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
162 // TODO(davidben): This does not need to be quite so complex once the |BIGNUM|s
163 // we care about are fixed-width. |read_word_padded| is a hack to paper over
164 // parts of the |bn_correct_top| leak. Fix that, and this can be simpler.
165
166 // constant_time_select_ulong returns |x| if |v| is 1 and |y| if |v| is 0. Its
167 // behavior is undefined if |v| takes any other value.
constant_time_select_ulong(int v,BN_ULONG x,BN_ULONG y)168 static BN_ULONG constant_time_select_ulong(int v, BN_ULONG x, BN_ULONG y) {
169 BN_ULONG mask = v;
170 mask--;
171
172 return (~mask & x) | (mask & y);
173 }
174
175 // constant_time_le_size_t returns 1 if |x| <= |y| and 0 otherwise. |x| and |y|
176 // must not have their MSBs set.
constant_time_le_size_t(size_t x,size_t y)177 static int constant_time_le_size_t(size_t x, size_t y) {
178 return ((x - y - 1) >> (sizeof(size_t) * 8 - 1)) & 1;
179 }
180
181 // read_word_padded returns the |i|'th word of |in|, if it is not out of
182 // bounds. Otherwise, it returns 0. It does so without branches on the size of
183 // |in|, however it necessarily does not have the same memory access pattern. If
184 // the access would be out of bounds, it reads the last word of |in|. |in| must
185 // not be zero.
read_word_padded(const BIGNUM * in,size_t i)186 static BN_ULONG read_word_padded(const BIGNUM *in, size_t i) {
187 if (in->dmax == 0) {
188 return 0;
189 }
190
191 // Read |in->d[i]| if valid. Otherwise, read the last word.
192 BN_ULONG l = in->d[constant_time_select_ulong(
193 constant_time_le_size_t(in->dmax, i), in->dmax - 1, i)];
194
195 // Clamp to zero if above |d->top|.
196 return constant_time_select_ulong(constant_time_le_size_t(in->top, i), 0, l);
197 }
198
fits_in_bytes(const BIGNUM * in,size_t len)199 static int fits_in_bytes(const BIGNUM *in, size_t len) {
200 BN_ULONG mask = 0;
201 for (size_t i = (len + (BN_BYTES - 1)) / BN_BYTES; i < (size_t)in->top; i++) {
202 mask |= in->d[i];
203 }
204 if ((len % BN_BYTES) != 0) {
205 BN_ULONG l = read_word_padded(in, len / BN_BYTES);
206 mask |= l >> (8 * (len % BN_BYTES));
207 }
208 return mask == 0;
209 }
210
BN_bn2le_padded(uint8_t * out,size_t len,const BIGNUM * in)211 int BN_bn2le_padded(uint8_t *out, size_t len, const BIGNUM *in) {
212 // If we don't have enough space, fail out.
213 if (!fits_in_bytes(in, len)) {
214 return 0;
215 }
216
217 size_t todo = in->top * BN_BYTES;
218 if (todo > len) {
219 todo = len;
220 }
221
222 // We only support little-endian platforms, so we can simply memcpy into the
223 // internal representation.
224 OPENSSL_memcpy(out, in->d, todo);
225
226 // Pad out the rest of the buffer with zeroes.
227 OPENSSL_memset(out + todo, 0, len - todo);
228
229 return 1;
230 }
231
BN_bn2bin_padded(uint8_t * out,size_t len,const BIGNUM * in)232 int BN_bn2bin_padded(uint8_t *out, size_t len, const BIGNUM *in) {
233 // Check if the integer is too big. This case can exit early in non-constant
234 // time.
235 if (!fits_in_bytes(in, len)) {
236 return 0;
237 }
238
239 // Write the bytes out one by one. Serialization is done without branching on
240 // the bits of |in| or on |in->top|, but if the routine would otherwise read
241 // out of bounds, the memory access pattern can't be fixed. However, for an
242 // RSA key of size a multiple of the word size, the probability of BN_BYTES
243 // leading zero octets is low.
244 //
245 // See Falko Stenzke, "Manger's Attack revisited", ICICS 2010.
246 size_t i = len;
247 while (i--) {
248 BN_ULONG l = read_word_padded(in, i / BN_BYTES);
249 *(out++) = (uint8_t)(l >> (8 * (i % BN_BYTES))) & 0xff;
250 }
251 return 1;
252 }
253
BN_get_word(const BIGNUM * bn)254 BN_ULONG BN_get_word(const BIGNUM *bn) {
255 switch (bn_minimal_width(bn)) {
256 case 0:
257 return 0;
258 case 1:
259 return bn->d[0];
260 default:
261 return BN_MASK2;
262 }
263 }
264
BN_get_u64(const BIGNUM * bn,uint64_t * out)265 int BN_get_u64(const BIGNUM *bn, uint64_t *out) {
266 switch (bn_minimal_width(bn)) {
267 case 0:
268 *out = 0;
269 return 1;
270 case 1:
271 *out = bn->d[0];
272 return 1;
273 #if defined(OPENSSL_32_BIT)
274 case 2:
275 *out = (uint64_t) bn->d[0] | (((uint64_t) bn->d[1]) << 32);
276 return 1;
277 #endif
278 default:
279 return 0;
280 }
281 }
282