1// Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.
2//
3// Licensed under the Apache License, Version 2.0 (the "License");
4// you may not use this file except in compliance with the License.
5// You may obtain a copy of the License at
6//
7//     https://www.apache.org/licenses/LICENSE-2.0
8//
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS IS" BASIS,
11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12// See the License for the specific language governing permissions and
13// limitations under the License.
14
15#include <openssl/bn.h>
16
17#include <assert.h>
18#include <limits.h>
19
20#include "internal.h"
21
22void bn_big_endian_to_words(BN_ULONG *out, size_t out_len, const uint8_t *in,
23                            size_t in_len) {
24  // The caller should have sized |out| to fit |in| without truncating. This
25  // condition ensures we do not overflow |out|, so use a runtime check.
26  BSSL_CHECK(in_len <= out_len * sizeof(BN_ULONG));
27
28  // Load whole words.
29  while (in_len >= sizeof(BN_ULONG)) {
30    in_len -= sizeof(BN_ULONG);
31    out[0] = CRYPTO_load_word_be(in + in_len);
32    out++;
33    out_len--;
34  }
35
36  // Load the last partial word.
37  if (in_len != 0) {
38    BN_ULONG word = 0;
39    for (size_t i = 0; i < in_len; i++) {
40      word = (word << 8) | in[i];
41    }
42    out[0] = word;
43    out++;
44    out_len--;
45  }
46
47  // Fill the remainder with zeros.
48  OPENSSL_memset(out, 0, out_len * sizeof(BN_ULONG));
49}
50
51BIGNUM *BN_bin2bn(const uint8_t *in, size_t len, BIGNUM *ret) {
52  BIGNUM *bn = NULL;
53  if (ret == NULL) {
54    bn = BN_new();
55    if (bn == NULL) {
56      return NULL;
57    }
58    ret = bn;
59  }
60
61  if (len == 0) {
62    ret->width = 0;
63    return ret;
64  }
65
66  size_t num_words = ((len - 1) / BN_BYTES) + 1;
67  if (!bn_wexpand(ret, num_words)) {
68    BN_free(bn);
69    return NULL;
70  }
71
72  // |bn_wexpand| must check bounds on |num_words| to write it into
73  // |ret->dmax|.
74  assert(num_words <= INT_MAX);
75  ret->width = (int)num_words;
76  ret->neg = 0;
77
78  bn_big_endian_to_words(ret->d, ret->width, in, len);
79  return ret;
80}
81
82BIGNUM *BN_lebin2bn(const uint8_t *in, size_t len, BIGNUM *ret) {
83  BIGNUM *bn = NULL;
84  if (ret == NULL) {
85    bn = BN_new();
86    if (bn == NULL) {
87      return NULL;
88    }
89    ret = bn;
90  }
91
92  if (len == 0) {
93    ret->width = 0;
94    ret->neg = 0;
95    return ret;
96  }
97
98  // Reserve enough space in |ret|.
99  size_t num_words = ((len - 1) / BN_BYTES) + 1;
100  if (!bn_wexpand(ret, num_words)) {
101    BN_free(bn);
102    return NULL;
103  }
104  ret->width = (int)num_words;
105
106  // Make sure the top bytes will be zeroed.
107  ret->d[num_words - 1] = 0;
108
109  // We only support little-endian platforms, so we can simply memcpy the
110  // internal representation.
111  OPENSSL_memcpy(ret->d, in, len);
112  return ret;
113}
114
115BIGNUM *BN_le2bn(const uint8_t *in, size_t len, BIGNUM *ret) {
116  return BN_lebin2bn(in, len, ret);
117}
118
119// fits_in_bytes returns one if the |num_words| words in |words| can be
120// represented in |num_bytes| bytes.
121static int fits_in_bytes(const BN_ULONG *words, size_t num_words,
122                         size_t num_bytes) {
123  const uint8_t *bytes = (const uint8_t *)words;
124  size_t tot_bytes = num_words * sizeof(BN_ULONG);
125  uint8_t mask = 0;
126  for (size_t i = num_bytes; i < tot_bytes; i++) {
127    mask |= bytes[i];
128  }
129  return mask == 0;
130}
131
132void bn_assert_fits_in_bytes(const BIGNUM *bn, size_t num) {
133  const uint8_t *bytes = (const uint8_t *)bn->d;
134  size_t tot_bytes = bn->width * sizeof(BN_ULONG);
135  if (tot_bytes > num) {
136    CONSTTIME_DECLASSIFY(bytes + num, tot_bytes - num);
137    for (size_t i = num; i < tot_bytes; i++) {
138      assert(bytes[i] == 0);
139    }
140    (void)bytes;
141  }
142}
143
144void bn_words_to_big_endian(uint8_t *out, size_t out_len, const BN_ULONG *in,
145                            size_t in_len) {
146  // The caller should have selected an output length without truncation.
147  declassify_assert(fits_in_bytes(in, in_len, out_len));
148
149  // We only support little-endian platforms, so the internal representation is
150  // also little-endian as bytes. We can simply copy it in reverse.
151  const uint8_t *bytes = (const uint8_t *)in;
152  size_t num_bytes = in_len * sizeof(BN_ULONG);
153  if (out_len < num_bytes) {
154    num_bytes = out_len;
155  }
156
157  for (size_t i = 0; i < num_bytes; i++) {
158    out[out_len - i - 1] = bytes[i];
159  }
160  // Pad out the rest of the buffer with zeroes.
161  OPENSSL_memset(out, 0, out_len - num_bytes);
162}
163
164size_t BN_bn2bin(const BIGNUM *in, uint8_t *out) {
165  size_t n = BN_num_bytes(in);
166  bn_words_to_big_endian(out, n, in->d, in->width);
167  return n;
168}
169
170int BN_bn2le_padded(uint8_t *out, size_t len, const BIGNUM *in) {
171  if (!fits_in_bytes(in->d, in->width, len)) {
172    return 0;
173  }
174
175  // We only support little-endian platforms, so we can simply memcpy into the
176  // internal representation.
177  const uint8_t *bytes = (const uint8_t *)in->d;
178  size_t num_bytes = in->width * BN_BYTES;
179  if (len < num_bytes) {
180    num_bytes = len;
181  }
182
183  OPENSSL_memcpy(out, bytes, num_bytes);
184  // Pad out the rest of the buffer with zeroes.
185  OPENSSL_memset(out + num_bytes, 0, len - num_bytes);
186  return 1;
187}
188
189int BN_bn2bin_padded(uint8_t *out, size_t len, const BIGNUM *in) {
190  if (!fits_in_bytes(in->d, in->width, len)) {
191    return 0;
192  }
193
194  bn_words_to_big_endian(out, len, in->d, in->width);
195  return 1;
196}
197
198BN_ULONG BN_get_word(const BIGNUM *bn) {
199  switch (bn_minimal_width(bn)) {
200    case 0:
201      return 0;
202    case 1:
203      return bn->d[0];
204    default:
205      return BN_MASK2;
206  }
207}
208
209int BN_get_u64(const BIGNUM *bn, uint64_t *out) {
210  switch (bn_minimal_width(bn)) {
211    case 0:
212      *out = 0;
213      return 1;
214    case 1:
215      *out = bn->d[0];
216      return 1;
217#if defined(OPENSSL_32_BIT)
218    case 2:
219      *out = (uint64_t) bn->d[0] | (((uint64_t) bn->d[1]) << 32);
220      return 1;
221#endif
222    default:
223      return 0;
224  }
225}
226