1 /*
2 * Copyright 2012-2021 The OpenSSL Project Authors. All Rights Reserved.
3 *
4 * Licensed under the Apache License 2.0 (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 /*
11 * This file has no dependencies on the rest of libssl because it is shared
12 * with the providers. It contains functions for low level MAC calculations.
13 * Responsibility for this lies with the HMAC implementation in the
14 * providers. However there are legacy code paths in libssl which also need to
15 * do this. In time those legacy code paths can be removed and this file can be
16 * moved out of libssl.
17 */
18
19
20 /*
21 * MD5 and SHA-1 low level APIs are deprecated for public use, but still ok for
22 * internal use.
23 */
24 #include "internal/deprecated.h"
25
26 #include "internal/constant_time.h"
27 #include "internal/cryptlib.h"
28
29 #include <openssl/evp.h>
30 #ifndef FIPS_MODULE
31 # include <openssl/md5.h>
32 #endif
33 #include <openssl/sha.h>
34
35 char ssl3_cbc_record_digest_supported(const EVP_MD_CTX *ctx);
36 int ssl3_cbc_digest_record(const EVP_MD *md,
37 unsigned char *md_out,
38 size_t *md_out_size,
39 const unsigned char *header,
40 const unsigned char *data,
41 size_t data_size,
42 size_t data_plus_mac_plus_padding_size,
43 const unsigned char *mac_secret,
44 size_t mac_secret_length, char is_sslv3);
45
46 # define l2n(l,c) (*((c)++)=(unsigned char)(((l)>>24)&0xff), \
47 *((c)++)=(unsigned char)(((l)>>16)&0xff), \
48 *((c)++)=(unsigned char)(((l)>> 8)&0xff), \
49 *((c)++)=(unsigned char)(((l) )&0xff))
50
51 # define l2n6(l,c) (*((c)++)=(unsigned char)(((l)>>40)&0xff), \
52 *((c)++)=(unsigned char)(((l)>>32)&0xff), \
53 *((c)++)=(unsigned char)(((l)>>24)&0xff), \
54 *((c)++)=(unsigned char)(((l)>>16)&0xff), \
55 *((c)++)=(unsigned char)(((l)>> 8)&0xff), \
56 *((c)++)=(unsigned char)(((l) )&0xff))
57
58 # define l2n8(l,c) (*((c)++)=(unsigned char)(((l)>>56)&0xff), \
59 *((c)++)=(unsigned char)(((l)>>48)&0xff), \
60 *((c)++)=(unsigned char)(((l)>>40)&0xff), \
61 *((c)++)=(unsigned char)(((l)>>32)&0xff), \
62 *((c)++)=(unsigned char)(((l)>>24)&0xff), \
63 *((c)++)=(unsigned char)(((l)>>16)&0xff), \
64 *((c)++)=(unsigned char)(((l)>> 8)&0xff), \
65 *((c)++)=(unsigned char)(((l) )&0xff))
66
67 /*
68 * MAX_HASH_BIT_COUNT_BYTES is the maximum number of bytes in the hash's
69 * length field. (SHA-384/512 have 128-bit length.)
70 */
71 #define MAX_HASH_BIT_COUNT_BYTES 16
72
73 /*
74 * MAX_HASH_BLOCK_SIZE is the maximum hash block size that we'll support.
75 * Currently SHA-384/512 has a 128-byte block size and that's the largest
76 * supported by TLS.)
77 */
78 #define MAX_HASH_BLOCK_SIZE 128
79
80 #ifndef FIPS_MODULE
81 /*
82 * u32toLE serializes an unsigned, 32-bit number (n) as four bytes at (p) in
83 * little-endian order. The value of p is advanced by four.
84 */
85 # define u32toLE(n, p) \
86 (*((p)++)=(unsigned char)(n), \
87 *((p)++)=(unsigned char)(n>>8), \
88 *((p)++)=(unsigned char)(n>>16), \
89 *((p)++)=(unsigned char)(n>>24))
90
91 /*
92 * These functions serialize the state of a hash and thus perform the
93 * standard "final" operation without adding the padding and length that such
94 * a function typically does.
95 */
tls1_md5_final_raw(void * ctx,unsigned char * md_out)96 static void tls1_md5_final_raw(void *ctx, unsigned char *md_out)
97 {
98 MD5_CTX *md5 = ctx;
99 u32toLE(md5->A, md_out);
100 u32toLE(md5->B, md_out);
101 u32toLE(md5->C, md_out);
102 u32toLE(md5->D, md_out);
103 }
104 #endif /* FIPS_MODULE */
105
tls1_sha1_final_raw(void * ctx,unsigned char * md_out)106 static void tls1_sha1_final_raw(void *ctx, unsigned char *md_out)
107 {
108 SHA_CTX *sha1 = ctx;
109 l2n(sha1->h0, md_out);
110 l2n(sha1->h1, md_out);
111 l2n(sha1->h2, md_out);
112 l2n(sha1->h3, md_out);
113 l2n(sha1->h4, md_out);
114 }
115
tls1_sha256_final_raw(void * ctx,unsigned char * md_out)116 static void tls1_sha256_final_raw(void *ctx, unsigned char *md_out)
117 {
118 SHA256_CTX *sha256 = ctx;
119 unsigned i;
120
121 for (i = 0; i < 8; i++) {
122 l2n(sha256->h[i], md_out);
123 }
124 }
125
tls1_sha512_final_raw(void * ctx,unsigned char * md_out)126 static void tls1_sha512_final_raw(void *ctx, unsigned char *md_out)
127 {
128 SHA512_CTX *sha512 = ctx;
129 unsigned i;
130
131 for (i = 0; i < 8; i++) {
132 l2n8(sha512->h[i], md_out);
133 }
134 }
135
136 #undef LARGEST_DIGEST_CTX
137 #define LARGEST_DIGEST_CTX SHA512_CTX
138
139 /*-
140 * ssl3_cbc_digest_record computes the MAC of a decrypted, padded SSLv3/TLS
141 * record.
142 *
143 * ctx: the EVP_MD_CTX from which we take the hash function.
144 * ssl3_cbc_record_digest_supported must return true for this EVP_MD_CTX.
145 * md_out: the digest output. At most EVP_MAX_MD_SIZE bytes will be written.
146 * md_out_size: if non-NULL, the number of output bytes is written here.
147 * header: the 13-byte, TLS record header.
148 * data: the record data itself, less any preceding explicit IV.
149 * data_size: the secret, reported length of the data once the MAC and padding
150 * has been removed.
151 * data_plus_mac_plus_padding_size: the public length of the whole
152 * record, including MAC and padding.
153 * is_sslv3: non-zero if we are to use SSLv3. Otherwise, TLS.
154 *
155 * On entry: we know that data is data_plus_mac_plus_padding_size in length
156 * Returns 1 on success or 0 on error
157 */
ssl3_cbc_digest_record(const EVP_MD * md,unsigned char * md_out,size_t * md_out_size,const unsigned char * header,const unsigned char * data,size_t data_size,size_t data_plus_mac_plus_padding_size,const unsigned char * mac_secret,size_t mac_secret_length,char is_sslv3)158 int ssl3_cbc_digest_record(const EVP_MD *md,
159 unsigned char *md_out,
160 size_t *md_out_size,
161 const unsigned char *header,
162 const unsigned char *data,
163 size_t data_size,
164 size_t data_plus_mac_plus_padding_size,
165 const unsigned char *mac_secret,
166 size_t mac_secret_length, char is_sslv3)
167 {
168 union {
169 OSSL_UNION_ALIGN;
170 unsigned char c[sizeof(LARGEST_DIGEST_CTX)];
171 } md_state;
172 void (*md_final_raw) (void *ctx, unsigned char *md_out);
173 void (*md_transform) (void *ctx, const unsigned char *block);
174 size_t md_size, md_block_size = 64;
175 size_t sslv3_pad_length = 40, header_length, variance_blocks,
176 len, max_mac_bytes, num_blocks,
177 num_starting_blocks, k, mac_end_offset, c, index_a, index_b;
178 size_t bits; /* at most 18 bits */
179 unsigned char length_bytes[MAX_HASH_BIT_COUNT_BYTES];
180 /* hmac_pad is the masked HMAC key. */
181 unsigned char hmac_pad[MAX_HASH_BLOCK_SIZE];
182 unsigned char first_block[MAX_HASH_BLOCK_SIZE];
183 unsigned char mac_out[EVP_MAX_MD_SIZE];
184 size_t i, j;
185 unsigned md_out_size_u;
186 EVP_MD_CTX *md_ctx = NULL;
187 /*
188 * mdLengthSize is the number of bytes in the length field that
189 * terminates * the hash.
190 */
191 size_t md_length_size = 8;
192 char length_is_big_endian = 1;
193 int ret = 0;
194
195 /*
196 * This is a, hopefully redundant, check that allows us to forget about
197 * many possible overflows later in this function.
198 */
199 if (!ossl_assert(data_plus_mac_plus_padding_size < 1024 * 1024))
200 return 0;
201
202 if (EVP_MD_is_a(md, "MD5")) {
203 #ifdef FIPS_MODULE
204 return 0;
205 #else
206 if (MD5_Init((MD5_CTX *)md_state.c) <= 0)
207 return 0;
208 md_final_raw = tls1_md5_final_raw;
209 md_transform =
210 (void (*)(void *ctx, const unsigned char *block))MD5_Transform;
211 md_size = 16;
212 sslv3_pad_length = 48;
213 length_is_big_endian = 0;
214 #endif
215 } else if (EVP_MD_is_a(md, "SHA1")) {
216 if (SHA1_Init((SHA_CTX *)md_state.c) <= 0)
217 return 0;
218 md_final_raw = tls1_sha1_final_raw;
219 md_transform =
220 (void (*)(void *ctx, const unsigned char *block))SHA1_Transform;
221 md_size = 20;
222 } else if (EVP_MD_is_a(md, "SHA2-224")) {
223 if (SHA224_Init((SHA256_CTX *)md_state.c) <= 0)
224 return 0;
225 md_final_raw = tls1_sha256_final_raw;
226 md_transform =
227 (void (*)(void *ctx, const unsigned char *block))SHA256_Transform;
228 md_size = 224 / 8;
229 } else if (EVP_MD_is_a(md, "SHA2-256")) {
230 if (SHA256_Init((SHA256_CTX *)md_state.c) <= 0)
231 return 0;
232 md_final_raw = tls1_sha256_final_raw;
233 md_transform =
234 (void (*)(void *ctx, const unsigned char *block))SHA256_Transform;
235 md_size = 32;
236 } else if (EVP_MD_is_a(md, "SHA2-384")) {
237 if (SHA384_Init((SHA512_CTX *)md_state.c) <= 0)
238 return 0;
239 md_final_raw = tls1_sha512_final_raw;
240 md_transform =
241 (void (*)(void *ctx, const unsigned char *block))SHA512_Transform;
242 md_size = 384 / 8;
243 md_block_size = 128;
244 md_length_size = 16;
245 } else if (EVP_MD_is_a(md, "SHA2-512")) {
246 if (SHA512_Init((SHA512_CTX *)md_state.c) <= 0)
247 return 0;
248 md_final_raw = tls1_sha512_final_raw;
249 md_transform =
250 (void (*)(void *ctx, const unsigned char *block))SHA512_Transform;
251 md_size = 64;
252 md_block_size = 128;
253 md_length_size = 16;
254 } else {
255 /*
256 * ssl3_cbc_record_digest_supported should have been called first to
257 * check that the hash function is supported.
258 */
259 if (md_out_size != NULL)
260 *md_out_size = 0;
261 return ossl_assert(0);
262 }
263
264 if (!ossl_assert(md_length_size <= MAX_HASH_BIT_COUNT_BYTES)
265 || !ossl_assert(md_block_size <= MAX_HASH_BLOCK_SIZE)
266 || !ossl_assert(md_size <= EVP_MAX_MD_SIZE))
267 return 0;
268
269 header_length = 13;
270 if (is_sslv3) {
271 header_length = mac_secret_length + sslv3_pad_length + 8 /* sequence
272 * number */ +
273 1 /* record type */ +
274 2 /* record length */ ;
275 }
276
277 /*
278 * variance_blocks is the number of blocks of the hash that we have to
279 * calculate in constant time because they could be altered by the
280 * padding value. In SSLv3, the padding must be minimal so the end of
281 * the plaintext varies by, at most, 15+20 = 35 bytes. (We conservatively
282 * assume that the MAC size varies from 0..20 bytes.) In case the 9 bytes
283 * of hash termination (0x80 + 64-bit length) don't fit in the final
284 * block, we say that the final two blocks can vary based on the padding.
285 * TLSv1 has MACs up to 48 bytes long (SHA-384) and the padding is not
286 * required to be minimal. Therefore we say that the final |variance_blocks|
287 * blocks can
288 * vary based on the padding. Later in the function, if the message is
289 * short and there obviously cannot be this many blocks then
290 * variance_blocks can be reduced.
291 */
292 variance_blocks = is_sslv3 ? 2 : ( ((255 + 1 + md_size + md_block_size - 1) / md_block_size) + 1);
293 /*
294 * From now on we're dealing with the MAC, which conceptually has 13
295 * bytes of `header' before the start of the data (TLS) or 71/75 bytes
296 * (SSLv3)
297 */
298 len = data_plus_mac_plus_padding_size + header_length;
299 /*
300 * max_mac_bytes contains the maximum bytes of bytes in the MAC,
301 * including * |header|, assuming that there's no padding.
302 */
303 max_mac_bytes = len - md_size - 1;
304 /* num_blocks is the maximum number of hash blocks. */
305 num_blocks =
306 (max_mac_bytes + 1 + md_length_size + md_block_size -
307 1) / md_block_size;
308 /*
309 * In order to calculate the MAC in constant time we have to handle the
310 * final blocks specially because the padding value could cause the end
311 * to appear somewhere in the final |variance_blocks| blocks and we can't
312 * leak where. However, |num_starting_blocks| worth of data can be hashed
313 * right away because no padding value can affect whether they are
314 * plaintext.
315 */
316 num_starting_blocks = 0;
317 /*
318 * k is the starting byte offset into the conceptual header||data where
319 * we start processing.
320 */
321 k = 0;
322 /*
323 * mac_end_offset is the index just past the end of the data to be MACed.
324 */
325 mac_end_offset = data_size + header_length;
326 /*
327 * c is the index of the 0x80 byte in the final hash block that contains
328 * application data.
329 */
330 c = mac_end_offset % md_block_size;
331 /*
332 * index_a is the hash block number that contains the 0x80 terminating
333 * value.
334 */
335 index_a = mac_end_offset / md_block_size;
336 /*
337 * index_b is the hash block number that contains the 64-bit hash length,
338 * in bits.
339 */
340 index_b = (mac_end_offset + md_length_size) / md_block_size;
341 /*
342 * bits is the hash-length in bits. It includes the additional hash block
343 * for the masked HMAC key, or whole of |header| in the case of SSLv3.
344 */
345
346 /*
347 * For SSLv3, if we're going to have any starting blocks then we need at
348 * least two because the header is larger than a single block.
349 */
350 if (num_blocks > variance_blocks + (is_sslv3 ? 1 : 0)) {
351 num_starting_blocks = num_blocks - variance_blocks;
352 k = md_block_size * num_starting_blocks;
353 }
354
355 bits = 8 * mac_end_offset;
356 if (!is_sslv3) {
357 /*
358 * Compute the initial HMAC block. For SSLv3, the padding and secret
359 * bytes are included in |header| because they take more than a
360 * single block.
361 */
362 bits += 8 * md_block_size;
363 memset(hmac_pad, 0, md_block_size);
364 if (!ossl_assert(mac_secret_length <= sizeof(hmac_pad)))
365 return 0;
366 memcpy(hmac_pad, mac_secret, mac_secret_length);
367 for (i = 0; i < md_block_size; i++)
368 hmac_pad[i] ^= 0x36;
369
370 md_transform(md_state.c, hmac_pad);
371 }
372
373 if (length_is_big_endian) {
374 memset(length_bytes, 0, md_length_size - 4);
375 length_bytes[md_length_size - 4] = (unsigned char)(bits >> 24);
376 length_bytes[md_length_size - 3] = (unsigned char)(bits >> 16);
377 length_bytes[md_length_size - 2] = (unsigned char)(bits >> 8);
378 length_bytes[md_length_size - 1] = (unsigned char)bits;
379 } else {
380 memset(length_bytes, 0, md_length_size);
381 length_bytes[md_length_size - 5] = (unsigned char)(bits >> 24);
382 length_bytes[md_length_size - 6] = (unsigned char)(bits >> 16);
383 length_bytes[md_length_size - 7] = (unsigned char)(bits >> 8);
384 length_bytes[md_length_size - 8] = (unsigned char)bits;
385 }
386
387 if (k > 0) {
388 if (is_sslv3) {
389 size_t overhang;
390
391 /*
392 * The SSLv3 header is larger than a single block. overhang is
393 * the number of bytes beyond a single block that the header
394 * consumes: either 7 bytes (SHA1) or 11 bytes (MD5). There are no
395 * ciphersuites in SSLv3 that are not SHA1 or MD5 based and
396 * therefore we can be confident that the header_length will be
397 * greater than |md_block_size|. However we add a sanity check just
398 * in case
399 */
400 if (header_length <= md_block_size) {
401 /* Should never happen */
402 return 0;
403 }
404 overhang = header_length - md_block_size;
405 md_transform(md_state.c, header);
406 memcpy(first_block, header + md_block_size, overhang);
407 memcpy(first_block + overhang, data, md_block_size - overhang);
408 md_transform(md_state.c, first_block);
409 for (i = 1; i < k / md_block_size - 1; i++)
410 md_transform(md_state.c, data + md_block_size * i - overhang);
411 } else {
412 /* k is a multiple of md_block_size. */
413 memcpy(first_block, header, 13);
414 memcpy(first_block + 13, data, md_block_size - 13);
415 md_transform(md_state.c, first_block);
416 for (i = 1; i < k / md_block_size; i++)
417 md_transform(md_state.c, data + md_block_size * i - 13);
418 }
419 }
420
421 memset(mac_out, 0, sizeof(mac_out));
422
423 /*
424 * We now process the final hash blocks. For each block, we construct it
425 * in constant time. If the |i==index_a| then we'll include the 0x80
426 * bytes and zero pad etc. For each block we selectively copy it, in
427 * constant time, to |mac_out|.
428 */
429 for (i = num_starting_blocks; i <= num_starting_blocks + variance_blocks;
430 i++) {
431 unsigned char block[MAX_HASH_BLOCK_SIZE];
432 unsigned char is_block_a = constant_time_eq_8_s(i, index_a);
433 unsigned char is_block_b = constant_time_eq_8_s(i, index_b);
434 for (j = 0; j < md_block_size; j++) {
435 unsigned char b = 0, is_past_c, is_past_cp1;
436 if (k < header_length)
437 b = header[k];
438 else if (k < data_plus_mac_plus_padding_size + header_length)
439 b = data[k - header_length];
440 k++;
441
442 is_past_c = is_block_a & constant_time_ge_8_s(j, c);
443 is_past_cp1 = is_block_a & constant_time_ge_8_s(j, c + 1);
444 /*
445 * If this is the block containing the end of the application
446 * data, and we are at the offset for the 0x80 value, then
447 * overwrite b with 0x80.
448 */
449 b = constant_time_select_8(is_past_c, 0x80, b);
450 /*
451 * If this block contains the end of the application data
452 * and we're past the 0x80 value then just write zero.
453 */
454 b = b & ~is_past_cp1;
455 /*
456 * If this is index_b (the final block), but not index_a (the end
457 * of the data), then the 64-bit length didn't fit into index_a
458 * and we're having to add an extra block of zeros.
459 */
460 b &= ~is_block_b | is_block_a;
461
462 /*
463 * The final bytes of one of the blocks contains the length.
464 */
465 if (j >= md_block_size - md_length_size) {
466 /* If this is index_b, write a length byte. */
467 b = constant_time_select_8(is_block_b,
468 length_bytes[j -
469 (md_block_size -
470 md_length_size)], b);
471 }
472 block[j] = b;
473 }
474
475 md_transform(md_state.c, block);
476 md_final_raw(md_state.c, block);
477 /* If this is index_b, copy the hash value to |mac_out|. */
478 for (j = 0; j < md_size; j++)
479 mac_out[j] |= block[j] & is_block_b;
480 }
481
482 md_ctx = EVP_MD_CTX_new();
483 if (md_ctx == NULL)
484 goto err;
485
486 if (EVP_DigestInit_ex(md_ctx, md, NULL /* engine */ ) <= 0)
487 goto err;
488 if (is_sslv3) {
489 /* We repurpose |hmac_pad| to contain the SSLv3 pad2 block. */
490 memset(hmac_pad, 0x5c, sslv3_pad_length);
491
492 if (EVP_DigestUpdate(md_ctx, mac_secret, mac_secret_length) <= 0
493 || EVP_DigestUpdate(md_ctx, hmac_pad, sslv3_pad_length) <= 0
494 || EVP_DigestUpdate(md_ctx, mac_out, md_size) <= 0)
495 goto err;
496 } else {
497 /* Complete the HMAC in the standard manner. */
498 for (i = 0; i < md_block_size; i++)
499 hmac_pad[i] ^= 0x6a;
500
501 if (EVP_DigestUpdate(md_ctx, hmac_pad, md_block_size) <= 0
502 || EVP_DigestUpdate(md_ctx, mac_out, md_size) <= 0)
503 goto err;
504 }
505 ret = EVP_DigestFinal(md_ctx, md_out, &md_out_size_u);
506 if (ret && md_out_size)
507 *md_out_size = md_out_size_u;
508
509 ret = 1;
510 err:
511 EVP_MD_CTX_free(md_ctx);
512 return ret;
513 }
514