1 /* ====================================================================
2 * Copyright (c) 2012 The OpenSSL Project. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 *
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 *
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in
13 * the documentation and/or other materials provided with the
14 * distribution.
15 *
16 * 3. All advertising materials mentioning features or use of this
17 * software must display the following acknowledgment:
18 * "This product includes software developed by the OpenSSL Project
19 * for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
20 *
21 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
22 * endorse or promote products derived from this software without
23 * prior written permission. For written permission, please contact
24 * openssl-core@openssl.org.
25 *
26 * 5. Products derived from this software may not be called "OpenSSL"
27 * nor may "OpenSSL" appear in their names without prior written
28 * permission of the OpenSSL Project.
29 *
30 * 6. Redistributions of any form whatsoever must retain the following
31 * acknowledgment:
32 * "This product includes software developed by the OpenSSL Project
33 * for use in the OpenSSL Toolkit (http://www.openssl.org/)"
34 *
35 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
36 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
37 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
38 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR
39 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
40 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
41 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
42 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
43 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
44 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
45 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
46 * OF THE POSSIBILITY OF SUCH DAMAGE.
47 * ====================================================================
48 *
49 * This product includes cryptographic software written by Eric Young
50 * (eay@cryptsoft.com). This product includes software written by Tim
51 * Hudson (tjh@cryptsoft.com). */
52
53 #include <assert.h>
54 #include <string.h>
55
56 #include <openssl/digest.h>
57 #include <openssl/obj.h>
58 #include <openssl/sha.h>
59
60 #include "../internal.h"
61
62
63 /* TODO(davidben): unsigned should be size_t. The various constant_time
64 * functions need to be switched to size_t. */
65
66 /* MAX_HASH_BIT_COUNT_BYTES is the maximum number of bytes in the hash's length
67 * field. (SHA-384/512 have 128-bit length.) */
68 #define MAX_HASH_BIT_COUNT_BYTES 16
69
70 /* MAX_HASH_BLOCK_SIZE is the maximum hash block size that we'll support.
71 * Currently SHA-384/512 has a 128-byte block size and that's the largest
72 * supported by TLS.) */
73 #define MAX_HASH_BLOCK_SIZE 128
74
EVP_tls_cbc_remove_padding(unsigned * out_len,const uint8_t * in,unsigned in_len,unsigned block_size,unsigned mac_size)75 int EVP_tls_cbc_remove_padding(unsigned *out_len,
76 const uint8_t *in, unsigned in_len,
77 unsigned block_size, unsigned mac_size) {
78 unsigned padding_length, good, to_check, i;
79 const unsigned overhead = 1 /* padding length byte */ + mac_size;
80
81 /* These lengths are all public so we can test them in non-constant time. */
82 if (overhead > in_len) {
83 return 0;
84 }
85
86 padding_length = in[in_len - 1];
87
88 good = constant_time_ge(in_len, overhead + padding_length);
89 /* The padding consists of a length byte at the end of the record and
90 * then that many bytes of padding, all with the same value as the
91 * length byte. Thus, with the length byte included, there are i+1
92 * bytes of padding.
93 *
94 * We can't check just |padding_length+1| bytes because that leaks
95 * decrypted information. Therefore we always have to check the maximum
96 * amount of padding possible. (Again, the length of the record is
97 * public information so we can use it.) */
98 to_check = 256; /* maximum amount of padding, inc length byte. */
99 if (to_check > in_len) {
100 to_check = in_len;
101 }
102
103 for (i = 0; i < to_check; i++) {
104 uint8_t mask = constant_time_ge_8(padding_length, i);
105 uint8_t b = in[in_len - 1 - i];
106 /* The final |padding_length+1| bytes should all have the value
107 * |padding_length|. Therefore the XOR should be zero. */
108 good &= ~(mask & (padding_length ^ b));
109 }
110
111 /* If any of the final |padding_length+1| bytes had the wrong value,
112 * one or more of the lower eight bits of |good| will be cleared. */
113 good = constant_time_eq(0xff, good & 0xff);
114
115 /* Always treat |padding_length| as zero on error. If, assuming block size of
116 * 16, a padding of [<15 arbitrary bytes> 15] treated |padding_length| as 16
117 * and returned -1, distinguishing good MAC and bad padding from bad MAC and
118 * bad padding would give POODLE's padding oracle. */
119 padding_length = good & (padding_length + 1);
120 *out_len = in_len - padding_length;
121
122 return constant_time_select_int(good, 1, -1);
123 }
124
125 /* If CBC_MAC_ROTATE_IN_PLACE is defined then EVP_tls_cbc_copy_mac is performed
126 * with variable accesses in a 64-byte-aligned buffer. Assuming that this fits
127 * into a single or pair of cache-lines, then the variable memory accesses don't
128 * actually affect the timing. CPUs with smaller cache-lines [if any] are not
129 * multi-core and are not considered vulnerable to cache-timing attacks. */
130 #define CBC_MAC_ROTATE_IN_PLACE
131
EVP_tls_cbc_copy_mac(uint8_t * out,unsigned md_size,const uint8_t * in,unsigned in_len,unsigned orig_len)132 void EVP_tls_cbc_copy_mac(uint8_t *out, unsigned md_size,
133 const uint8_t *in, unsigned in_len,
134 unsigned orig_len) {
135 #if defined(CBC_MAC_ROTATE_IN_PLACE)
136 uint8_t rotated_mac_buf[64 + EVP_MAX_MD_SIZE];
137 uint8_t *rotated_mac;
138 #else
139 uint8_t rotated_mac[EVP_MAX_MD_SIZE];
140 #endif
141
142 /* mac_end is the index of |in| just after the end of the MAC. */
143 unsigned mac_end = in_len;
144 unsigned mac_start = mac_end - md_size;
145 /* scan_start contains the number of bytes that we can ignore because
146 * the MAC's position can only vary by 255 bytes. */
147 unsigned scan_start = 0;
148 unsigned i, j;
149 unsigned div_spoiler;
150 unsigned rotate_offset;
151
152 assert(orig_len >= in_len);
153 assert(in_len >= md_size);
154 assert(md_size <= EVP_MAX_MD_SIZE);
155
156 #if defined(CBC_MAC_ROTATE_IN_PLACE)
157 rotated_mac = rotated_mac_buf + ((0 - (size_t)rotated_mac_buf) & 63);
158 #endif
159
160 /* This information is public so it's safe to branch based on it. */
161 if (orig_len > md_size + 255 + 1) {
162 scan_start = orig_len - (md_size + 255 + 1);
163 }
164 /* div_spoiler contains a multiple of md_size that is used to cause the
165 * modulo operation to be constant time. Without this, the time varies
166 * based on the amount of padding when running on Intel chips at least.
167 *
168 * The aim of right-shifting md_size is so that the compiler doesn't
169 * figure out that it can remove div_spoiler as that would require it
170 * to prove that md_size is always even, which I hope is beyond it. */
171 div_spoiler = md_size >> 1;
172 div_spoiler <<= (sizeof(div_spoiler) - 1) * 8;
173 rotate_offset = (div_spoiler + mac_start - scan_start) % md_size;
174
175 memset(rotated_mac, 0, md_size);
176 for (i = scan_start, j = 0; i < orig_len; i++) {
177 uint8_t mac_started = constant_time_ge_8(i, mac_start);
178 uint8_t mac_ended = constant_time_ge_8(i, mac_end);
179 uint8_t b = in[i];
180 rotated_mac[j++] |= b & mac_started & ~mac_ended;
181 j &= constant_time_lt(j, md_size);
182 }
183
184 /* Now rotate the MAC */
185 #if defined(CBC_MAC_ROTATE_IN_PLACE)
186 j = 0;
187 for (i = 0; i < md_size; i++) {
188 /* in case cache-line is 32 bytes, touch second line */
189 ((volatile uint8_t *)rotated_mac)[rotate_offset ^ 32];
190 out[j++] = rotated_mac[rotate_offset++];
191 rotate_offset &= constant_time_lt(rotate_offset, md_size);
192 }
193 #else
194 memset(out, 0, md_size);
195 rotate_offset = md_size - rotate_offset;
196 rotate_offset &= constant_time_lt(rotate_offset, md_size);
197 for (i = 0; i < md_size; i++) {
198 for (j = 0; j < md_size; j++) {
199 out[j] |= rotated_mac[i] & constant_time_eq_8(j, rotate_offset);
200 }
201 rotate_offset++;
202 rotate_offset &= constant_time_lt(rotate_offset, md_size);
203 }
204 #endif
205 }
206
207 /* u32toBE serialises an unsigned, 32-bit number (n) as four bytes at (p) in
208 * big-endian order. The value of p is advanced by four. */
209 #define u32toBE(n, p) \
210 (*((p)++)=(uint8_t)(n>>24), \
211 *((p)++)=(uint8_t)(n>>16), \
212 *((p)++)=(uint8_t)(n>>8), \
213 *((p)++)=(uint8_t)(n))
214
215 /* u64toBE serialises an unsigned, 64-bit number (n) as eight bytes at (p) in
216 * big-endian order. The value of p is advanced by eight. */
217 #define u64toBE(n, p) \
218 (*((p)++)=(uint8_t)(n>>56), \
219 *((p)++)=(uint8_t)(n>>48), \
220 *((p)++)=(uint8_t)(n>>40), \
221 *((p)++)=(uint8_t)(n>>32), \
222 *((p)++)=(uint8_t)(n>>24), \
223 *((p)++)=(uint8_t)(n>>16), \
224 *((p)++)=(uint8_t)(n>>8), \
225 *((p)++)=(uint8_t)(n))
226
227 /* These functions serialize the state of a hash and thus perform the standard
228 * "final" operation without adding the padding and length that such a function
229 * typically does. */
tls1_sha1_final_raw(void * ctx,uint8_t * md_out)230 static void tls1_sha1_final_raw(void *ctx, uint8_t *md_out) {
231 SHA_CTX *sha1 = ctx;
232 u32toBE(sha1->h[0], md_out);
233 u32toBE(sha1->h[1], md_out);
234 u32toBE(sha1->h[2], md_out);
235 u32toBE(sha1->h[3], md_out);
236 u32toBE(sha1->h[4], md_out);
237 }
238 #define LARGEST_DIGEST_CTX SHA_CTX
239
tls1_sha256_final_raw(void * ctx,uint8_t * md_out)240 static void tls1_sha256_final_raw(void *ctx, uint8_t *md_out) {
241 SHA256_CTX *sha256 = ctx;
242 unsigned i;
243
244 for (i = 0; i < 8; i++) {
245 u32toBE(sha256->h[i], md_out);
246 }
247 }
248 #undef LARGEST_DIGEST_CTX
249 #define LARGEST_DIGEST_CTX SHA256_CTX
250
tls1_sha512_final_raw(void * ctx,uint8_t * md_out)251 static void tls1_sha512_final_raw(void *ctx, uint8_t *md_out) {
252 SHA512_CTX *sha512 = ctx;
253 unsigned i;
254
255 for (i = 0; i < 8; i++) {
256 u64toBE(sha512->h[i], md_out);
257 }
258 }
259 #undef LARGEST_DIGEST_CTX
260 #define LARGEST_DIGEST_CTX SHA512_CTX
261
EVP_tls_cbc_record_digest_supported(const EVP_MD * md)262 int EVP_tls_cbc_record_digest_supported(const EVP_MD *md) {
263 switch (EVP_MD_type(md)) {
264 case NID_sha1:
265 case NID_sha256:
266 case NID_sha384:
267 return 1;
268
269 default:
270 return 0;
271 }
272 }
273
EVP_tls_cbc_digest_record(const EVP_MD * md,uint8_t * md_out,size_t * md_out_size,const uint8_t header[13],const uint8_t * data,size_t data_plus_mac_size,size_t data_plus_mac_plus_padding_size,const uint8_t * mac_secret,unsigned mac_secret_length)274 int EVP_tls_cbc_digest_record(const EVP_MD *md, uint8_t *md_out,
275 size_t *md_out_size, const uint8_t header[13],
276 const uint8_t *data, size_t data_plus_mac_size,
277 size_t data_plus_mac_plus_padding_size,
278 const uint8_t *mac_secret,
279 unsigned mac_secret_length) {
280 union {
281 double align;
282 uint8_t c[sizeof(LARGEST_DIGEST_CTX)];
283 } md_state;
284 void (*md_final_raw)(void *ctx, uint8_t *md_out);
285 void (*md_transform)(void *ctx, const uint8_t *block);
286 unsigned md_size, md_block_size = 64;
287 unsigned len, max_mac_bytes, num_blocks, num_starting_blocks, k,
288 mac_end_offset, c, index_a, index_b;
289 unsigned int bits; /* at most 18 bits */
290 uint8_t length_bytes[MAX_HASH_BIT_COUNT_BYTES];
291 /* hmac_pad is the masked HMAC key. */
292 uint8_t hmac_pad[MAX_HASH_BLOCK_SIZE];
293 uint8_t first_block[MAX_HASH_BLOCK_SIZE];
294 uint8_t mac_out[EVP_MAX_MD_SIZE];
295 unsigned i, j, md_out_size_u;
296 EVP_MD_CTX md_ctx;
297 /* mdLengthSize is the number of bytes in the length field that terminates
298 * the hash. */
299 unsigned md_length_size = 8;
300
301 /* This is a, hopefully redundant, check that allows us to forget about
302 * many possible overflows later in this function. */
303 assert(data_plus_mac_plus_padding_size < 1024 * 1024);
304
305 switch (EVP_MD_type(md)) {
306 case NID_sha1:
307 SHA1_Init((SHA_CTX *)md_state.c);
308 md_final_raw = tls1_sha1_final_raw;
309 md_transform =
310 (void (*)(void *ctx, const uint8_t *block))SHA1_Transform;
311 md_size = 20;
312 break;
313
314 case NID_sha256:
315 SHA256_Init((SHA256_CTX *)md_state.c);
316 md_final_raw = tls1_sha256_final_raw;
317 md_transform =
318 (void (*)(void *ctx, const uint8_t *block))SHA256_Transform;
319 md_size = 32;
320 break;
321
322 case NID_sha384:
323 SHA384_Init((SHA512_CTX *)md_state.c);
324 md_final_raw = tls1_sha512_final_raw;
325 md_transform =
326 (void (*)(void *ctx, const uint8_t *block))SHA512_Transform;
327 md_size = 384 / 8;
328 md_block_size = 128;
329 md_length_size = 16;
330 break;
331
332 default:
333 /* EVP_tls_cbc_record_digest_supported should have been called first to
334 * check that the hash function is supported. */
335 assert(0);
336 *md_out_size = 0;
337 return 0;
338 }
339
340 assert(md_length_size <= MAX_HASH_BIT_COUNT_BYTES);
341 assert(md_block_size <= MAX_HASH_BLOCK_SIZE);
342 assert(md_size <= EVP_MAX_MD_SIZE);
343
344 static const unsigned kHeaderLength = 13;
345
346 /* kVarianceBlocks is the number of blocks of the hash that we have to
347 * calculate in constant time because they could be altered by the
348 * padding value.
349 *
350 * TLSv1 has MACs up to 48 bytes long (SHA-384) and the padding is not
351 * required to be minimal. Therefore we say that the final six blocks
352 * can vary based on the padding. */
353 static const unsigned kVarianceBlocks = 6;
354
355 /* From now on we're dealing with the MAC, which conceptually has 13
356 * bytes of `header' before the start of the data. */
357 len = data_plus_mac_plus_padding_size + kHeaderLength;
358 /* max_mac_bytes contains the maximum bytes of bytes in the MAC, including
359 * |header|, assuming that there's no padding. */
360 max_mac_bytes = len - md_size - 1;
361 /* num_blocks is the maximum number of hash blocks. */
362 num_blocks =
363 (max_mac_bytes + 1 + md_length_size + md_block_size - 1) / md_block_size;
364 /* In order to calculate the MAC in constant time we have to handle
365 * the final blocks specially because the padding value could cause the
366 * end to appear somewhere in the final |kVarianceBlocks| blocks and we
367 * can't leak where. However, |num_starting_blocks| worth of data can
368 * be hashed right away because no padding value can affect whether
369 * they are plaintext. */
370 num_starting_blocks = 0;
371 /* k is the starting byte offset into the conceptual header||data where
372 * we start processing. */
373 k = 0;
374 /* mac_end_offset is the index just past the end of the data to be
375 * MACed. */
376 mac_end_offset = data_plus_mac_size + kHeaderLength - md_size;
377 /* c is the index of the 0x80 byte in the final hash block that
378 * contains application data. */
379 c = mac_end_offset % md_block_size;
380 /* index_a is the hash block number that contains the 0x80 terminating
381 * value. */
382 index_a = mac_end_offset / md_block_size;
383 /* index_b is the hash block number that contains the 64-bit hash
384 * length, in bits. */
385 index_b = (mac_end_offset + md_length_size) / md_block_size;
386 /* bits is the hash-length in bits. It includes the additional hash
387 * block for the masked HMAC key. */
388
389 if (num_blocks > kVarianceBlocks) {
390 num_starting_blocks = num_blocks - kVarianceBlocks;
391 k = md_block_size * num_starting_blocks;
392 }
393
394 bits = 8 * mac_end_offset;
395
396 /* Compute the initial HMAC block. */
397 bits += 8 * md_block_size;
398 memset(hmac_pad, 0, md_block_size);
399 assert(mac_secret_length <= sizeof(hmac_pad));
400 memcpy(hmac_pad, mac_secret, mac_secret_length);
401 for (i = 0; i < md_block_size; i++) {
402 hmac_pad[i] ^= 0x36;
403 }
404
405 md_transform(md_state.c, hmac_pad);
406
407 memset(length_bytes, 0, md_length_size - 4);
408 length_bytes[md_length_size - 4] = (uint8_t)(bits >> 24);
409 length_bytes[md_length_size - 3] = (uint8_t)(bits >> 16);
410 length_bytes[md_length_size - 2] = (uint8_t)(bits >> 8);
411 length_bytes[md_length_size - 1] = (uint8_t)bits;
412
413 if (k > 0) {
414 /* k is a multiple of md_block_size. */
415 memcpy(first_block, header, 13);
416 memcpy(first_block + 13, data, md_block_size - 13);
417 md_transform(md_state.c, first_block);
418 for (i = 1; i < k / md_block_size; i++) {
419 md_transform(md_state.c, data + md_block_size * i - 13);
420 }
421 }
422
423 memset(mac_out, 0, sizeof(mac_out));
424
425 /* We now process the final hash blocks. For each block, we construct
426 * it in constant time. If the |i==index_a| then we'll include the 0x80
427 * bytes and zero pad etc. For each block we selectively copy it, in
428 * constant time, to |mac_out|. */
429 for (i = num_starting_blocks; i <= num_starting_blocks + kVarianceBlocks;
430 i++) {
431 uint8_t block[MAX_HASH_BLOCK_SIZE];
432 uint8_t is_block_a = constant_time_eq_8(i, index_a);
433 uint8_t is_block_b = constant_time_eq_8(i, index_b);
434 for (j = 0; j < md_block_size; j++) {
435 uint8_t b = 0, is_past_c, is_past_cp1;
436 if (k < kHeaderLength) {
437 b = header[k];
438 } else if (k < data_plus_mac_plus_padding_size + kHeaderLength) {
439 b = data[k - kHeaderLength];
440 }
441 k++;
442
443 is_past_c = is_block_a & constant_time_ge_8(j, c);
444 is_past_cp1 = is_block_a & constant_time_ge_8(j, c + 1);
445 /* If this is the block containing the end of the
446 * application data, and we are at the offset for the
447 * 0x80 value, then overwrite b with 0x80. */
448 b = constant_time_select_8(is_past_c, 0x80, b);
449 /* If this the the block containing the end of the
450 * application data and we're past the 0x80 value then
451 * just write zero. */
452 b = b & ~is_past_cp1;
453 /* If this is index_b (the final block), but not
454 * index_a (the end of the data), then the 64-bit
455 * length didn't fit into index_a and we're having to
456 * add an extra block of zeros. */
457 b &= ~is_block_b | is_block_a;
458
459 /* The final bytes of one of the blocks contains the
460 * length. */
461 if (j >= md_block_size - md_length_size) {
462 /* If this is index_b, write a length byte. */
463 b = constant_time_select_8(
464 is_block_b, length_bytes[j - (md_block_size - md_length_size)], b);
465 }
466 block[j] = b;
467 }
468
469 md_transform(md_state.c, block);
470 md_final_raw(md_state.c, block);
471 /* If this is index_b, copy the hash value to |mac_out|. */
472 for (j = 0; j < md_size; j++) {
473 mac_out[j] |= block[j] & is_block_b;
474 }
475 }
476
477 EVP_MD_CTX_init(&md_ctx);
478 if (!EVP_DigestInit_ex(&md_ctx, md, NULL /* engine */)) {
479 EVP_MD_CTX_cleanup(&md_ctx);
480 return 0;
481 }
482
483 /* Complete the HMAC in the standard manner. */
484 for (i = 0; i < md_block_size; i++) {
485 hmac_pad[i] ^= 0x6a;
486 }
487
488 EVP_DigestUpdate(&md_ctx, hmac_pad, md_block_size);
489 EVP_DigestUpdate(&md_ctx, mac_out, md_size);
490 EVP_DigestFinal(&md_ctx, md_out, &md_out_size_u);
491 *md_out_size = md_out_size_u;
492 EVP_MD_CTX_cleanup(&md_ctx);
493
494 return 1;
495 }
496