2 * Copyright 2012-2016 The OpenSSL Project Authors. All Rights Reserved.
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
10 #include "internal/constant_time_locl.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 six blocks can
260 * vary based on the padding. Later in the function, if the message is
261 * short and there obviously cannot be this many blocks then
262 * variance_blocks can be reduced.
264 variance_blocks = is_sslv3 ? 2 : 6;
266 * From now on we're dealing with the MAC, which conceptually has 13
267 * bytes of `header' before the start of the data (TLS) or 71/75 bytes
270 len = data_plus_mac_plus_padding_size + header_length;
272 * max_mac_bytes contains the maximum bytes of bytes in the MAC,
273 * including * |header|, assuming that there's no padding.
275 max_mac_bytes = len - md_size - 1;
276 /* num_blocks is the maximum number of hash blocks. */
278 (max_mac_bytes + 1 + md_length_size + md_block_size -
281 * In order to calculate the MAC in constant time we have to handle the
282 * final blocks specially because the padding value could cause the end
283 * to appear somewhere in the final |variance_blocks| blocks and we can't
284 * leak where. However, |num_starting_blocks| worth of data can be hashed
285 * right away because no padding value can affect whether they are
288 num_starting_blocks = 0;
290 * k is the starting byte offset into the conceptual header||data where
291 * we start processing.
295 * mac_end_offset is the index just past the end of the data to be MACed.
297 mac_end_offset = data_plus_mac_size + header_length - md_size;
299 * c is the index of the 0x80 byte in the final hash block that contains
302 c = mac_end_offset % md_block_size;
304 * index_a is the hash block number that contains the 0x80 terminating
307 index_a = mac_end_offset / md_block_size;
309 * index_b is the hash block number that contains the 64-bit hash length,
312 index_b = (mac_end_offset + md_length_size) / md_block_size;
314 * bits is the hash-length in bits. It includes the additional hash block
315 * for the masked HMAC key, or whole of |header| in the case of SSLv3.
319 * For SSLv3, if we're going to have any starting blocks then we need at
320 * least two because the header is larger than a single block.
322 if (num_blocks > variance_blocks + (is_sslv3 ? 1 : 0)) {
323 num_starting_blocks = num_blocks - variance_blocks;
324 k = md_block_size * num_starting_blocks;
327 bits = 8 * mac_end_offset;
330 * Compute the initial HMAC block. For SSLv3, the padding and secret
331 * bytes are included in |header| because they take more than a
334 bits += 8 * md_block_size;
335 memset(hmac_pad, 0, md_block_size);
336 if (!ossl_assert(mac_secret_length <= sizeof(hmac_pad)))
338 memcpy(hmac_pad, mac_secret, mac_secret_length);
339 for (i = 0; i < md_block_size; i++)
342 md_transform(md_state.c, hmac_pad);
345 if (length_is_big_endian) {
346 memset(length_bytes, 0, md_length_size - 4);
347 length_bytes[md_length_size - 4] = (unsigned char)(bits >> 24);
348 length_bytes[md_length_size - 3] = (unsigned char)(bits >> 16);
349 length_bytes[md_length_size - 2] = (unsigned char)(bits >> 8);
350 length_bytes[md_length_size - 1] = (unsigned char)bits;
352 memset(length_bytes, 0, md_length_size);
353 length_bytes[md_length_size - 5] = (unsigned char)(bits >> 24);
354 length_bytes[md_length_size - 6] = (unsigned char)(bits >> 16);
355 length_bytes[md_length_size - 7] = (unsigned char)(bits >> 8);
356 length_bytes[md_length_size - 8] = (unsigned char)bits;
364 * The SSLv3 header is larger than a single block. overhang is
365 * the number of bytes beyond a single block that the header
366 * consumes: either 7 bytes (SHA1) or 11 bytes (MD5). There are no
367 * ciphersuites in SSLv3 that are not SHA1 or MD5 based and
368 * therefore we can be confident that the header_length will be
369 * greater than |md_block_size|. However we add a sanity check just
372 if (header_length <= md_block_size) {
373 /* Should never happen */
376 overhang = header_length - md_block_size;
377 md_transform(md_state.c, header);
378 memcpy(first_block, header + md_block_size, overhang);
379 memcpy(first_block + overhang, data, md_block_size - overhang);
380 md_transform(md_state.c, first_block);
381 for (i = 1; i < k / md_block_size - 1; i++)
382 md_transform(md_state.c, data + md_block_size * i - overhang);
384 /* k is a multiple of md_block_size. */
385 memcpy(first_block, header, 13);
386 memcpy(first_block + 13, data, md_block_size - 13);
387 md_transform(md_state.c, first_block);
388 for (i = 1; i < k / md_block_size; i++)
389 md_transform(md_state.c, data + md_block_size * i - 13);
393 memset(mac_out, 0, sizeof(mac_out));
396 * We now process the final hash blocks. For each block, we construct it
397 * in constant time. If the |i==index_a| then we'll include the 0x80
398 * bytes and zero pad etc. For each block we selectively copy it, in
399 * constant time, to |mac_out|.
401 for (i = num_starting_blocks; i <= num_starting_blocks + variance_blocks;
403 unsigned char block[MAX_HASH_BLOCK_SIZE];
404 unsigned char is_block_a = constant_time_eq_8_s(i, index_a);
405 unsigned char is_block_b = constant_time_eq_8_s(i, index_b);
406 for (j = 0; j < md_block_size; j++) {
407 unsigned char b = 0, is_past_c, is_past_cp1;
408 if (k < header_length)
410 else if (k < data_plus_mac_plus_padding_size + header_length)
411 b = data[k - header_length];
414 is_past_c = is_block_a & constant_time_ge_8_s(j, c);
415 is_past_cp1 = is_block_a & constant_time_ge_8_s(j, c + 1);
417 * If this is the block containing the end of the application
418 * data, and we are at the offset for the 0x80 value, then
419 * overwrite b with 0x80.
421 b = constant_time_select_8(is_past_c, 0x80, b);
423 * If this block contains the end of the application data
424 * and we're past the 0x80 value then just write zero.
426 b = b & ~is_past_cp1;
428 * If this is index_b (the final block), but not index_a (the end
429 * of the data), then the 64-bit length didn't fit into index_a
430 * and we're having to add an extra block of zeros.
432 b &= ~is_block_b | is_block_a;
435 * The final bytes of one of the blocks contains the length.
437 if (j >= md_block_size - md_length_size) {
438 /* If this is index_b, write a length byte. */
439 b = constant_time_select_8(is_block_b,
442 md_length_size)], b);
447 md_transform(md_state.c, block);
448 md_final_raw(md_state.c, block);
449 /* If this is index_b, copy the hash value to |mac_out|. */
450 for (j = 0; j < md_size; j++)
451 mac_out[j] |= block[j] & is_block_b;
454 md_ctx = EVP_MD_CTX_new();
457 if (EVP_DigestInit_ex(md_ctx, EVP_MD_CTX_md(ctx), NULL /* engine */ ) <= 0)
460 /* We repurpose |hmac_pad| to contain the SSLv3 pad2 block. */
461 memset(hmac_pad, 0x5c, sslv3_pad_length);
463 if (EVP_DigestUpdate(md_ctx, mac_secret, mac_secret_length) <= 0
464 || EVP_DigestUpdate(md_ctx, hmac_pad, sslv3_pad_length) <= 0
465 || EVP_DigestUpdate(md_ctx, mac_out, md_size) <= 0)
468 /* Complete the HMAC in the standard manner. */
469 for (i = 0; i < md_block_size; i++)
472 if (EVP_DigestUpdate(md_ctx, hmac_pad, md_block_size) <= 0
473 || EVP_DigestUpdate(md_ctx, mac_out, md_size) <= 0)
476 /* TODO(size_t): Convert me */
477 ret = EVP_DigestFinal(md_ctx, md_out, &md_out_size_u);
478 if (ret && md_out_size)
479 *md_out_size = md_out_size_u;
480 EVP_MD_CTX_free(md_ctx);
484 EVP_MD_CTX_free(md_ctx);