1 /*
2 * Copyright 2012-2021 The OpenSSL Project Authors. All Rights Reserved.
3 *
4 * Licensed under the OpenSSL license (the "License"). You may not use
5 * this file except in compliance with the License. You can obtain a copy
6 * in the file LICENSE in the source distribution or at
7 * https://www.openssl.org/source/license.html
8 */
9
10 #include "internal/constant_time.h"
11 #include "ssl_local.h"
12 #include "internal/cryptlib.h"
13
14 #include <openssl/md5.h>
15 #include <openssl/sha.h>
16
17 /*
18 * MAX_HASH_BIT_COUNT_BYTES is the maximum number of bytes in the hash's
19 * length field. (SHA-384/512 have 128-bit length.)
20 */
21 #define MAX_HASH_BIT_COUNT_BYTES 16
22
23 /*
24 * MAX_HASH_BLOCK_SIZE is the maximum hash block size that we'll support.
25 * Currently SHA-384/512 has a 128-byte block size and that's the largest
26 * supported by TLS.)
27 */
28 #define MAX_HASH_BLOCK_SIZE 128
29
30 /*
31 * u32toLE serialises an unsigned, 32-bit number (n) as four bytes at (p) in
32 * little-endian order. The value of p is advanced by four.
33 */
34 #define u32toLE(n, p) \
35 (*((p)++)=(unsigned char)(n), \
36 *((p)++)=(unsigned char)(n>>8), \
37 *((p)++)=(unsigned char)(n>>16), \
38 *((p)++)=(unsigned char)(n>>24))
39
40 /*
41 * These functions serialize the state of a hash and thus perform the
42 * standard "final" operation without adding the padding and length that such
43 * a function typically does.
44 */
tls1_md5_final_raw(void * ctx,unsigned char * md_out)45 static void tls1_md5_final_raw(void *ctx, unsigned char *md_out)
46 {
47 MD5_CTX *md5 = ctx;
48 u32toLE(md5->A, md_out);
49 u32toLE(md5->B, md_out);
50 u32toLE(md5->C, md_out);
51 u32toLE(md5->D, md_out);
52 }
53
tls1_sha1_final_raw(void * ctx,unsigned char * md_out)54 static void tls1_sha1_final_raw(void *ctx, unsigned char *md_out)
55 {
56 SHA_CTX *sha1 = ctx;
57 l2n(sha1->h0, md_out);
58 l2n(sha1->h1, md_out);
59 l2n(sha1->h2, md_out);
60 l2n(sha1->h3, md_out);
61 l2n(sha1->h4, md_out);
62 }
63
tls1_sha256_final_raw(void * ctx,unsigned char * md_out)64 static void tls1_sha256_final_raw(void *ctx, unsigned char *md_out)
65 {
66 SHA256_CTX *sha256 = ctx;
67 unsigned i;
68
69 for (i = 0; i < 8; i++) {
70 l2n(sha256->h[i], md_out);
71 }
72 }
73
tls1_sha512_final_raw(void * ctx,unsigned char * md_out)74 static void tls1_sha512_final_raw(void *ctx, unsigned char *md_out)
75 {
76 SHA512_CTX *sha512 = ctx;
77 unsigned i;
78
79 for (i = 0; i < 8; i++) {
80 l2n8(sha512->h[i], md_out);
81 }
82 }
83
84 #undef LARGEST_DIGEST_CTX
85 #define LARGEST_DIGEST_CTX SHA512_CTX
86
87 /*
88 * ssl3_cbc_record_digest_supported returns 1 iff |ctx| uses a hash function
89 * which ssl3_cbc_digest_record supports.
90 */
ssl3_cbc_record_digest_supported(const EVP_MD_CTX * ctx)91 char ssl3_cbc_record_digest_supported(const EVP_MD_CTX *ctx)
92 {
93 switch (EVP_MD_CTX_type(ctx)) {
94 case NID_md5:
95 case NID_sha1:
96 case NID_sha224:
97 case NID_sha256:
98 case NID_sha384:
99 case NID_sha512:
100 return 1;
101 default:
102 return 0;
103 }
104 }
105
106 /*-
107 * ssl3_cbc_digest_record computes the MAC of a decrypted, padded SSLv3/TLS
108 * record.
109 *
110 * ctx: the EVP_MD_CTX from which we take the hash function.
111 * ssl3_cbc_record_digest_supported must return true for this EVP_MD_CTX.
112 * md_out: the digest output. At most EVP_MAX_MD_SIZE bytes will be written.
113 * md_out_size: if non-NULL, the number of output bytes is written here.
114 * header: the 13-byte, TLS record header.
115 * data: the record data itself, less any preceding explicit IV.
116 * data_plus_mac_size: the secret, reported length of the data and MAC
117 * once the padding has been removed.
118 * data_plus_mac_plus_padding_size: the public length of the whole
119 * record, including padding.
120 * is_sslv3: non-zero if we are to use SSLv3. Otherwise, TLS.
121 *
122 * On entry: by virtue of having been through one of the remove_padding
123 * functions, above, we know that data_plus_mac_size is large enough to contain
124 * a padding byte and MAC. (If the padding was invalid, it might contain the
125 * padding too. )
126 * Returns 1 on success or 0 on error
127 */
ssl3_cbc_digest_record(const EVP_MD_CTX * ctx,unsigned char * md_out,size_t * md_out_size,const unsigned char * header,const unsigned char * data,size_t data_plus_mac_size,size_t data_plus_mac_plus_padding_size,const unsigned char * mac_secret,size_t mac_secret_length,char is_sslv3)128 int ssl3_cbc_digest_record(const EVP_MD_CTX *ctx,
129 unsigned char *md_out,
130 size_t *md_out_size,
131 const unsigned char *header,
132 const unsigned char *data,
133 size_t data_plus_mac_size,
134 size_t data_plus_mac_plus_padding_size,
135 const unsigned char *mac_secret,
136 size_t mac_secret_length, char is_sslv3)
137 {
138 union {
139 double align;
140 unsigned char c[sizeof(LARGEST_DIGEST_CTX)];
141 } md_state;
142 void (*md_final_raw) (void *ctx, unsigned char *md_out);
143 void (*md_transform) (void *ctx, const unsigned char *block);
144 size_t md_size, md_block_size = 64;
145 size_t sslv3_pad_length = 40, header_length, variance_blocks,
146 len, max_mac_bytes, num_blocks,
147 num_starting_blocks, k, mac_end_offset, c, index_a, index_b;
148 size_t bits; /* at most 18 bits */
149 unsigned char length_bytes[MAX_HASH_BIT_COUNT_BYTES];
150 /* hmac_pad is the masked HMAC key. */
151 unsigned char hmac_pad[MAX_HASH_BLOCK_SIZE];
152 unsigned char first_block[MAX_HASH_BLOCK_SIZE];
153 unsigned char mac_out[EVP_MAX_MD_SIZE];
154 size_t i, j;
155 unsigned md_out_size_u;
156 EVP_MD_CTX *md_ctx = NULL;
157 /*
158 * mdLengthSize is the number of bytes in the length field that
159 * terminates * the hash.
160 */
161 size_t md_length_size = 8;
162 char length_is_big_endian = 1;
163 int ret;
164
165 /*
166 * This is a, hopefully redundant, check that allows us to forget about
167 * many possible overflows later in this function.
168 */
169 if (!ossl_assert(data_plus_mac_plus_padding_size < 1024 * 1024))
170 return 0;
171
172 switch (EVP_MD_CTX_type(ctx)) {
173 case NID_md5:
174 if (MD5_Init((MD5_CTX *)md_state.c) <= 0)
175 return 0;
176 md_final_raw = tls1_md5_final_raw;
177 md_transform =
178 (void (*)(void *ctx, const unsigned char *block))MD5_Transform;
179 md_size = 16;
180 sslv3_pad_length = 48;
181 length_is_big_endian = 0;
182 break;
183 case NID_sha1:
184 if (SHA1_Init((SHA_CTX *)md_state.c) <= 0)
185 return 0;
186 md_final_raw = tls1_sha1_final_raw;
187 md_transform =
188 (void (*)(void *ctx, const unsigned char *block))SHA1_Transform;
189 md_size = 20;
190 break;
191 case NID_sha224:
192 if (SHA224_Init((SHA256_CTX *)md_state.c) <= 0)
193 return 0;
194 md_final_raw = tls1_sha256_final_raw;
195 md_transform =
196 (void (*)(void *ctx, const unsigned char *block))SHA256_Transform;
197 md_size = 224 / 8;
198 break;
199 case NID_sha256:
200 if (SHA256_Init((SHA256_CTX *)md_state.c) <= 0)
201 return 0;
202 md_final_raw = tls1_sha256_final_raw;
203 md_transform =
204 (void (*)(void *ctx, const unsigned char *block))SHA256_Transform;
205 md_size = 32;
206 break;
207 case NID_sha384:
208 if (SHA384_Init((SHA512_CTX *)md_state.c) <= 0)
209 return 0;
210 md_final_raw = tls1_sha512_final_raw;
211 md_transform =
212 (void (*)(void *ctx, const unsigned char *block))SHA512_Transform;
213 md_size = 384 / 8;
214 md_block_size = 128;
215 md_length_size = 16;
216 break;
217 case NID_sha512:
218 if (SHA512_Init((SHA512_CTX *)md_state.c) <= 0)
219 return 0;
220 md_final_raw = tls1_sha512_final_raw;
221 md_transform =
222 (void (*)(void *ctx, const unsigned char *block))SHA512_Transform;
223 md_size = 64;
224 md_block_size = 128;
225 md_length_size = 16;
226 break;
227 default:
228 /*
229 * ssl3_cbc_record_digest_supported should have been called first to
230 * check that the hash function is supported.
231 */
232 if (md_out_size != NULL)
233 *md_out_size = 0;
234 return ossl_assert(0);
235 }
236
237 if (!ossl_assert(md_length_size <= MAX_HASH_BIT_COUNT_BYTES)
238 || !ossl_assert(md_block_size <= MAX_HASH_BLOCK_SIZE)
239 || !ossl_assert(md_size <= EVP_MAX_MD_SIZE))
240 return 0;
241
242 header_length = 13;
243 if (is_sslv3) {
244 header_length = mac_secret_length + sslv3_pad_length + 8 /* sequence
245 * number */ +
246 1 /* record type */ +
247 2 /* record length */ ;
248 }
249
250 /*
251 * variance_blocks is the number of blocks of the hash that we have to
252 * calculate in constant time because they could be altered by the
253 * padding value. In SSLv3, the padding must be minimal so the end of
254 * the plaintext varies by, at most, 15+20 = 35 bytes. (We conservatively
255 * assume that the MAC size varies from 0..20 bytes.) In case the 9 bytes
256 * of hash termination (0x80 + 64-bit length) don't fit in the final
257 * block, we say that the final two blocks can vary based on the padding.
258 * TLSv1 has MACs up to 48 bytes long (SHA-384) and the padding is not
259 * required to be minimal. Therefore we say that the final |variance_blocks|
260 * blocks can
261 * vary based on the padding. Later in the function, if the message is
262 * short and there obviously cannot be this many blocks then
263 * variance_blocks can be reduced.
264 */
265 variance_blocks = is_sslv3 ? 2 : ( ((255 + 1 + md_size + md_block_size - 1) / md_block_size) + 1);
266 /*
267 * From now on we're dealing with the MAC, which conceptually has 13
268 * bytes of `header' before the start of the data (TLS) or 71/75 bytes
269 * (SSLv3)
270 */
271 len = data_plus_mac_plus_padding_size + header_length;
272 /*
273 * max_mac_bytes contains the maximum bytes of bytes in the MAC,
274 * including * |header|, assuming that there's no padding.
275 */
276 max_mac_bytes = len - md_size - 1;
277 /* num_blocks is the maximum number of hash blocks. */
278 num_blocks =
279 (max_mac_bytes + 1 + md_length_size + md_block_size -
280 1) / md_block_size;
281 /*
282 * In order to calculate the MAC in constant time we have to handle the
283 * final blocks specially because the padding value could cause the end
284 * to appear somewhere in the final |variance_blocks| blocks and we can't
285 * leak where. However, |num_starting_blocks| worth of data can be hashed
286 * right away because no padding value can affect whether they are
287 * plaintext.
288 */
289 num_starting_blocks = 0;
290 /*
291 * k is the starting byte offset into the conceptual header||data where
292 * we start processing.
293 */
294 k = 0;
295 /*
296 * mac_end_offset is the index just past the end of the data to be MACed.
297 */
298 mac_end_offset = data_plus_mac_size + header_length - md_size;
299 /*
300 * c is the index of the 0x80 byte in the final hash block that contains
301 * application data.
302 */
303 c = mac_end_offset % md_block_size;
304 /*
305 * index_a is the hash block number that contains the 0x80 terminating
306 * value.
307 */
308 index_a = mac_end_offset / md_block_size;
309 /*
310 * index_b is the hash block number that contains the 64-bit hash length,
311 * in bits.
312 */
313 index_b = (mac_end_offset + md_length_size) / md_block_size;
314 /*
315 * bits is the hash-length in bits. It includes the additional hash block
316 * for the masked HMAC key, or whole of |header| in the case of SSLv3.
317 */
318
319 /*
320 * For SSLv3, if we're going to have any starting blocks then we need at
321 * least two because the header is larger than a single block.
322 */
323 if (num_blocks > variance_blocks + (is_sslv3 ? 1 : 0)) {
324 num_starting_blocks = num_blocks - variance_blocks;
325 k = md_block_size * num_starting_blocks;
326 }
327
328 bits = 8 * mac_end_offset;
329 if (!is_sslv3) {
330 /*
331 * Compute the initial HMAC block. For SSLv3, the padding and secret
332 * bytes are included in |header| because they take more than a
333 * single block.
334 */
335 bits += 8 * md_block_size;
336 memset(hmac_pad, 0, md_block_size);
337 if (!ossl_assert(mac_secret_length <= sizeof(hmac_pad)))
338 return 0;
339 memcpy(hmac_pad, mac_secret, mac_secret_length);
340 for (i = 0; i < md_block_size; i++)
341 hmac_pad[i] ^= 0x36;
342
343 md_transform(md_state.c, hmac_pad);
344 }
345
346 if (length_is_big_endian) {
347 memset(length_bytes, 0, md_length_size - 4);
348 length_bytes[md_length_size - 4] = (unsigned char)(bits >> 24);
349 length_bytes[md_length_size - 3] = (unsigned char)(bits >> 16);
350 length_bytes[md_length_size - 2] = (unsigned char)(bits >> 8);
351 length_bytes[md_length_size - 1] = (unsigned char)bits;
352 } else {
353 memset(length_bytes, 0, md_length_size);
354 length_bytes[md_length_size - 5] = (unsigned char)(bits >> 24);
355 length_bytes[md_length_size - 6] = (unsigned char)(bits >> 16);
356 length_bytes[md_length_size - 7] = (unsigned char)(bits >> 8);
357 length_bytes[md_length_size - 8] = (unsigned char)bits;
358 }
359
360 if (k > 0) {
361 if (is_sslv3) {
362 size_t overhang;
363
364 /*
365 * The SSLv3 header is larger than a single block. overhang is
366 * the number of bytes beyond a single block that the header
367 * consumes: either 7 bytes (SHA1) or 11 bytes (MD5). There are no
368 * ciphersuites in SSLv3 that are not SHA1 or MD5 based and
369 * therefore we can be confident that the header_length will be
370 * greater than |md_block_size|. However we add a sanity check just
371 * in case
372 */
373 if (header_length <= md_block_size) {
374 /* Should never happen */
375 return 0;
376 }
377 overhang = header_length - md_block_size;
378 md_transform(md_state.c, header);
379 memcpy(first_block, header + md_block_size, overhang);
380 memcpy(first_block + overhang, data, md_block_size - overhang);
381 md_transform(md_state.c, first_block);
382 for (i = 1; i < k / md_block_size - 1; i++)
383 md_transform(md_state.c, data + md_block_size * i - overhang);
384 } else {
385 /* k is a multiple of md_block_size. */
386 memcpy(first_block, header, 13);
387 memcpy(first_block + 13, data, md_block_size - 13);
388 md_transform(md_state.c, first_block);
389 for (i = 1; i < k / md_block_size; i++)
390 md_transform(md_state.c, data + md_block_size * i - 13);
391 }
392 }
393
394 memset(mac_out, 0, sizeof(mac_out));
395
396 /*
397 * We now process the final hash blocks. For each block, we construct it
398 * in constant time. If the |i==index_a| then we'll include the 0x80
399 * bytes and zero pad etc. For each block we selectively copy it, in
400 * constant time, to |mac_out|.
401 */
402 for (i = num_starting_blocks; i <= num_starting_blocks + variance_blocks;
403 i++) {
404 unsigned char block[MAX_HASH_BLOCK_SIZE];
405 unsigned char is_block_a = constant_time_eq_8_s(i, index_a);
406 unsigned char is_block_b = constant_time_eq_8_s(i, index_b);
407 for (j = 0; j < md_block_size; j++) {
408 unsigned char b = 0, is_past_c, is_past_cp1;
409 if (k < header_length)
410 b = header[k];
411 else if (k < data_plus_mac_plus_padding_size + header_length)
412 b = data[k - header_length];
413 k++;
414
415 is_past_c = is_block_a & constant_time_ge_8_s(j, c);
416 is_past_cp1 = is_block_a & constant_time_ge_8_s(j, c + 1);
417 /*
418 * If this is the block containing the end of the application
419 * data, and we are at the offset for the 0x80 value, then
420 * overwrite b with 0x80.
421 */
422 b = constant_time_select_8(is_past_c, 0x80, b);
423 /*
424 * If this block contains the end of the application data
425 * and we're past the 0x80 value then just write zero.
426 */
427 b = b & ~is_past_cp1;
428 /*
429 * If this is index_b (the final block), but not index_a (the end
430 * of the data), then the 64-bit length didn't fit into index_a
431 * and we're having to add an extra block of zeros.
432 */
433 b &= ~is_block_b | is_block_a;
434
435 /*
436 * The final bytes of one of the blocks contains the length.
437 */
438 if (j >= md_block_size - md_length_size) {
439 /* If this is index_b, write a length byte. */
440 b = constant_time_select_8(is_block_b,
441 length_bytes[j -
442 (md_block_size -
443 md_length_size)], b);
444 }
445 block[j] = b;
446 }
447
448 md_transform(md_state.c, block);
449 md_final_raw(md_state.c, block);
450 /* If this is index_b, copy the hash value to |mac_out|. */
451 for (j = 0; j < md_size; j++)
452 mac_out[j] |= block[j] & is_block_b;
453 }
454
455 md_ctx = EVP_MD_CTX_new();
456 if (md_ctx == NULL)
457 goto err;
458 if (EVP_DigestInit_ex(md_ctx, EVP_MD_CTX_md(ctx), NULL /* engine */ ) <= 0)
459 goto err;
460 if (is_sslv3) {
461 /* We repurpose |hmac_pad| to contain the SSLv3 pad2 block. */
462 memset(hmac_pad, 0x5c, sslv3_pad_length);
463
464 if (EVP_DigestUpdate(md_ctx, mac_secret, mac_secret_length) <= 0
465 || EVP_DigestUpdate(md_ctx, hmac_pad, sslv3_pad_length) <= 0
466 || EVP_DigestUpdate(md_ctx, mac_out, md_size) <= 0)
467 goto err;
468 } else {
469 /* Complete the HMAC in the standard manner. */
470 for (i = 0; i < md_block_size; i++)
471 hmac_pad[i] ^= 0x6a;
472
473 if (EVP_DigestUpdate(md_ctx, hmac_pad, md_block_size) <= 0
474 || EVP_DigestUpdate(md_ctx, mac_out, md_size) <= 0)
475 goto err;
476 }
477 /* TODO(size_t): Convert me */
478 ret = EVP_DigestFinal(md_ctx, md_out, &md_out_size_u);
479 if (ret && md_out_size)
480 *md_out_size = md_out_size_u;
481 EVP_MD_CTX_free(md_ctx);
482
483 return 1;
484 err:
485 EVP_MD_CTX_free(md_ctx);
486 return 0;
487 }
488