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
65BIGNUM *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
114BIGNUM *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
150size_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.
168static 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.
177static 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.
186static 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
199static 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
211int 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
232int 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
254BN_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
265int 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