1 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
2 * All rights reserved.
3 *
4 * This package is an SSL implementation written
5 * by Eric Young (eay@cryptsoft.com).
6 * The implementation was written so as to conform with Netscapes SSL.
7 *
8 * This library is free for commercial and non-commercial use as long as
9 * the following conditions are aheared to. The following conditions
10 * apply to all code found in this distribution, be it the RC4, RSA,
11 * lhash, DES, etc., code; not just the SSL code. The SSL documentation
12 * included with this distribution is covered by the same copyright terms
13 * except that the holder is Tim Hudson (tjh@cryptsoft.com).
14 *
15 * Copyright remains Eric Young's, and as such any Copyright notices in
16 * the code are not to be removed.
17 * If this package is used in a product, Eric Young should be given attribution
18 * as the author of the parts of the library used.
19 * This can be in the form of a textual message at program startup or
20 * in documentation (online or textual) provided with the package.
21 *
22 * Redistribution and use in source and binary forms, with or without
23 * modification, are permitted provided that the following conditions
24 * are met:
25 * 1. Redistributions of source code must retain the copyright
26 * notice, this list of conditions and the following disclaimer.
27 * 2. Redistributions in binary form must reproduce the above copyright
28 * notice, this list of conditions and the following disclaimer in the
29 * documentation and/or other materials provided with the distribution.
30 * 3. All advertising materials mentioning features or use of this software
31 * must display the following acknowledgement:
32 * "This product includes cryptographic software written by
33 * Eric Young (eay@cryptsoft.com)"
34 * The word 'cryptographic' can be left out if the rouines from the library
35 * being used are not cryptographic related :-).
36 * 4. If you include any Windows specific code (or a derivative thereof) from
37 * the apps directory (application code) you must include an acknowledgement:
38 * "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
39 *
40 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
41 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
42 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
43 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
44 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
45 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
46 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
47 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
48 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
49 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
50 * SUCH DAMAGE.
51 *
52 * The licence and distribution terms for any publically available version or
53 * derivative of this code cannot be changed. i.e. this code cannot simply be
54 * copied and put under another distribution licence
55 * [including the GNU Public Licence.] */
56
57 #include <openssl/bn.h>
58
59 #include <assert.h>
60 #include <limits.h>
61
62 #include "internal.h"
63
64
BN_bin2bn(const uint8_t * in,size_t len,BIGNUM * ret)65 BIGNUM *BN_bin2bn(const uint8_t *in, size_t len, BIGNUM *ret) {
66 size_t num_words;
67 unsigned m;
68 BN_ULONG word = 0;
69 BIGNUM *bn = NULL;
70
71 if (ret == NULL) {
72 ret = bn = BN_new();
73 }
74
75 if (ret == NULL) {
76 return NULL;
77 }
78
79 if (len == 0) {
80 ret->top = 0;
81 return ret;
82 }
83
84 num_words = ((len - 1) / BN_BYTES) + 1;
85 m = (len - 1) % BN_BYTES;
86 if (!bn_wexpand(ret, num_words)) {
87 if (bn) {
88 BN_free(bn);
89 }
90 return NULL;
91 }
92
93 /* |bn_wexpand| must check bounds on |num_words| to write it into
94 * |ret->dmax|. */
95 assert(num_words <= INT_MAX);
96 ret->top = (int)num_words;
97 ret->neg = 0;
98
99 while (len--) {
100 word = (word << 8) | *(in++);
101 if (m-- == 0) {
102 ret->d[--num_words] = word;
103 word = 0;
104 m = BN_BYTES - 1;
105 }
106 }
107
108 /* need to call this due to clear byte at top if avoiding having the top bit
109 * set (-ve number) */
110 bn_correct_top(ret);
111 return ret;
112 }
113
BN_le2bn(const uint8_t * in,size_t len,BIGNUM * ret)114 BIGNUM *BN_le2bn(const uint8_t *in, size_t len, BIGNUM *ret) {
115 BIGNUM *bn = NULL;
116 if (ret == NULL) {
117 bn = BN_new();
118 ret = bn;
119 }
120
121 if (ret == NULL) {
122 return NULL;
123 }
124
125 if (len == 0) {
126 ret->top = 0;
127 ret->neg = 0;
128 return ret;
129 }
130
131 /* Reserve enough space in |ret|. */
132 size_t num_words = ((len - 1) / BN_BYTES) + 1;
133 if (!bn_wexpand(ret, num_words)) {
134 BN_free(bn);
135 return NULL;
136 }
137 ret->top = num_words;
138
139 /* Make sure the top bytes will be zeroed. */
140 ret->d[num_words - 1] = 0;
141
142 /* We only support little-endian platforms, so we can simply memcpy the
143 * internal representation. */
144 OPENSSL_memcpy(ret->d, in, len);
145
146 bn_correct_top(ret);
147 return ret;
148 }
149
BN_bn2bin(const BIGNUM * in,uint8_t * out)150 size_t BN_bn2bin(const BIGNUM *in, uint8_t *out) {
151 size_t n, i;
152 BN_ULONG l;
153
154 n = i = BN_num_bytes(in);
155 while (i--) {
156 l = in->d[i / BN_BYTES];
157 *(out++) = (unsigned char)(l >> (8 * (i % BN_BYTES))) & 0xff;
158 }
159 return n;
160 }
161
BN_bn2le_padded(uint8_t * out,size_t len,const BIGNUM * in)162 int BN_bn2le_padded(uint8_t *out, size_t len, const BIGNUM *in) {
163 /* If we don't have enough space, fail out. */
164 size_t num_bytes = BN_num_bytes(in);
165 if (len < num_bytes) {
166 return 0;
167 }
168
169 /* We only support little-endian platforms, so we can simply memcpy into the
170 * internal representation. */
171 OPENSSL_memcpy(out, in->d, num_bytes);
172
173 /* Pad out the rest of the buffer with zeroes. */
174 OPENSSL_memset(out + num_bytes, 0, len - num_bytes);
175
176 return 1;
177 }
178
179 /* constant_time_select_ulong returns |x| if |v| is 1 and |y| if |v| is 0. Its
180 * behavior is undefined if |v| takes any other value. */
constant_time_select_ulong(int v,BN_ULONG x,BN_ULONG y)181 static BN_ULONG constant_time_select_ulong(int v, BN_ULONG x, BN_ULONG y) {
182 BN_ULONG mask = v;
183 mask--;
184
185 return (~mask & x) | (mask & y);
186 }
187
188 /* constant_time_le_size_t returns 1 if |x| <= |y| and 0 otherwise. |x| and |y|
189 * must not have their MSBs set. */
constant_time_le_size_t(size_t x,size_t y)190 static int constant_time_le_size_t(size_t x, size_t y) {
191 return ((x - y - 1) >> (sizeof(size_t) * 8 - 1)) & 1;
192 }
193
194 /* read_word_padded returns the |i|'th word of |in|, if it is not out of
195 * bounds. Otherwise, it returns 0. It does so without branches on the size of
196 * |in|, however it necessarily does not have the same memory access pattern. If
197 * the access would be out of bounds, it reads the last word of |in|. |in| must
198 * not be zero. */
read_word_padded(const BIGNUM * in,size_t i)199 static BN_ULONG read_word_padded(const BIGNUM *in, size_t i) {
200 /* Read |in->d[i]| if valid. Otherwise, read the last word. */
201 BN_ULONG l = in->d[constant_time_select_ulong(
202 constant_time_le_size_t(in->dmax, i), in->dmax - 1, i)];
203
204 /* Clamp to zero if above |d->top|. */
205 return constant_time_select_ulong(constant_time_le_size_t(in->top, i), 0, l);
206 }
207
BN_bn2bin_padded(uint8_t * out,size_t len,const BIGNUM * in)208 int BN_bn2bin_padded(uint8_t *out, size_t len, const BIGNUM *in) {
209 /* Special case for |in| = 0. Just branch as the probability is negligible. */
210 if (BN_is_zero(in)) {
211 OPENSSL_memset(out, 0, len);
212 return 1;
213 }
214
215 /* Check if the integer is too big. This case can exit early in non-constant
216 * time. */
217 if ((size_t)in->top > (len + (BN_BYTES - 1)) / BN_BYTES) {
218 return 0;
219 }
220 if ((len % BN_BYTES) != 0) {
221 BN_ULONG l = read_word_padded(in, len / BN_BYTES);
222 if (l >> (8 * (len % BN_BYTES)) != 0) {
223 return 0;
224 }
225 }
226
227 /* Write the bytes out one by one. Serialization is done without branching on
228 * the bits of |in| or on |in->top|, but if the routine would otherwise read
229 * out of bounds, the memory access pattern can't be fixed. However, for an
230 * RSA key of size a multiple of the word size, the probability of BN_BYTES
231 * leading zero octets is low.
232 *
233 * See Falko Stenzke, "Manger's Attack revisited", ICICS 2010. */
234 size_t i = len;
235 while (i--) {
236 BN_ULONG l = read_word_padded(in, i / BN_BYTES);
237 *(out++) = (uint8_t)(l >> (8 * (i % BN_BYTES))) & 0xff;
238 }
239 return 1;
240 }
241
BN_get_word(const BIGNUM * bn)242 BN_ULONG BN_get_word(const BIGNUM *bn) {
243 switch (bn->top) {
244 case 0:
245 return 0;
246 case 1:
247 return bn->d[0];
248 default:
249 return BN_MASK2;
250 }
251 }
252
BN_get_u64(const BIGNUM * bn,uint64_t * out)253 int BN_get_u64(const BIGNUM *bn, uint64_t *out) {
254 switch (bn->top) {
255 case 0:
256 *out = 0;
257 return 1;
258 case 1:
259 *out = bn->d[0];
260 return 1;
261 #if defined(OPENSSL_32_BIT)
262 case 2:
263 *out = (uint64_t) bn->d[0] | (((uint64_t) bn->d[1]) << 32);
264 return 1;
265 #endif
266 default:
267 return 0;
268 }
269 }
270