1 /*
2 * Copyright 1995-2019 The OpenSSL Project Authors. All Rights Reserved.
3 *
4 * Licensed under the OpenSSL license (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 "bn_local.h"
14 #include <openssl/rand.h>
15 #include <openssl/sha.h>
16
17 typedef enum bnrand_flag_e {
18 NORMAL, TESTING, PRIVATE
19 } BNRAND_FLAG;
20
bnrand(BNRAND_FLAG flag,BIGNUM * rnd,int bits,int top,int bottom)21 static int bnrand(BNRAND_FLAG flag, BIGNUM *rnd, int bits, int top, int bottom)
22 {
23 unsigned char *buf = NULL;
24 int b, ret = 0, bit, bytes, mask;
25
26 if (bits == 0) {
27 if (top != BN_RAND_TOP_ANY || bottom != BN_RAND_BOTTOM_ANY)
28 goto toosmall;
29 BN_zero(rnd);
30 return 1;
31 }
32 if (bits < 0 || (bits == 1 && top > 0))
33 goto toosmall;
34
35 bytes = (bits + 7) / 8;
36 bit = (bits - 1) % 8;
37 mask = 0xff << (bit + 1);
38
39 buf = OPENSSL_malloc(bytes);
40 if (buf == NULL) {
41 BNerr(BN_F_BNRAND, ERR_R_MALLOC_FAILURE);
42 goto err;
43 }
44
45 /* make a random number and set the top and bottom bits */
46 b = flag == NORMAL ? RAND_bytes(buf, bytes) : RAND_priv_bytes(buf, bytes);
47 if (b <= 0)
48 goto err;
49
50 if (flag == TESTING) {
51 /*
52 * generate patterns that are more likely to trigger BN library bugs
53 */
54 int i;
55 unsigned char c;
56
57 for (i = 0; i < bytes; i++) {
58 if (RAND_bytes(&c, 1) <= 0)
59 goto err;
60 if (c >= 128 && i > 0)
61 buf[i] = buf[i - 1];
62 else if (c < 42)
63 buf[i] = 0;
64 else if (c < 84)
65 buf[i] = 255;
66 }
67 }
68
69 if (top >= 0) {
70 if (top) {
71 if (bit == 0) {
72 buf[0] = 1;
73 buf[1] |= 0x80;
74 } else {
75 buf[0] |= (3 << (bit - 1));
76 }
77 } else {
78 buf[0] |= (1 << bit);
79 }
80 }
81 buf[0] &= ~mask;
82 if (bottom) /* set bottom bit if requested */
83 buf[bytes - 1] |= 1;
84 if (!BN_bin2bn(buf, bytes, rnd))
85 goto err;
86 ret = 1;
87 err:
88 OPENSSL_clear_free(buf, bytes);
89 bn_check_top(rnd);
90 return ret;
91
92 toosmall:
93 BNerr(BN_F_BNRAND, BN_R_BITS_TOO_SMALL);
94 return 0;
95 }
96
BN_rand(BIGNUM * rnd,int bits,int top,int bottom)97 int BN_rand(BIGNUM *rnd, int bits, int top, int bottom)
98 {
99 return bnrand(NORMAL, rnd, bits, top, bottom);
100 }
101
BN_bntest_rand(BIGNUM * rnd,int bits,int top,int bottom)102 int BN_bntest_rand(BIGNUM *rnd, int bits, int top, int bottom)
103 {
104 return bnrand(TESTING, rnd, bits, top, bottom);
105 }
106
BN_priv_rand(BIGNUM * rnd,int bits,int top,int bottom)107 int BN_priv_rand(BIGNUM *rnd, int bits, int top, int bottom)
108 {
109 return bnrand(PRIVATE, rnd, bits, top, bottom);
110 }
111
112 /* random number r: 0 <= r < range */
bnrand_range(BNRAND_FLAG flag,BIGNUM * r,const BIGNUM * range)113 static int bnrand_range(BNRAND_FLAG flag, BIGNUM *r, const BIGNUM *range)
114 {
115 int n;
116 int count = 100;
117
118 if (range->neg || BN_is_zero(range)) {
119 BNerr(BN_F_BNRAND_RANGE, BN_R_INVALID_RANGE);
120 return 0;
121 }
122
123 n = BN_num_bits(range); /* n > 0 */
124
125 /* BN_is_bit_set(range, n - 1) always holds */
126
127 if (n == 1)
128 BN_zero(r);
129 else if (!BN_is_bit_set(range, n - 2) && !BN_is_bit_set(range, n - 3)) {
130 /*
131 * range = 100..._2, so 3*range (= 11..._2) is exactly one bit longer
132 * than range
133 */
134 do {
135 if (!bnrand(flag, r, n + 1, BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY))
136 return 0;
137
138 /*
139 * If r < 3*range, use r := r MOD range (which is either r, r -
140 * range, or r - 2*range). Otherwise, iterate once more. Since
141 * 3*range = 11..._2, each iteration succeeds with probability >=
142 * .75.
143 */
144 if (BN_cmp(r, range) >= 0) {
145 if (!BN_sub(r, r, range))
146 return 0;
147 if (BN_cmp(r, range) >= 0)
148 if (!BN_sub(r, r, range))
149 return 0;
150 }
151
152 if (!--count) {
153 BNerr(BN_F_BNRAND_RANGE, BN_R_TOO_MANY_ITERATIONS);
154 return 0;
155 }
156
157 }
158 while (BN_cmp(r, range) >= 0);
159 } else {
160 do {
161 /* range = 11..._2 or range = 101..._2 */
162 if (!bnrand(flag, r, n, BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY))
163 return 0;
164
165 if (!--count) {
166 BNerr(BN_F_BNRAND_RANGE, BN_R_TOO_MANY_ITERATIONS);
167 return 0;
168 }
169 }
170 while (BN_cmp(r, range) >= 0);
171 }
172
173 bn_check_top(r);
174 return 1;
175 }
176
BN_rand_range(BIGNUM * r,const BIGNUM * range)177 int BN_rand_range(BIGNUM *r, const BIGNUM *range)
178 {
179 return bnrand_range(NORMAL, r, range);
180 }
181
BN_priv_rand_range(BIGNUM * r,const BIGNUM * range)182 int BN_priv_rand_range(BIGNUM *r, const BIGNUM *range)
183 {
184 return bnrand_range(PRIVATE, r, range);
185 }
186
BN_pseudo_rand(BIGNUM * rnd,int bits,int top,int bottom)187 int BN_pseudo_rand(BIGNUM *rnd, int bits, int top, int bottom)
188 {
189 return BN_rand(rnd, bits, top, bottom);
190 }
191
BN_pseudo_rand_range(BIGNUM * r,const BIGNUM * range)192 int BN_pseudo_rand_range(BIGNUM *r, const BIGNUM *range)
193 {
194 return BN_rand_range(r, range);
195 }
196
197 /*
198 * BN_generate_dsa_nonce generates a random number 0 <= out < range. Unlike
199 * BN_rand_range, it also includes the contents of |priv| and |message| in
200 * the generation so that an RNG failure isn't fatal as long as |priv|
201 * remains secret. This is intended for use in DSA and ECDSA where an RNG
202 * weakness leads directly to private key exposure unless this function is
203 * used.
204 */
BN_generate_dsa_nonce(BIGNUM * out,const BIGNUM * range,const BIGNUM * priv,const unsigned char * message,size_t message_len,BN_CTX * ctx)205 int BN_generate_dsa_nonce(BIGNUM *out, const BIGNUM *range,
206 const BIGNUM *priv, const unsigned char *message,
207 size_t message_len, BN_CTX *ctx)
208 {
209 SHA512_CTX sha;
210 /*
211 * We use 512 bits of random data per iteration to ensure that we have at
212 * least |range| bits of randomness.
213 */
214 unsigned char random_bytes[64];
215 unsigned char digest[SHA512_DIGEST_LENGTH];
216 unsigned done, todo;
217 /* We generate |range|+8 bytes of random output. */
218 const unsigned num_k_bytes = BN_num_bytes(range) + 8;
219 unsigned char private_bytes[96];
220 unsigned char *k_bytes;
221 int ret = 0;
222
223 k_bytes = OPENSSL_malloc(num_k_bytes);
224 if (k_bytes == NULL)
225 goto err;
226
227 /* We copy |priv| into a local buffer to avoid exposing its length. */
228 if (BN_bn2binpad(priv, private_bytes, sizeof(private_bytes)) < 0) {
229 /*
230 * No reasonable DSA or ECDSA key should have a private key this
231 * large and we don't handle this case in order to avoid leaking the
232 * length of the private key.
233 */
234 BNerr(BN_F_BN_GENERATE_DSA_NONCE, BN_R_PRIVATE_KEY_TOO_LARGE);
235 goto err;
236 }
237
238 for (done = 0; done < num_k_bytes;) {
239 if (RAND_priv_bytes(random_bytes, sizeof(random_bytes)) != 1)
240 goto err;
241 SHA512_Init(&sha);
242 SHA512_Update(&sha, &done, sizeof(done));
243 SHA512_Update(&sha, private_bytes, sizeof(private_bytes));
244 SHA512_Update(&sha, message, message_len);
245 SHA512_Update(&sha, random_bytes, sizeof(random_bytes));
246 SHA512_Final(digest, &sha);
247
248 todo = num_k_bytes - done;
249 if (todo > SHA512_DIGEST_LENGTH)
250 todo = SHA512_DIGEST_LENGTH;
251 memcpy(k_bytes + done, digest, todo);
252 done += todo;
253 }
254
255 if (!BN_bin2bn(k_bytes, num_k_bytes, out))
256 goto err;
257 if (BN_mod(out, out, range, ctx) != 1)
258 goto err;
259 ret = 1;
260
261 err:
262 OPENSSL_free(k_bytes);
263 OPENSSL_cleanse(private_bytes, sizeof(private_bytes));
264 return ret;
265 }
266