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/*
* Copyright (C) 2015 Freie Universitรคt Berlin
*
* This file is subject to the terms and conditions of the GNU Lesser
* General Public License v2.1. See the file LICENSE in the top level
* directory for more details.
*/
/**
* @ingroup sys_crypto_modes
* @{
*
* @file
* @brief Crypto mode - counter with CBC-MAC
*
* @author Nico von Geyso <nico.geyso@fu-berlin.de>
*
* @}
*/
#include <string.h>
#include "debug.h"
#include "crypto/helper.h"
#include "crypto/modes/ctr.h"
#include "crypto/modes/ccm.h"
static inline int min(int a, int b)
{
if (a < b) {
return a;
}
else {
return b;
}
}
int ccm_compute_cbc_mac(cipher_t* cipher, uint8_t iv[16],
uint8_t* input, size_t length, uint8_t* mac)
{
uint8_t offset, block_size, mac_enc[16] = {0};
block_size = cipher_get_block_size(cipher);
memmove(mac, iv, 16);
offset = 0;
do {
uint8_t block_size_input = (length - offset > block_size) ?
block_size : length - offset;
/* CBC-Mode: XOR plaintext with ciphertext of (n-1)-th block */
for (int i = 0; i < block_size_input; ++i) {
mac[i] ^= input[offset + i];
}
if (cipher_encrypt(cipher, mac, mac_enc) != 1) {
return CIPHER_ERR_ENC_FAILED;
}
memcpy(mac, mac_enc, block_size);
offset += block_size_input;
} while (offset < length);
return offset;
}
int ccm_create_mac_iv(cipher_t* cipher, uint8_t auth_data_len, uint8_t M,
uint8_t L, uint8_t* nonce, uint8_t nonce_len,
size_t plaintext_len, uint8_t X1[16])
{
uint8_t M_, L_;
/* ensure everything is set to zero */
memset(X1, 0, 16);
/* set flags in B[0] - bit format:
7 6 5..3 2..0
Reserved Adata M_ L_ */
M_ = (M - 2) / 2;
L_ = L - 1;
X1[0] = 64 * (auth_data_len > 0) + 8 * M_ + L_;
/* copy nonce to B[1..15-L] */
memcpy(&X1[1], nonce, min(nonce_len, 15 - L));
/* write plaintext_len to B[15..16-L] */
for (uint8_t i = 15; i > 16 - L; --i) {
X1[i] = plaintext_len & 0xff;
plaintext_len >>= 8;
}
/* if there is still data, plaintext_len was too big */
if (plaintext_len > 0) {
return CIPHER_ERR_INVALID_LENGTH;
}
if (cipher_encrypt(cipher, X1, X1) != 1) {
return CIPHER_ERR_ENC_FAILED;
}
return 0;
}
int ccm_compute_adata_mac(cipher_t* cipher, uint8_t* auth_data,
uint32_t auth_data_len, uint8_t X1[16])
{
if (auth_data_len > 0) {
int len;
/* 16 octet block size + max. 10 len encoding */
uint8_t auth_data_encoded[26], len_encoding = 0;
if ( auth_data_len < (((uint32_t) 2) << 16)) { /* length (0x0001 ... 0xFEFF) */
len_encoding = 2;
auth_data_encoded[1] = auth_data_len & 0xFF;
auth_data_encoded[0] = (auth_data_len >> 8) & 0xFF;
} else {
DEBUG("UNSUPPORTED Adata length\n");
return -1;
}
memcpy(auth_data_encoded + len_encoding, auth_data, auth_data_len);
len = ccm_compute_cbc_mac(cipher, X1, auth_data_encoded, auth_data_len + len_encoding, X1);
if (len < 0) {
return -1;
}
}
return 0;
}
int cipher_encrypt_ccm(cipher_t* cipher, uint8_t* auth_data, uint32_t auth_data_len,
uint8_t mac_length, uint8_t length_encoding,
uint8_t* nonce, size_t nonce_len,
uint8_t* input, size_t input_len,
uint8_t* output)
{
int len = -1;
uint32_t length_max;
uint8_t nonce_counter[16] = {0}, mac_iv[16] = {0}, mac[16] = {0},
stream_block[16] = {0}, zero_block[16] = {0}, block_size;
if (mac_length % 2 != 0 || mac_length < 4 || mac_length > 16) {
return CCM_ERR_INVALID_MAC_LENGTH;
}
length_max = 2 << (8 * length_encoding);
if (length_encoding < 2 || length_encoding > 8 ||
input_len - auth_data_len > length_max) {
return CCM_ERR_INVALID_LENGTH_ENCODING;
}
/* Create B0, encrypt it (X1) and use it as mac_iv */
block_size = cipher_get_block_size(cipher);
if (ccm_create_mac_iv(cipher, auth_data_len, mac_length, length_encoding,
nonce, nonce_len, input_len, mac_iv) < 0) {
return CCM_ERR_INVALID_DATA_LENGTH;
}
/* MAC calulation (T) with additional data and plaintext */
ccm_compute_adata_mac(cipher, auth_data, auth_data_len, mac_iv);
len = ccm_compute_cbc_mac(cipher, mac_iv, input, input_len, mac);
if (len < 0) {
return len;
}
/* Compute first stream block */
nonce_counter[0] = length_encoding - 1;
memcpy(&nonce_counter[1], nonce,
min(nonce_len, (size_t) 15 - length_encoding));
len = cipher_encrypt_ctr(cipher, nonce_counter, block_size,
zero_block, block_size, stream_block);
if (len < 0) {
return len;
}
/* Encrypt message in counter mode */
crypto_block_inc_ctr(nonce_counter, block_size - nonce_len);
len = cipher_encrypt_ctr(cipher, nonce_counter, nonce_len, input,
input_len, output);
if (len < 0) {
return len;
}
/* auth value: mac ^ first stream block */
for (uint8_t i = 0; i < mac_length; ++i) {
output[len + i] = mac[i] ^ stream_block[i];
}
return len + mac_length;
}
int cipher_decrypt_ccm(cipher_t* cipher, uint8_t* auth_data,
uint32_t auth_data_len, uint8_t mac_length,
uint8_t length_encoding, uint8_t* nonce, size_t nonce_len,
uint8_t* input, size_t input_len, uint8_t* plain)
{
int len = -1;
uint32_t length_max;
uint8_t nonce_counter[16] = {0}, mac_iv[16] = {0}, mac[16] = {0},
mac_recv[16] = {0}, stream_block[16] = {0}, zero_block[16] = {0},
plain_len, block_size;
if (mac_length % 2 != 0 || mac_length < 4 || mac_length > 16) {
return CCM_ERR_INVALID_MAC_LENGTH;
}
length_max = 2 << (8 * length_encoding);
if (length_encoding < 2 || length_encoding > 8 ||
input_len - auth_data_len > length_max) {
return CCM_ERR_INVALID_LENGTH_ENCODING;
}
/* Compute first stream block */
nonce_counter[0] = length_encoding - 1;
block_size = cipher_get_block_size(cipher);
memcpy(&nonce_counter[1], nonce, min(nonce_len, (size_t) 15 - length_encoding));
len = cipher_encrypt_ctr(cipher, nonce_counter, block_size, zero_block,
block_size, stream_block);
if (len < 0) {
return len;
}
/* Decrypt message in counter mode */
plain_len = input_len - mac_length;
crypto_block_inc_ctr(nonce_counter, block_size - nonce_len);
len = cipher_encrypt_ctr(cipher, nonce_counter, nonce_len, input,
plain_len, plain);
if (len < 0) {
return len;
}
/* Create B0, encrypt it (X1) and use it as mac_iv */
if (ccm_create_mac_iv(cipher, auth_data_len, mac_length, length_encoding,
nonce, nonce_len, plain_len, mac_iv) < 0) {
return CCM_ERR_INVALID_DATA_LENGTH;
}
/* MAC calulation (T) with additional data and plaintext */
ccm_compute_adata_mac(cipher, auth_data, auth_data_len, mac_iv);
len = ccm_compute_cbc_mac(cipher, mac_iv, plain, plain_len, mac);
if (len < 0) {
return len;
}
/* mac = input[plain_len...plain_len+mac_length] ^ first stream block */
for (uint8_t i = 0; i < mac_length; ++i) {
mac_recv[i] = input[len + i] ^ stream_block[i];
}
if (!crypto_equals(mac_recv, mac, mac_length)) {
return CCM_ERR_INVALID_CBC_MAC;
}
return plain_len;
}
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