/* $OpenBSD: s3_cbc.c,v 1.26 2022/11/26 16:08:55 tb Exp $ */ /* ==================================================================== * Copyright (c) 2012 The OpenSSL Project. All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * * 3. All advertising materials mentioning features or use of this * software must display the following acknowledgment: * "This product includes software developed by the OpenSSL Project * for use in the OpenSSL Toolkit. (http://www.openssl.org/)" * * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to * endorse or promote products derived from this software without * prior written permission. For written permission, please contact * openssl-core@openssl.org. * * 5. Products derived from this software may not be called "OpenSSL" * nor may "OpenSSL" appear in their names without prior written * permission of the OpenSSL Project. * * 6. Redistributions of any form whatsoever must retain the following * acknowledgment: * "This product includes software developed by the OpenSSL Project * for use in the OpenSSL Toolkit (http://www.openssl.org/)" * * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED * OF THE POSSIBILITY OF SUCH DAMAGE. * ==================================================================== * * This product includes cryptographic software written by Eric Young * (eay@cryptsoft.com). This product includes software written by Tim * Hudson (tjh@cryptsoft.com). * */ #include <openssl/md5.h> #include <openssl/sha.h> #include "ssl_local.h" /* MAX_HASH_BIT_COUNT_BYTES is the maximum number of bytes in the hash's length * field. (SHA-384/512 have 128-bit length.) */ #define MAX_HASH_BIT_COUNT_BYTES 16 /* MAX_HASH_BLOCK_SIZE is the maximum hash block size that we'll support. * Currently SHA-384/512 has a 128-byte block size and that's the largest * supported by TLS.) */ #define MAX_HASH_BLOCK_SIZE 128 /* Some utility functions are needed: * * These macros return the given value with the MSB copied to all the other * bits. They use the fact that arithmetic shift shifts-in the sign bit. * However, this is not ensured by the C standard so you may need to replace * them with something else on odd CPUs. */ #define DUPLICATE_MSB_TO_ALL(x) ((unsigned int)((int)(x) >> (sizeof(int) * 8 - 1))) #define DUPLICATE_MSB_TO_ALL_8(x) ((unsigned char)(DUPLICATE_MSB_TO_ALL(x))) /* constant_time_lt returns 0xff if a<b and 0x00 otherwise. */ static unsigned int constant_time_lt(unsigned int a, unsigned int b) { a -= b; return DUPLICATE_MSB_TO_ALL(a); } /* constant_time_ge returns 0xff if a>=b and 0x00 otherwise. */ static unsigned int constant_time_ge(unsigned int a, unsigned int b) { a -= b; return DUPLICATE_MSB_TO_ALL(~a); } /* constant_time_eq_8 returns 0xff if a==b and 0x00 otherwise. */ static unsigned char constant_time_eq_8(unsigned int a, unsigned int b) { unsigned int c = a ^ b; c--; return DUPLICATE_MSB_TO_ALL_8(c); } /* ssl3_cbc_remove_padding removes the CBC padding from the decrypted, TLS, CBC * record in |rec| in constant time and returns 1 if the padding is valid and * -1 otherwise. It also removes any explicit IV from the start of the record * without leaking any timing about whether there was enough space after the * padding was removed. * * block_size: the block size of the cipher used to encrypt the record. * returns: * 0: (in non-constant time) if the record is publicly invalid. * 1: if the padding was valid * -1: otherwise. */ int ssl3_cbc_remove_padding(SSL3_RECORD_INTERNAL *rec, unsigned int eiv_len, unsigned int mac_size) { unsigned int padding_length, good, to_check, i; const unsigned int overhead = 1 /* padding length byte */ + mac_size; /* * These lengths are all public so we can test them in * non-constant time. */ if (overhead + eiv_len > rec->length) return 0; /* We can now safely skip explicit IV, if any. */ rec->data += eiv_len; rec->input += eiv_len; rec->length -= eiv_len; padding_length = rec->data[rec->length - 1]; good = constant_time_ge(rec->length, overhead + padding_length); /* The padding consists of a length byte at the end of the record and * then that many bytes of padding, all with the same value as the * length byte. Thus, with the length byte included, there are i+1 * bytes of padding. * * We can't check just |padding_length+1| bytes because that leaks * decrypted information. Therefore we always have to check the maximum * amount of padding possible. (Again, the length of the record is * public information so we can use it.) */ to_check = 256; /* maximum amount of padding, inc length byte. */ if (to_check > rec->length) to_check = rec->length; for (i = 0; i < to_check; i++) { unsigned char mask = constant_time_ge(padding_length, i); unsigned char b = rec->data[rec->length - 1 - i]; /* The final |padding_length+1| bytes should all have the value * |padding_length|. Therefore the XOR should be zero. */ good &= ~(mask&(padding_length ^ b)); } /* If any of the final |padding_length+1| bytes had the wrong value, * one or more of the lower eight bits of |good| will be cleared. We * AND the bottom 8 bits together and duplicate the result to all the * bits. */ good &= good >> 4; good &= good >> 2; good &= good >> 1; good <<= sizeof(good)*8 - 1; good = DUPLICATE_MSB_TO_ALL(good); padding_length = good & (padding_length + 1); rec->length -= padding_length; rec->padding_length = padding_length; return (int)((good & 1) | (~good & -1)); } /* ssl3_cbc_copy_mac copies |md_size| bytes from the end of |rec| to |out| in * constant time (independent of the concrete value of rec->length, which may * vary within a 256-byte window). * * ssl3_cbc_remove_padding or tls1_cbc_remove_padding must be called prior to * this function. * * On entry: * rec->orig_len >= md_size * md_size <= EVP_MAX_MD_SIZE * * If CBC_MAC_ROTATE_IN_PLACE is defined then the rotation is performed with * variable accesses in a 64-byte-aligned buffer. Assuming that this fits into * a single or pair of cache-lines, then the variable memory accesses don't * actually affect the timing. CPUs with smaller cache-lines [if any] are * not multi-core and are not considered vulnerable to cache-timing attacks. */ #define CBC_MAC_ROTATE_IN_PLACE void ssl3_cbc_copy_mac(unsigned char* out, const SSL3_RECORD_INTERNAL *rec, unsigned int md_size, unsigned int orig_len) { #if defined(CBC_MAC_ROTATE_IN_PLACE) unsigned char rotated_mac_buf[64 + EVP_MAX_MD_SIZE]; unsigned char *rotated_mac; #else unsigned char rotated_mac[EVP_MAX_MD_SIZE]; #endif /* mac_end is the index of |rec->data| just after the end of the MAC. */ unsigned int mac_end = rec->length; unsigned int mac_start = mac_end - md_size; /* scan_start contains the number of bytes that we can ignore because * the MAC's position can only vary by 255 bytes. */ unsigned int scan_start = 0; unsigned int i, j; unsigned int div_spoiler; unsigned int rotate_offset; OPENSSL_assert(orig_len >= md_size); OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE); #if defined(CBC_MAC_ROTATE_IN_PLACE) rotated_mac = rotated_mac_buf + ((0 - (size_t)rotated_mac_buf)&63); #endif /* This information is public so it's safe to branch based on it. */ if (orig_len > md_size + 255 + 1) scan_start = orig_len - (md_size + 255 + 1); /* div_spoiler contains a multiple of md_size that is used to cause the * modulo operation to be constant time. Without this, the time varies * based on the amount of padding when running on Intel chips at least. * * The aim of right-shifting md_size is so that the compiler doesn't * figure out that it can remove div_spoiler as that would require it * to prove that md_size is always even, which I hope is beyond it. */ div_spoiler = md_size >> 1; div_spoiler <<= (sizeof(div_spoiler) - 1) * 8; rotate_offset = (div_spoiler + mac_start - scan_start) % md_size; memset(rotated_mac, 0, md_size); for (i = scan_start, j = 0; i < orig_len; i++) { unsigned char mac_started = constant_time_ge(i, mac_start); unsigned char mac_ended = constant_time_ge(i, mac_end); unsigned char b = rec->data[i]; rotated_mac[j++] |= b & mac_started & ~mac_ended; j &= constant_time_lt(j, md_size); } /* Now rotate the MAC */ #if defined(CBC_MAC_ROTATE_IN_PLACE) j = 0; for (i = 0; i < md_size; i++) { /* in case cache-line is 32 bytes, touch second line */ ((volatile unsigned char *)rotated_mac)[rotate_offset^32]; out[j++] = rotated_mac[rotate_offset++]; rotate_offset &= constant_time_lt(rotate_offset, md_size); } #else memset(out, 0, md_size); rotate_offset = md_size - rotate_offset; rotate_offset &= constant_time_lt(rotate_offset, md_size); for (i = 0; i < md_size; i++) { for (j = 0; j < md_size; j++) out[j] |= rotated_mac[i] & constant_time_eq_8(j, rotate_offset); rotate_offset++; rotate_offset &= constant_time_lt(rotate_offset, md_size); } #endif } #define l2n(l,c) (*((c)++)=(unsigned char)(((l)>>24)&0xff), \ *((c)++)=(unsigned char)(((l)>>16)&0xff), \ *((c)++)=(unsigned char)(((l)>> 8)&0xff), \ *((c)++)=(unsigned char)(((l) )&0xff)) #define l2n8(l,c) (*((c)++)=(unsigned char)(((l)>>56)&0xff), \ *((c)++)=(unsigned char)(((l)>>48)&0xff), \ *((c)++)=(unsigned char)(((l)>>40)&0xff), \ *((c)++)=(unsigned char)(((l)>>32)&0xff), \ *((c)++)=(unsigned char)(((l)>>24)&0xff), \ *((c)++)=(unsigned char)(((l)>>16)&0xff), \ *((c)++)=(unsigned char)(((l)>> 8)&0xff), \ *((c)++)=(unsigned char)(((l) )&0xff)) /* u32toLE serialises an unsigned, 32-bit number (n) as four bytes at (p) in * little-endian order. The value of p is advanced by four. */ #define u32toLE(n, p) \ (*((p)++)=(unsigned char)(n), \ *((p)++)=(unsigned char)(n>>8), \ *((p)++)=(unsigned char)(n>>16), \ *((p)++)=(unsigned char)(n>>24)) /* These functions serialize the state of a hash and thus perform the standard * "final" operation without adding the padding and length that such a function * typically does. */ static void tls1_md5_final_raw(void* ctx, unsigned char *md_out) { MD5_CTX *md5 = ctx; u32toLE(md5->A, md_out); u32toLE(md5->B, md_out); u32toLE(md5->C, md_out); u32toLE(md5->D, md_out); } static void tls1_sha1_final_raw(void* ctx, unsigned char *md_out) { SHA_CTX *sha1 = ctx; l2n(sha1->h0, md_out); l2n(sha1->h1, md_out); l2n(sha1->h2, md_out); l2n(sha1->h3, md_out); l2n(sha1->h4, md_out); } static void tls1_sha256_final_raw(void* ctx, unsigned char *md_out) { SHA256_CTX *sha256 = ctx; unsigned int i; for (i = 0; i < 8; i++) { l2n(sha256->h[i], md_out); } } static void tls1_sha512_final_raw(void* ctx, unsigned char *md_out) { SHA512_CTX *sha512 = ctx; unsigned int i; for (i = 0; i < 8; i++) { l2n8(sha512->h[i], md_out); } } /* Largest hash context ever used by the functions above. */ #define LARGEST_DIGEST_CTX SHA512_CTX /* Type giving the alignment needed by the above */ #define LARGEST_DIGEST_CTX_ALIGNMENT SHA_LONG64 /* ssl3_cbc_record_digest_supported returns 1 iff |ctx| uses a hash function * which ssl3_cbc_digest_record supports. */ char ssl3_cbc_record_digest_supported(const EVP_MD_CTX *ctx) { switch (EVP_MD_CTX_type(ctx)) { case NID_md5: case NID_sha1: case NID_sha224: case NID_sha256: case NID_sha384: case NID_sha512: return 1; default: return 0; } } /* ssl3_cbc_digest_record computes the MAC of a decrypted, padded TLS * record. * * ctx: the EVP_MD_CTX from which we take the hash function. * ssl3_cbc_record_digest_supported must return true for this EVP_MD_CTX. * md_out: the digest output. At most EVP_MAX_MD_SIZE bytes will be written. * md_out_size: if non-NULL, the number of output bytes is written here. * header: the 13-byte, TLS record header. * data: the record data itself, less any preceeding explicit IV. * data_plus_mac_size: the secret, reported length of the data and MAC * once the padding has been removed. * data_plus_mac_plus_padding_size: the public length of the whole * record, including padding. * * On entry: by virtue of having been through one of the remove_padding * functions, above, we know that data_plus_mac_size is large enough to contain * a padding byte and MAC. (If the padding was invalid, it might contain the * padding too. ) */ int ssl3_cbc_digest_record(const EVP_MD_CTX *ctx, unsigned char* md_out, size_t* md_out_size, const unsigned char header[13], const unsigned char *data, size_t data_plus_mac_size, size_t data_plus_mac_plus_padding_size, const unsigned char *mac_secret, unsigned int mac_secret_length) { union { /* * Alignment here is to allow this to be cast as SHA512_CTX * without losing alignment required by the 64-bit SHA_LONG64 * integer it contains. */ LARGEST_DIGEST_CTX_ALIGNMENT align; unsigned char c[sizeof(LARGEST_DIGEST_CTX)]; } md_state; void (*md_final_raw)(void *ctx, unsigned char *md_out); void (*md_transform)(void *ctx, const unsigned char *block); unsigned int md_size, md_block_size = 64; unsigned int header_length, variance_blocks, len, max_mac_bytes, num_blocks, num_starting_blocks, k, mac_end_offset, c, index_a, index_b; unsigned int bits; /* at most 18 bits */ unsigned char length_bytes[MAX_HASH_BIT_COUNT_BYTES]; /* hmac_pad is the masked HMAC key. */ unsigned char hmac_pad[MAX_HASH_BLOCK_SIZE]; unsigned char first_block[MAX_HASH_BLOCK_SIZE]; unsigned char mac_out[EVP_MAX_MD_SIZE]; unsigned int i, j, md_out_size_u; EVP_MD_CTX *md_ctx; /* mdLengthSize is the number of bytes in the length field that terminates * the hash. */ unsigned int md_length_size = 8; char length_is_big_endian = 1; /* This is a, hopefully redundant, check that allows us to forget about * many possible overflows later in this function. */ OPENSSL_assert(data_plus_mac_plus_padding_size < 1024*1024); switch (EVP_MD_CTX_type(ctx)) { case NID_md5: MD5_Init((MD5_CTX*)md_state.c); md_final_raw = tls1_md5_final_raw; md_transform = (void(*)(void *ctx, const unsigned char *block)) MD5_Transform; md_size = 16; length_is_big_endian = 0; break; case NID_sha1: SHA1_Init((SHA_CTX*)md_state.c); md_final_raw = tls1_sha1_final_raw; md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA1_Transform; md_size = 20; break; case NID_sha224: SHA224_Init((SHA256_CTX*)md_state.c); md_final_raw = tls1_sha256_final_raw; md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA256_Transform; md_size = 224/8; break; case NID_sha256: SHA256_Init((SHA256_CTX*)md_state.c); md_final_raw = tls1_sha256_final_raw; md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA256_Transform; md_size = 32; break; case NID_sha384: SHA384_Init((SHA512_CTX*)md_state.c); md_final_raw = tls1_sha512_final_raw; md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA512_Transform; md_size = 384/8; md_block_size = 128; md_length_size = 16; break; case NID_sha512: SHA512_Init((SHA512_CTX*)md_state.c); md_final_raw = tls1_sha512_final_raw; md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA512_Transform; md_size = 64; md_block_size = 128; md_length_size = 16; break; default: /* ssl3_cbc_record_digest_supported should have been * called first to check that the hash function is * supported. */ OPENSSL_assert(0); if (md_out_size) *md_out_size = 0; return 0; } OPENSSL_assert(md_length_size <= MAX_HASH_BIT_COUNT_BYTES); OPENSSL_assert(md_block_size <= MAX_HASH_BLOCK_SIZE); OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE); header_length = 13; /* variance_blocks is the number of blocks of the hash that we have to * calculate in constant time because they could be altered by the * padding value. * * TLSv1 has MACs up to 48 bytes long (SHA-384) and the padding is not * required to be minimal. Therefore we say that the final six blocks * can vary based on the padding. * * Later in the function, if the message is short and there obviously * cannot be this many blocks then variance_blocks can be reduced. */ variance_blocks = 6; /* From now on we're dealing with the MAC, which conceptually has 13 * bytes of `header' before the start of the data (TLS) */ len = data_plus_mac_plus_padding_size + header_length; /* max_mac_bytes contains the maximum bytes of bytes in the MAC, including * |header|, assuming that there's no padding. */ max_mac_bytes = len - md_size - 1; /* num_blocks is the maximum number of hash blocks. */ num_blocks = (max_mac_bytes + 1 + md_length_size + md_block_size - 1) / md_block_size; /* In order to calculate the MAC in constant time we have to handle * the final blocks specially because the padding value could cause the * end to appear somewhere in the final |variance_blocks| blocks and we * can't leak where. However, |num_starting_blocks| worth of data can * be hashed right away because no padding value can affect whether * they are plaintext. */ num_starting_blocks = 0; /* k is the starting byte offset into the conceptual header||data where * we start processing. */ k = 0; /* mac_end_offset is the index just past the end of the data to be * MACed. */ mac_end_offset = data_plus_mac_size + header_length - md_size; /* c is the index of the 0x80 byte in the final hash block that * contains application data. */ c = mac_end_offset % md_block_size; /* index_a is the hash block number that contains the 0x80 terminating * value. */ index_a = mac_end_offset / md_block_size; /* index_b is the hash block number that contains the 64-bit hash * length, in bits. */ index_b = (mac_end_offset + md_length_size) / md_block_size; /* bits is the hash-length in bits. It includes the additional hash * block for the masked HMAC key. */ if (num_blocks > variance_blocks) { num_starting_blocks = num_blocks - variance_blocks; k = md_block_size*num_starting_blocks; } bits = 8*mac_end_offset; /* Compute the initial HMAC block. */ bits += 8*md_block_size; memset(hmac_pad, 0, md_block_size); OPENSSL_assert(mac_secret_length <= sizeof(hmac_pad)); memcpy(hmac_pad, mac_secret, mac_secret_length); for (i = 0; i < md_block_size; i++) hmac_pad[i] ^= 0x36; md_transform(md_state.c, hmac_pad); if (length_is_big_endian) { memset(length_bytes, 0, md_length_size - 4); length_bytes[md_length_size - 4] = (unsigned char)(bits >> 24); length_bytes[md_length_size - 3] = (unsigned char)(bits >> 16); length_bytes[md_length_size - 2] = (unsigned char)(bits >> 8); length_bytes[md_length_size - 1] = (unsigned char)bits; } else { memset(length_bytes, 0, md_length_size); length_bytes[md_length_size - 5] = (unsigned char)(bits >> 24); length_bytes[md_length_size - 6] = (unsigned char)(bits >> 16); length_bytes[md_length_size - 7] = (unsigned char)(bits >> 8); length_bytes[md_length_size - 8] = (unsigned char)bits; } if (k > 0) { /* k is a multiple of md_block_size. */ memcpy(first_block, header, 13); memcpy(first_block + 13, data, md_block_size - 13); md_transform(md_state.c, first_block); for (i = 1; i < k/md_block_size; i++) md_transform(md_state.c, data + md_block_size*i - 13); } memset(mac_out, 0, sizeof(mac_out)); /* We now process the final hash blocks. For each block, we construct * it in constant time. If the |i==index_a| then we'll include the 0x80 * bytes and zero pad etc. For each block we selectively copy it, in * constant time, to |mac_out|. */ for (i = num_starting_blocks; i <= num_starting_blocks + variance_blocks; i++) { unsigned char block[MAX_HASH_BLOCK_SIZE]; unsigned char is_block_a = constant_time_eq_8(i, index_a); unsigned char is_block_b = constant_time_eq_8(i, index_b); for (j = 0; j < md_block_size; j++) { unsigned char b = 0, is_past_c, is_past_cp1; if (k < header_length) b = header[k]; else if (k < data_plus_mac_plus_padding_size + header_length) b = data[k - header_length]; k++; is_past_c = is_block_a & constant_time_ge(j, c); is_past_cp1 = is_block_a & constant_time_ge(j, c + 1); /* If this is the block containing the end of the * application data, and we are at the offset for the * 0x80 value, then overwrite b with 0x80. */ b = (b&~is_past_c) | (0x80&is_past_c); /* If this is the block containing the end of the * application data and we're past the 0x80 value then * just write zero. */ b = b&~is_past_cp1; /* If this is index_b (the final block), but not * index_a (the end of the data), then the 64-bit * length didn't fit into index_a and we're having to * add an extra block of zeros. */ b &= ~is_block_b | is_block_a; /* The final bytes of one of the blocks contains the * length. */ if (j >= md_block_size - md_length_size) { /* If this is index_b, write a length byte. */ b = (b&~is_block_b) | (is_block_b&length_bytes[j - (md_block_size - md_length_size)]); } block[j] = b; } md_transform(md_state.c, block); md_final_raw(md_state.c, block); /* If this is index_b, copy the hash value to |mac_out|. */ for (j = 0; j < md_size; j++) mac_out[j] |= block[j]&is_block_b; } if ((md_ctx = EVP_MD_CTX_new()) == NULL) return 0; if (!EVP_DigestInit_ex(md_ctx, EVP_MD_CTX_md(ctx), NULL /* engine */)) { EVP_MD_CTX_free(md_ctx); return 0; } /* Complete the HMAC in the standard manner. */ for (i = 0; i < md_block_size; i++) hmac_pad[i] ^= 0x6a; EVP_DigestUpdate(md_ctx, hmac_pad, md_block_size); EVP_DigestUpdate(md_ctx, mac_out, md_size); EVP_DigestFinal(md_ctx, md_out, &md_out_size_u); if (md_out_size) *md_out_size = md_out_size_u; EVP_MD_CTX_free(md_ctx); return 1; }
