bottom, strength, ctx);
104 }
105 #ifndef FIPS_MODULE
BN_rand(BIGNUM * rnd,int bits,int top,int bottom)106 int BN_rand(BIGNUM *rnd, int bits, int top, int bottom)
107 {
108 return bnrand(NORMAL, rnd, bits, top, bottom, 0, NULL);
109 }
110
BN_bntest_rand(BIGNUM * rnd,int bits,int top,int bottom)111 int BN_bntest_rand(BIGNUM *rnd, int bits, int top, int bottom)
112 {
113 return bnrand(TESTING, rnd, bits, top, bottom, 0, NULL);
114 }
115 #endif
116
BN_priv_rand_ex(BIGNUM * rnd,int bits,int top,int bottom,unsigned int strength,BN_CTX * ctx)117 int BN_priv_rand_ex(BIGNUM *rnd, int bits, int top, int bottom,
118 unsigned int strength, BN_CTX *ctx)
119 {
120 return bnrand(PRIVATE, rnd, bits, top, bottom, strength, ctx);
121 }
122
123 #ifndef FIPS_MODULE
BN_priv_rand(BIGNUM * rnd,int bits,int top,int bottom)124 int BN_priv_rand(BIGNUM *rnd, int bits, int top, int bottom)
125 {
126 return bnrand(PRIVATE, rnd, bits, top, bottom, 0, NULL);
127 }
128 #endif
129
130 /* random number r: 0 <= r < range */
bnrand_range(BNRAND_FLAG flag,BIGNUM * r,const BIGNUM * range,unsigned int strength,BN_CTX * ctx)131 static int bnrand_range(BNRAND_FLAG flag, BIGNUM *r, const BIGNUM *range,
132 unsigned int strength, BN_CTX *ctx)
133 {
134 int n;
135 int count = 100;
136
137 if (r == NULL) {
138 ERR_raise(ERR_LIB_BN, ERR_R_PASSED_NULL_PARAMETER);
139 return 0;
140 }
141
142 if (range->neg || BN_is_zero(range)) {
143 ERR_raise(ERR_LIB_BN, BN_R_INVALID_RANGE);
144 return 0;
145 }
146
147 n = BN_num_bits(range); /* n > 0 */
148
149 /* BN_is_bit_set(range, n - 1) always holds */
150
151 if (n == 1)
152 BN_zero(r);
153 else if (!BN_is_bit_set(range, n - 2) && !BN_is_bit_set(range, n - 3)) {
154 /*
155 * range = 100..._2, so 3*range (= 11..._2) is exactly one bit longer
156 * than range
157 */
158 do {
159 if (!bnrand(flag, r, n + 1, BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY,
160 strength, ctx))
161 return 0;
162
163 /*
164 * If r < 3*range, use r := r MOD range (which is either r, r -
165 * range, or r - 2*range). Otherwise, iterate once more. Since
166 * 3*range = 11..._2, each iteration succeeds with probability >=
167 * .75.
168 */
169 if (BN_cmp(r, range) >= 0) {
170 if (!BN_sub(r, r, range))
171 return 0;
172 if (BN_cmp(r, range) >= 0)
173 if (!BN_sub(r, r, range))
174 return 0;
175 }
176
177 if (!--count) {
178 ERR_raise(ERR_LIB_BN, BN_R_TOO_MANY_ITERATIONS);
179 return 0;
180 }
181
182 }
183 while (BN_cmp(r, range) >= 0);
184 } else {
185 do {
186 /* range = 11..._2 or range = 101..._2 */
187 if (!bnrand(flag, r, n, BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY,
188 strength, ctx))
189 return 0;
190
191 if (!--count) {
192 ERR_raise(ERR_LIB_BN, BN_R_TOO_MANY_ITERATIONS);
193 return 0;
194 }
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 }
276 while (BN_ucmp(r, range) >= 0);
277 #ifdef BN_DEBUG
278 /* With BN_DEBUG on a fixed top number cannot be returned */
279 bn_correct_top(r);
280 #endif
281 }
282
283 return 1;
284 }
285
286 /*
287 * ossl_bn_gen_dsa_nonce_fixed_top generates a random number 0 <= out < range.
288 * Unlike BN_rand_range, it also includes the contents of |priv| and |message|
289 * in the generation so that an RNG failure isn't fatal as long as |priv|
290 * remains secret. This is intended for use in DSA and ECDSA where an RNG
291 * weakness leads directly to private key exposure unless this function is
292 * used.
293 */
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)294 int ossl_bn_gen_dsa_nonce_fixed_top(BIGNUM *out, const BIGNUM *range,
295 const BIGNUM *priv,
296 const unsigned char *message,
297 size_t message_len, BN_CTX *ctx)
298 {
299 EVP_MD_CTX *mdctx = EVP_MD_CTX_new();
300 /*
301 * We use 512 bits of random data per iteration to ensure that we have at
302 * least |range| bits of randomness.
303 */
304 unsigned char random_bytes[64];
305 unsigned char digest[SHA512_DIGEST_LENGTH];
306 unsigned done, todo;
307 /* We generate |range|+1 bytes of random output. */
308 const unsigned num_k_bytes = BN_num_bytes(range) + 1;
309 unsigned char private_bytes[96];
310 unsigned char *k_bytes = NULL;
311 const int max_n = 64; /* Pr(failure to generate) < 2^max_n */
312 int n;
313 int ret = 0;
314 EVP_MD *md = NULL;
315 OSSL_LIB_CTX *libctx = ossl_bn_get_libctx(ctx);
316
317 if (mdctx == NULL)
318 goto end;
319
320 k_bytes = OPENSSL_malloc(num_k_bytes);
321 if (k_bytes == NULL)
322 goto end;
323 /* Ensure top byte is set to avoid non-constant time in bin2bn */
324 k_bytes[0] = 0xff;
325
326 /* We copy |priv| into a local buffer to avoid exposing its length. */
327 if (BN_bn2binpad(priv, private_bytes, sizeof(private_bytes)) < 0) {
328 /*
329 * No reasonable DSA or ECDSA key should have a private key this
330 * large and we don't handle this case in order to avoid leaking the
331 * length of the private key.
332 */
333 ERR_raise(ERR_LIB_BN, BN_R_PRIVATE_KEY_TOO_LARGE);
334 goto end;
335 }
336
337 md = EVP_MD_fetch(libctx, "SHA512", NULL);
338 if (md == NULL) {
339 ERR_raise(ERR_LIB_BN, BN_R_NO_SUITABLE_DIGEST);
340 goto end;
341 }
342 for (n = 0; n < max_n; n++) {
343 unsigned char i = 0;
344
345 for (done = 1; done < num_k_bytes;) {
346 if (RAND_priv_bytes_ex(libctx, random_bytes, sizeof(random_bytes),
347 0) <= 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