| /* |
| * Copyright 1995-2021 The OpenSSL Project Authors. All Rights Reserved. |
| * |
| * Licensed under the Apache License 2.0 (the "License"). You may not use |
| * this file except in compliance with the License. You can obtain a copy |
| * in the file LICENSE in the source distribution or at |
| * https://www.openssl.org/source/license.html |
| */ |
| |
| #include <openssl/rand.h> |
| #include <openssl/evp.h> |
| #include "internal/constant_time.h" |
| #include "internal/cryptlib.h" |
| |
| /* |
| * This file has no dependencies on the rest of libssl because it is shared |
| * with the providers. It contains functions for low level CBC TLS padding |
| * removal. Responsibility for this lies with the cipher implementations in the |
| * providers. However there are legacy code paths in libssl which also need to |
| * do this. In time those legacy code paths can be removed and this file can be |
| * moved out of libssl. |
| */ |
| |
| static int ssl3_cbc_copy_mac(size_t *reclen, |
| size_t origreclen, |
| unsigned char *recdata, |
| unsigned char **mac, |
| int *alloced, |
| size_t block_size, |
| size_t mac_size, |
| size_t good, |
| OSSL_LIB_CTX *libctx); |
| |
| int ssl3_cbc_remove_padding_and_mac(size_t *reclen, |
| size_t origreclen, |
| unsigned char *recdata, |
| unsigned char **mac, |
| int *alloced, |
| size_t block_size, size_t mac_size, |
| OSSL_LIB_CTX *libctx); |
| |
| int tls1_cbc_remove_padding_and_mac(size_t *reclen, |
| size_t origreclen, |
| unsigned char *recdata, |
| unsigned char **mac, |
| int *alloced, |
| size_t block_size, size_t mac_size, |
| int aead, |
| OSSL_LIB_CTX *libctx); |
| |
| /*- |
| * ssl3_cbc_remove_padding removes padding from the decrypted, SSLv3, CBC |
| * record in |recdata| by updating |reclen| in constant time. It also extracts |
| * the MAC from the underlying record and places a pointer to it in |mac|. The |
| * MAC data can either be newly allocated memory, or a pointer inside the |
| * |recdata| buffer. If allocated then |*alloced| is set to 1, otherwise it is |
| * set to 0. |
| * |
| * origreclen: the original record length before any changes were made |
| * block_size: the block size of the cipher used to encrypt the record. |
| * mac_size: the size of the MAC to be extracted |
| * aead: 1 if an AEAD cipher is in use, or 0 otherwise |
| * returns: |
| * 0: if the record is publicly invalid. |
| * 1: if the record is publicly valid. If the padding removal fails then the |
| * MAC returned is random. |
| */ |
| int ssl3_cbc_remove_padding_and_mac(size_t *reclen, |
| size_t origreclen, |
| unsigned char *recdata, |
| unsigned char **mac, |
| int *alloced, |
| size_t block_size, size_t mac_size, |
| OSSL_LIB_CTX *libctx) |
| { |
| size_t padding_length; |
| size_t good; |
| const size_t overhead = 1 /* padding length byte */ + mac_size; |
| |
| /* |
| * These lengths are all public so we can test them in non-constant time. |
| */ |
| if (overhead > *reclen) |
| return 0; |
| |
| padding_length = recdata[*reclen - 1]; |
| good = constant_time_ge_s(*reclen, padding_length + overhead); |
| /* SSLv3 requires that the padding is minimal. */ |
| good &= constant_time_ge_s(block_size, padding_length + 1); |
| *reclen -= good & (padding_length + 1); |
| |
| return ssl3_cbc_copy_mac(reclen, origreclen, recdata, mac, alloced, |
| block_size, mac_size, good, libctx); |
| } |
| |
| /*- |
| * tls1_cbc_remove_padding_and_mac removes padding from the decrypted, TLS, CBC |
| * record in |recdata| by updating |reclen| in constant time. It also extracts |
| * the MAC from the underlying record and places a pointer to it in |mac|. The |
| * MAC data can either be newly allocated memory, or a pointer inside the |
| * |recdata| buffer. If allocated then |*alloced| is set to 1, otherwise it is |
| * set to 0. |
| * |
| * origreclen: the original record length before any changes were made |
| * block_size: the block size of the cipher used to encrypt the record. |
| * mac_size: the size of the MAC to be extracted |
| * aead: 1 if an AEAD cipher is in use, or 0 otherwise |
| * returns: |
| * 0: if the record is publicly invalid. |
| * 1: if the record is publicly valid. If the padding removal fails then the |
| * MAC returned is random. |
| */ |
| int tls1_cbc_remove_padding_and_mac(size_t *reclen, |
| size_t origreclen, |
| unsigned char *recdata, |
| unsigned char **mac, |
| int *alloced, |
| size_t block_size, size_t mac_size, |
| int aead, |
| OSSL_LIB_CTX *libctx) |
| { |
| size_t good = -1; |
| size_t padding_length, to_check, i; |
| size_t overhead = ((block_size == 1) ? 0 : 1) /* padding length byte */ |
| + mac_size; |
| |
| /* |
| * These lengths are all public so we can test them in non-constant |
| * time. |
| */ |
| if (overhead > *reclen) |
| return 0; |
| |
| if (block_size != 1) { |
| |
| padding_length = recdata[*reclen - 1]; |
| |
| if (aead) { |
| /* padding is already verified and we don't need to check the MAC */ |
| *reclen -= padding_length + 1 + mac_size; |
| return 1; |
| } |
| |
| good = constant_time_ge_s(*reclen, 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 > *reclen) |
| to_check = *reclen; |
| |
| for (i = 0; i < to_check; i++) { |
| unsigned char mask = constant_time_ge_8_s(padding_length, i); |
| unsigned char b = recdata[*reclen - 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. |
| */ |
| good = constant_time_eq_s(0xff, good & 0xff); |
| *reclen -= good & (padding_length + 1); |
| } |
| |
| return ssl3_cbc_copy_mac(reclen, origreclen, recdata, mac, alloced, |
| block_size, mac_size, good, libctx); |
| } |
| |
| /*- |
| * ssl3_cbc_copy_mac copies |md_size| bytes from the end of the record in |
| * |recdata| to |*mac| in constant time (independent of the concrete value of |
| * the record length |reclen|, which may vary within a 256-byte window). |
| * |
| * On entry: |
| * origreclen >= mac_size |
| * mac_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 |
| |
| static int ssl3_cbc_copy_mac(size_t *reclen, |
| size_t origreclen, |
| unsigned char *recdata, |
| unsigned char **mac, |
| int *alloced, |
| size_t block_size, |
| size_t mac_size, |
| size_t good, |
| OSSL_LIB_CTX *libctx) |
| { |
| #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 |
| unsigned char randmac[EVP_MAX_MD_SIZE]; |
| unsigned char *out; |
| |
| /* |
| * mac_end is the index of |recdata| just after the end of the MAC. |
| */ |
| size_t mac_end = *reclen; |
| size_t mac_start = mac_end - mac_size; |
| size_t in_mac; |
| /* |
| * scan_start contains the number of bytes that we can ignore because the |
| * MAC's position can only vary by 255 bytes. |
| */ |
| size_t scan_start = 0; |
| size_t i, j; |
| size_t rotate_offset; |
| |
| if (!ossl_assert(origreclen >= mac_size |
| && mac_size <= EVP_MAX_MD_SIZE)) |
| return 0; |
| |
| /* If no MAC then nothing to be done */ |
| if (mac_size == 0) { |
| /* No MAC so we can do this in non-constant time */ |
| if (good == 0) |
| return 0; |
| return 1; |
| } |
| |
| *reclen -= mac_size; |
| |
| if (block_size == 1) { |
| /* There's no padding so the position of the MAC is fixed */ |
| if (mac != NULL) |
| *mac = &recdata[*reclen]; |
| if (alloced != NULL) |
| *alloced = 0; |
| return 1; |
| } |
| |
| /* Create the random MAC we will emit if padding is bad */ |
| if (RAND_bytes_ex(libctx, randmac, mac_size, 0) <= 0) |
| return 0; |
| |
| if (!ossl_assert(mac != NULL && alloced != NULL)) |
| return 0; |
| *mac = out = OPENSSL_malloc(mac_size); |
| if (*mac == NULL) |
| return 0; |
| *alloced = 1; |
| |
| #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 (origreclen > mac_size + 255 + 1) |
| scan_start = origreclen - (mac_size + 255 + 1); |
| |
| in_mac = 0; |
| rotate_offset = 0; |
| memset(rotated_mac, 0, mac_size); |
| for (i = scan_start, j = 0; i < origreclen; i++) { |
| size_t mac_started = constant_time_eq_s(i, mac_start); |
| size_t mac_ended = constant_time_lt_s(i, mac_end); |
| unsigned char b = recdata[i]; |
| |
| in_mac |= mac_started; |
| in_mac &= mac_ended; |
| rotate_offset |= j & mac_started; |
| rotated_mac[j++] |= b & in_mac; |
| j &= constant_time_lt_s(j, mac_size); |
| } |
| |
| /* Now rotate the MAC */ |
| #if defined(CBC_MAC_ROTATE_IN_PLACE) |
| j = 0; |
| for (i = 0; i < mac_size; i++) { |
| /* in case cache-line is 32 bytes, touch second line */ |
| ((volatile unsigned char *)rotated_mac)[rotate_offset ^ 32]; |
| |
| /* If the padding wasn't good we emit a random MAC */ |
| out[j++] = constant_time_select_8((unsigned char)(good & 0xff), |
| rotated_mac[rotate_offset++], |
| randmac[i]); |
| rotate_offset &= constant_time_lt_s(rotate_offset, mac_size); |
| } |
| #else |
| memset(out, 0, mac_size); |
| rotate_offset = mac_size - rotate_offset; |
| rotate_offset &= constant_time_lt_s(rotate_offset, mac_size); |
| for (i = 0; i < mac_size; i++) { |
| for (j = 0; j < mac_size; j++) |
| out[j] |= rotated_mac[i] & constant_time_eq_8_s(j, rotate_offset); |
| rotate_offset++; |
| rotate_offset &= constant_time_lt_s(rotate_offset, mac_size); |
| |
| /* If the padding wasn't good we emit a random MAC */ |
| out[i] = constant_time_select_8((unsigned char)(good & 0xff), out[i], |
| randmac[i]); |
| } |
| #endif |
| |
| return 1; |
| } |
