2 * Copyright 2012-2019 The OpenSSL Project Authors. All Rights Reserved.
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
10 #include "internal/constant_time.h"
11 #include "ssl_local.h"
12 #include "internal/cryptlib.h"
14 #include <openssl/md5.h>
15 #include <openssl/sha.h>
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.)
21 #define MAX_HASH_BIT_COUNT_BYTES 16
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
28 #define MAX_HASH_BLOCK_SIZE 128
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.
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))
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.
45 static void tls1_md5_final_raw(void *ctx
, unsigned char *md_out
)
48 u32toLE(md5
->A
, md_out
);
49 u32toLE(md5
->B
, md_out
);
50 u32toLE(md5
->C
, md_out
);
51 u32toLE(md5
->D
, md_out
);
54 static void tls1_sha1_final_raw(void *ctx
, unsigned char *md_out
)
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
);
64 static void tls1_sha256_final_raw(void *ctx
, unsigned char *md_out
)
66 SHA256_CTX
*sha256
= ctx
;
69 for (i
= 0; i
< 8; i
++) {
70 l2n(sha256
->h
[i
], md_out
);
74 static void tls1_sha512_final_raw(void *ctx
, unsigned char *md_out
)
76 SHA512_CTX
*sha512
= ctx
;
79 for (i
= 0; i
< 8; i
++) {
80 l2n8(sha512
->h
[i
], md_out
);
84 #undef LARGEST_DIGEST_CTX
85 #define LARGEST_DIGEST_CTX SHA512_CTX
88 * ssl3_cbc_record_digest_supported returns 1 iff |ctx| uses a hash function
89 * which ssl3_cbc_digest_record supports.
91 char ssl3_cbc_record_digest_supported(const EVP_MD_CTX
*ctx
)
93 switch (EVP_MD_CTX_type(ctx
)) {
107 * ssl3_cbc_digest_record computes the MAC of a decrypted, padded SSLv3/TLS
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.
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
126 * Returns 1 on success or 0 on error
128 int ssl3_cbc_digest_record(const EVP_MD_CTX
*ctx
,
129 unsigned char *md_out
,
131 const unsigned char header
[13],
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
)
140 unsigned char c
[sizeof(LARGEST_DIGEST_CTX
)];
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
];
155 unsigned md_out_size_u
;
156 EVP_MD_CTX
*md_ctx
= NULL
;
158 * mdLengthSize is the number of bytes in the length field that
159 * terminates * the hash.
161 size_t md_length_size
= 8;
162 char length_is_big_endian
= 1;
166 * This is a, hopefully redundant, check that allows us to forget about
167 * many possible overflows later in this function.
169 if (!ossl_assert(data_plus_mac_plus_padding_size
< 1024 * 1024))
172 switch (EVP_MD_CTX_type(ctx
)) {
174 if (MD5_Init((MD5_CTX
*)md_state
.c
) <= 0)
176 md_final_raw
= tls1_md5_final_raw
;
178 (void (*)(void *ctx
, const unsigned char *block
))MD5_Transform
;
180 sslv3_pad_length
= 48;
181 length_is_big_endian
= 0;
184 if (SHA1_Init((SHA_CTX
*)md_state
.c
) <= 0)
186 md_final_raw
= tls1_sha1_final_raw
;
188 (void (*)(void *ctx
, const unsigned char *block
))SHA1_Transform
;
192 if (SHA224_Init((SHA256_CTX
*)md_state
.c
) <= 0)
194 md_final_raw
= tls1_sha256_final_raw
;
196 (void (*)(void *ctx
, const unsigned char *block
))SHA256_Transform
;
200 if (SHA256_Init((SHA256_CTX
*)md_state
.c
) <= 0)
202 md_final_raw
= tls1_sha256_final_raw
;
204 (void (*)(void *ctx
, const unsigned char *block
))SHA256_Transform
;
208 if (SHA384_Init((SHA512_CTX
*)md_state
.c
) <= 0)
210 md_final_raw
= tls1_sha512_final_raw
;
212 (void (*)(void *ctx
, const unsigned char *block
))SHA512_Transform
;
218 if (SHA512_Init((SHA512_CTX
*)md_state
.c
) <= 0)
220 md_final_raw
= tls1_sha512_final_raw
;
222 (void (*)(void *ctx
, const unsigned char *block
))SHA512_Transform
;
229 * ssl3_cbc_record_digest_supported should have been called first to
230 * check that the hash function is supported.
232 if (md_out_size
!= NULL
)
234 return ossl_assert(0);
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
))
244 header_length
= mac_secret_length
+ sslv3_pad_length
+ 8 /* sequence
246 1 /* record type */ +
247 2 /* record length */ ;
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|
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.
265 variance_blocks
= is_sslv3
? 2 : ( ((255 + 1 + md_size
+ md_block_size
- 1) / md_block_size
) + 1);
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
271 len
= data_plus_mac_plus_padding_size
+ header_length
;
273 * max_mac_bytes contains the maximum bytes of bytes in the MAC,
274 * including * |header|, assuming that there's no padding.
276 max_mac_bytes
= len
- md_size
- 1;
277 /* num_blocks is the maximum number of hash blocks. */
279 (max_mac_bytes
+ 1 + md_length_size
+ md_block_size
-
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
289 num_starting_blocks
= 0;
291 * k is the starting byte offset into the conceptual header||data where
292 * we start processing.
296 * mac_end_offset is the index just past the end of the data to be MACed.
298 mac_end_offset
= data_plus_mac_size
+ header_length
- md_size
;
300 * c is the index of the 0x80 byte in the final hash block that contains
303 c
= mac_end_offset
% md_block_size
;
305 * index_a is the hash block number that contains the 0x80 terminating
308 index_a
= mac_end_offset
/ md_block_size
;
310 * index_b is the hash block number that contains the 64-bit hash length,
313 index_b
= (mac_end_offset
+ md_length_size
) / md_block_size
;
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.
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.
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
;
328 bits
= 8 * mac_end_offset
;
331 * Compute the initial HMAC block. For SSLv3, the padding and secret
332 * bytes are included in |header| because they take more than a
335 bits
+= 8 * md_block_size
;
336 memset(hmac_pad
, 0, md_block_size
);
337 if (!ossl_assert(mac_secret_length
<= sizeof(hmac_pad
)))
339 memcpy(hmac_pad
, mac_secret
, mac_secret_length
);
340 for (i
= 0; i
< md_block_size
; i
++)
343 md_transform(md_state
.c
, hmac_pad
);
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
;
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
;
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
373 if (header_length
<= md_block_size
) {
374 /* Should never happen */
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
);
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);
394 memset(mac_out
, 0, sizeof(mac_out
));
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|.
402 for (i
= num_starting_blocks
; i
<= num_starting_blocks
+ variance_blocks
;
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
)
411 else if (k
< data_plus_mac_plus_padding_size
+ header_length
)
412 b
= data
[k
- header_length
];
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);
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.
422 b
= constant_time_select_8(is_past_c
, 0x80, b
);
424 * If this block contains the end of the application data
425 * and we're past the 0x80 value then just write zero.
427 b
= b
& ~is_past_cp1
;
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.
433 b
&= ~is_block_b
| is_block_a
;
436 * The final bytes of one of the blocks contains the length.
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
,
443 md_length_size
)], b
);
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
;
455 md_ctx
= EVP_MD_CTX_new();
458 if (EVP_DigestInit_ex(md_ctx
, EVP_MD_CTX_md(ctx
), NULL
/* engine */ ) <= 0)
461 /* We repurpose |hmac_pad| to contain the SSLv3 pad2 block. */
462 memset(hmac_pad
, 0x5c, sslv3_pad_length
);
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)
469 /* Complete the HMAC in the standard manner. */
470 for (i
= 0; i
< md_block_size
; i
++)
473 if (EVP_DigestUpdate(md_ctx
, hmac_pad
, md_block_size
) <= 0
474 || EVP_DigestUpdate(md_ctx
, mac_out
, md_size
) <= 0)
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
);
485 EVP_MD_CTX_free(md_ctx
);