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