1 /*
2 * Copyright 2012-2023 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 * MD5 and SHA-1 low level APIs are deprecated for public use, but still ok for
21 * internal use.
22 */
23 #include "internal/deprecated.h"
24
25 #include <openssl/evp.h>
26 #ifndef FIPS_MODULE
27 # include <openssl/md5.h>
28 #endif
29 #include <openssl/sha.h>
30
31 #include "internal/ssl3_cbc.h"
32 #include "internal/constant_time.h"
33 #include "internal/cryptlib.h"
34
35 /*
36 * MAX_HASH_BIT_COUNT_BYTES is the maximum number of bytes in the hash's
37 * length field. (SHA-384/512 have 128-bit length.)
38 */
39 #define MAX_HASH_BIT_COUNT_BYTES 16
40
41 /*
42 * MAX_HASH_BLOCK_SIZE is the maximum hash block size that we'll support.
43 * Currently SHA-384/512 has a 128-byte block size and that's the largest
44 * supported by TLS.)
45 */
46 #define MAX_HASH_BLOCK_SIZE 128
47
48 #ifndef FIPS_MODULE
49 /*
50 * u32toLE serializes an unsigned, 32-bit number (n) as four bytes at (p) in
51 * little-endian order. The value of p is advanced by four.
52 */
53 # define u32toLE(n, p) \
54 (*((p)++) = (unsigned char)(n ), \
55 *((p)++) = (unsigned char)(n >> 8), \
56 *((p)++) = (unsigned char)(n >> 16), \
57 *((p)++) = (unsigned char)(n >> 24))
58
59 /*
60 * These functions serialize the state of a hash and thus perform the
61 * standard "final" operation without adding the padding and length that such
62 * a function typically does.
63 */
tls1_md5_final_raw(void * ctx,unsigned char * md_out)64 static void tls1_md5_final_raw(void *ctx, unsigned char *md_out)
65 {
66 MD5_CTX *md5 = ctx;
67
68 u32toLE(md5->A, md_out);
69 u32toLE(md5->B, md_out);
70 u32toLE(md5->C, md_out);
71 u32toLE(md5->D, md_out);
72 }
73 #endif /* FIPS_MODULE */
74
tls1_sha1_final_raw(void * ctx,unsigned char * md_out)75 static void tls1_sha1_final_raw(void *ctx, unsigned char *md_out)
76 {
77 SHA_CTX *sha1 = ctx;
78
79 l2n(sha1->h0, md_out);
80 l2n(sha1->h1, md_out);
81 l2n(sha1->h2, md_out);
82 l2n(sha1->h3, md_out);
83 l2n(sha1->h4, md_out);
84 }
85
tls1_sha256_final_raw(void * ctx,unsigned char * md_out)86 static void tls1_sha256_final_raw(void *ctx, unsigned char *md_out)
87 {
88 SHA256_CTX *sha256 = ctx;
89 unsigned i;
90
91 for (i = 0; i < 8; i++)
92 l2n(sha256->h[i], md_out);
93 }
94
tls1_sha512_final_raw(void * ctx,unsigned char * md_out)95 static void tls1_sha512_final_raw(void *ctx, unsigned char *md_out)
96 {
97 SHA512_CTX *sha512 = ctx;
98 unsigned i;
99
100 for (i = 0; i < 8; i++)
101 l2n8(sha512->h[i], md_out);
102 }
103
104 #undef LARGEST_DIGEST_CTX
105 #define LARGEST_DIGEST_CTX SHA512_CTX
106
107 /*-
108 * ssl3_cbc_digest_record computes the MAC of a decrypted, padded SSLv3/TLS
109 * record.
110 *
111 * ctx: the EVP_MD_CTX from which we take the hash function.
112 * ssl3_cbc_record_digest_supported must return true for this EVP_MD_CTX.
113 * md_out: the digest output. At most EVP_MAX_MD_SIZE bytes will be written.
114 * md_out_size: if non-NULL, the number of output bytes is written here.
115 * header: the 13-byte, TLS record header.
116 * data: the record data itself, less any preceding explicit IV.
117 * data_size: the secret, reported length of the data once the MAC and padding
118 * has been removed.
119 * data_plus_mac_plus_padding_size: the public length of the whole
120 * record, including MAC and padding.
121 * is_sslv3: non-zero if we are to use SSLv3. Otherwise, TLS.
122 *
123 * On entry: we know that data is data_plus_mac_plus_padding_size in length
124 * Returns 1 on success or 0 on error
125 */
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)126 int ssl3_cbc_digest_record(const EVP_MD *md,
127 unsigned char *md_out,
128 size_t *md_out_size,
129 const unsigned char *header,
130 const unsigned char *data,
131 size_t data_size,
132 size_t data_plus_mac_plus_padding_size,
133 const unsigned char *mac_secret,
134 size_t mac_secret_length, char is_sslv3)
135 {
136 union {
137 OSSL_UNION_ALIGN;
138 unsigned char c[sizeof(LARGEST_DIGEST_CTX)];
139 } md_state;
140 void (*md_final_raw) (void *ctx, unsigned char *md_out);
141 void (*md_transform) (void *ctx, const unsigned char *block);
142 size_t md_size, md_block_size = 64;
143 size_t sslv3_pad_length = 40, header_length, variance_blocks,
144 len, max_mac_bytes, num_blocks,
145 num_starting_blocks, k, mac_end_offset, c, index_a, index_b;
146 size_t bits; /* at most 18 bits */
147 unsigned char length_bytes[MAX_HASH_BIT_COUNT_BYTES];
148 /* hmac_pad is the masked HMAC key. */
149 unsigned char hmac_pad[MAX_HASH_BLOCK_SIZE];
150 unsigned char first_block[MAX_HASH_BLOCK_SIZE];
151 unsigned char mac_out[EVP_MAX_MD_SIZE];
152 size_t i, j;
153 unsigned md_out_size_u;
154 EVP_MD_CTX *md_ctx = NULL;
155 /*
156 * mdLengthSize is the number of bytes in the length field that
157 * terminates * the hash.
158 */
159 size_t md_length_size = 8;
160 char length_is_big_endian = 1;
161 int ret = 0;
162
163 /*
164 * This is a, hopefully redundant, check that allows us to forget about
165 * many possible overflows later in this function.
166 */
167 if (!ossl_assert(data_plus_mac_plus_padding_size < 1024 * 1024))
168 return 0;
169
170 if (EVP_MD_is_a(md, "MD5")) {
171 #ifdef FIPS_MODULE
172 return 0;
173 #else
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 #endif
183 } else if (EVP_MD_is_a(md, "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 } else if (EVP_MD_is_a(md, "SHA2-224")) {
191 if (SHA224_Init((SHA256_CTX *)md_state.c) <= 0)
192 return 0;
193 md_final_raw = tls1_sha256_final_raw;
194 md_transform =
195 (void (*)(void *ctx, const unsigned char *block))SHA256_Transform;
196 md_size = 224 / 8;
197 } else if (EVP_MD_is_a(md, "SHA2-256")) {
198 if (SHA256_Init((SHA256_CTX *)md_state.c) <= 0)
199 return 0;
200 md_final_raw = tls1_sha256_final_raw;
201 md_transform =
202 (void (*)(void *ctx, const unsigned char *block))SHA256_Transform;
203 md_size = 32;
204 } else if (EVP_MD_is_a(md, "SHA2-384")) {
205 if (SHA384_Init((SHA512_CTX *)md_state.c) <= 0)
206 return 0;
207 md_final_raw = tls1_sha512_final_raw;
208 md_transform =
209 (void (*)(void *ctx, const unsigned char *block))SHA512_Transform;
210 md_size = 384 / 8;
211 md_block_size = 128;
212 md_length_size = 16;
213 } else if (EVP_MD_is_a(md, "SHA2-512")) {
214 if (SHA512_Init((SHA512_CTX *)md_state.c) <= 0)
215 return 0;
216 md_final_raw = tls1_sha512_final_raw;
217 md_transform =
218 (void (*)(void *ctx, const unsigned char *block))SHA512_Transform;
219 md_size = 64;
220 md_block_size = 128;
221 md_length_size = 16;
222 } else {
223 /*
224 * ssl3_cbc_record_digest_supported should have been called first to
225 * check that the hash function is supported.
226 */
227 if (md_out_size != NULL)
228 *md_out_size = 0;
229 return ossl_assert(0);
230 }
231
232 if (!ossl_assert(md_length_size <= MAX_HASH_BIT_COUNT_BYTES)
233 || !ossl_assert(md_block_size <= MAX_HASH_BLOCK_SIZE)
234 || !ossl_assert(md_size <= EVP_MAX_MD_SIZE))
235 return 0;
236
237 header_length = 13;
238 if (is_sslv3) {
239 header_length = mac_secret_length
240 + sslv3_pad_length
241 + 8 /* sequence number */
242 + 1 /* record type */
243 + 2; /* record length */
244 }
245
246 /*
247 * variance_blocks is the number of blocks of the hash that we have to
248 * calculate in constant time because they could be altered by the
249 * padding value. In SSLv3, the padding must be minimal so the end of
250 * the plaintext varies by, at most, 15+20 = 35 bytes. (We conservatively
251 * assume that the MAC size varies from 0..20 bytes.) In case the 9 bytes
252 * of hash termination (0x80 + 64-bit length) don't fit in the final
253 * block, we say that the final two blocks can vary based on the padding.
254 * TLSv1 has MACs up to 48 bytes long (SHA-384) and the padding is not
255 * required to be minimal. Therefore we say that the final |variance_blocks|
256 * blocks can
257 * vary based on the padding. Later in the function, if the message is
258 * short and there obviously cannot be this many blocks then
259 * variance_blocks can be reduced.
260 */
261 variance_blocks = is_sslv3 ? 2
262 : (((255 + 1 + md_size + md_block_size - 1)
263 / md_block_size) + 1);
264 /*
265 * From now on we're dealing with the MAC, which conceptually has 13
266 * bytes of `header' before the start of the data (TLS) or 71/75 bytes
267 * (SSLv3)
268 */
269 len = data_plus_mac_plus_padding_size + header_length;
270 /*
271 * max_mac_bytes contains the maximum bytes of bytes in the MAC,
272 * including * |header|, assuming that there's no padding.
273 */
274 max_mac_bytes = len - md_size - 1;
275 /* num_blocks is the maximum number of hash blocks. */
276 num_blocks =
277 (max_mac_bytes + 1 + md_length_size + md_block_size -
278 1) / md_block_size;
279 /*
280 * In order to calculate the MAC in constant time we have to handle the
281 * final blocks specially because the padding value could cause the end
282 * to appear somewhere in the final |variance_blocks| blocks and we can't
283 * leak where. However, |num_starting_blocks| worth of data can be hashed
284 * right away because no padding value can affect whether they are
285 * plaintext.
286 */
287 num_starting_blocks = 0;
288 /*
289 * k is the starting byte offset into the conceptual header||data where
290 * we start processing.
291 */
292 k = 0;
293 /*
294 * mac_end_offset is the index just past the end of the data to be MACed.
295 */
296 mac_end_offset = data_size + header_length;
297 /*
298 * c is the index of the 0x80 byte in the final hash block that contains
299 * application data.
300 */
301 c = mac_end_offset % md_block_size;
302 /*
303 * index_a is the hash block number that contains the 0x80 terminating
304 * value.
305 */
306 index_a = mac_end_offset / md_block_size;
307 /*
308 * index_b is the hash block number that contains the 64-bit hash length,
309 * in bits.
310 */
311 index_b = (mac_end_offset + md_length_size) / md_block_size;
312 /*
313 * bits is the hash-length in bits. It includes the additional hash block
314 * for the masked HMAC key, or whole of |header| in the case of SSLv3.
315 */
316
317 /*
318 * For SSLv3, if we're going to have any starting blocks then we need at
319 * least two because the header is larger than a single block.
320 */
321 if (num_blocks > variance_blocks + (is_sslv3 ? 1 : 0)) {
322 num_starting_blocks = num_blocks - variance_blocks;
323 k = md_block_size * num_starting_blocks;
324 }
325
326 bits = 8 * mac_end_offset;
327 if (!is_sslv3) {
328 /*
329 * Compute the initial HMAC block. For SSLv3, the padding and secret
330 * bytes are included in |header| because they take more than a
331 * single block.
332 */
333 bits += 8 * md_block_size;
334 memset(hmac_pad, 0, md_block_size);
335 if (!ossl_assert(mac_secret_length <= sizeof(hmac_pad)))
336 return 0;
337 memcpy(hmac_pad, mac_secret, mac_secret_length);
338 for (i = 0; i < md_block_size; i++)
339 hmac_pad[i] ^= 0x36;
340
341 md_transform(md_state.c, hmac_pad);
342 }
343
344 if (length_is_big_endian) {
345 memset(length_bytes, 0, md_length_size - 4);
346 length_bytes[md_length_size - 4] = (unsigned char)(bits >> 24);
347 length_bytes[md_length_size - 3] = (unsigned char)(bits >> 16);
348 length_bytes[md_length_size - 2] = (unsigned char)(bits >> 8);
349 length_bytes[md_length_size - 1] = (unsigned char)bits;
350 } else {
351 memset(length_bytes, 0, md_length_size);
352 length_bytes[md_length_size - 5] = (unsigned char)(bits >> 24);
353 length_bytes[md_length_size - 6] = (unsigned char)(bits >> 16);
354 length_bytes[md_length_size - 7] = (unsigned char)(bits >> 8);
355 length_bytes[md_length_size - 8] = (unsigned char)bits;
356 }
357
358 if (k > 0) {
359 if (is_sslv3) {
360 size_t overhang;
361
362 /*
363 * The SSLv3 header is larger than a single block. overhang is
364 * the number of bytes beyond a single block that the header
365 * consumes: either 7 bytes (SHA1) or 11 bytes (MD5). There are no
366 * ciphersuites in SSLv3 that are not SHA1 or MD5 based and
367 * therefore we can be confident that the header_length will be
368 * greater than |md_block_size|. However we add a sanity check just
369 * in case
370 */
371 if (header_length <= md_block_size) {
372 /* Should never happen */
373 return 0;
374 }
375 overhang = header_length - md_block_size;
376 md_transform(md_state.c, header);
377 memcpy(first_block, header + md_block_size, overhang);
378 memcpy(first_block + overhang, data, md_block_size - overhang);
379 md_transform(md_state.c, first_block);
380 for (i = 1; i < k / md_block_size - 1; i++)
381 md_transform(md_state.c, data + md_block_size * i - overhang);
382 } else {
383 /* k is a multiple of md_block_size. */
384 memcpy(first_block, header, 13);
385 memcpy(first_block + 13, data, md_block_size - 13);
386 md_transform(md_state.c, first_block);
387 for (i = 1; i < k / md_block_size; i++)
388 md_transform(md_state.c, data + md_block_size * i - 13);
389 }
390 }
391
392 memset(mac_out, 0, sizeof(mac_out));
393
394 /*
395 * We now process the final hash blocks. For each block, we construct it
396 * in constant time. If the |i==index_a| then we'll include the 0x80
397 * bytes and zero pad etc. For each block we selectively copy it, in
398 * constant time, to |mac_out|.
399 */
400 for (i = num_starting_blocks; i <= num_starting_blocks + variance_blocks;
401 i++) {
402 unsigned char block[MAX_HASH_BLOCK_SIZE];
403 unsigned char is_block_a = constant_time_eq_8_s(i, index_a);
404 unsigned char is_block_b = constant_time_eq_8_s(i, index_b);
405
406 for (j = 0; j < md_block_size; j++) {
407 unsigned char b = 0, is_past_c, is_past_cp1;
408
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
459 if (EVP_DigestInit_ex(md_ctx, md, NULL /* engine */) <= 0)
460 goto err;
461 if (is_sslv3) {
462 /* We repurpose |hmac_pad| to contain the SSLv3 pad2 block. */
463 memset(hmac_pad, 0x5c, sslv3_pad_length);
464
465 if (EVP_DigestUpdate(md_ctx, mac_secret, mac_secret_length) <= 0
466 || EVP_DigestUpdate(md_ctx, hmac_pad, sslv3_pad_length) <= 0
467 || EVP_DigestUpdate(md_ctx, mac_out, md_size) <= 0)
468 goto err;
469 } else {
470 /* Complete the HMAC in the standard manner. */
471 for (i = 0; i < md_block_size; i++)
472 hmac_pad[i] ^= 0x6a;
473
474 if (EVP_DigestUpdate(md_ctx, hmac_pad, md_block_size) <= 0
475 || EVP_DigestUpdate(md_ctx, mac_out, md_size) <= 0)
476 goto err;
477 }
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
482 ret = 1;
483 err:
484 EVP_MD_CTX_free(md_ctx);
485 return ret;
486 }
487
