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/******************************************************************************
*
* Copyright 2008-2012 Broadcom Corporation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at:
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
******************************************************************************/
/******************************************************************************
*
* This file contains the implementation of the AES128 and AES CMAC algorithm.
*
******************************************************************************/
#include "crypto_toolbox/aes.h"
#include "crypto_toolbox/crypto_toolbox.h"
namespace bluetooth {
namespace crypto_toolbox {
namespace {
typedef struct {
uint8_t* text;
uint16_t len;
uint16_t round;
} tCMAC_CB;
thread_local tCMAC_CB cmac_cb;
/* Rb for AES-128 as block cipher, LSB as [0] */
Octet16 const_Rb{0x87, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
/** utility function to do an biteise exclusive-OR of two bit strings of the
* length of OCTET16_LEN. Result is stored in first argument.
*/
static void xor_128(Octet16* a, const Octet16& b) {
// CHECK(a);
uint8_t i, *aa = a->data();
const uint8_t* bb = b.data();
for (i = 0; i < OCTET16_LEN; i++) {
aa[i] = aa[i] ^ bb[i];
}
}
} // namespace
/* This function computes AES_128(key, message) */
Octet16 aes_128(const Octet16& key, const Octet16& message) {
Octet16 key_reversed;
Octet16 message_reversed;
Octet16 output;
std::reverse_copy(key.begin(), key.end(), key_reversed.begin());
std::reverse_copy(message.begin(), message.end(), message_reversed.begin());
aes_context ctx;
aes_set_key(key_reversed.data(), key_reversed.size(), &ctx);
aes_encrypt(message_reversed.data(), output.data(), &ctx);
std::reverse(output.begin(), output.end());
return output;
}
/** utility function to padding the given text to be a 128 bits data. The
* parameter dest is input and output parameter, it must point to a
* OCTET16_LEN memory space; where include length bytes valid data. */
static void padding(Octet16* dest, uint8_t length) {
uint8_t i, *p = dest->data();
/* original last block */
for (i = length; i < OCTET16_LEN; i++) p[OCTET16_LEN - i - 1] = (i == length) ? 0x80 : 0;
}
/** utility function to left shift one bit for a 128 bits value. */
static void leftshift_onebit(uint8_t* input, uint8_t* output) {
uint8_t i, overflow = 0, next_overflow = 0;
/* input[0] is LSB */
for (i = 0; i < OCTET16_LEN; i++) {
next_overflow = (input[i] & 0x80) ? 1 : 0;
output[i] = (input[i] << 1) | overflow;
overflow = next_overflow;
}
return;
}
/** This function is the calculation of block cipher using AES-128. */
static Octet16 cmac_aes_k_calculate(const Octet16& key) {
Octet16 output;
Octet16 x{0}; // zero initialized
uint8_t i = 1;
while (i <= cmac_cb.round) {
/* Mi' := Mi (+) X */
xor_128((Octet16*)&cmac_cb.text[(cmac_cb.round - i) * OCTET16_LEN], x);
output = aes_128(key, &cmac_cb.text[(cmac_cb.round - i) * OCTET16_LEN], OCTET16_LEN);
x = output;
i++;
}
return output;
}
/** This function proceeed to prepare the last block of message Mn depending on
* the size of the message.
*/
static void cmac_prepare_last_block(const Octet16& k1, const Octet16& k2) {
// uint8_t x[16] = {0};
bool flag;
/* last block is a complete block set flag to 1 */
flag = ((cmac_cb.len % OCTET16_LEN) == 0 && cmac_cb.len != 0) ? true : false;
if (flag) { /* last block is complete block */
xor_128((Octet16*)&cmac_cb.text[0], k1);
} else /* padding then xor with k2 */
{
padding((Octet16*)&cmac_cb.text[0], (uint8_t)(cmac_cb.len % 16));
xor_128((Octet16*)&cmac_cb.text[0], k2);
}
}
/** This is the function to generate the two subkeys.
* |key| is CMAC key, expect SRK when used by SMP.
*/
static void cmac_generate_subkey(const Octet16& key) {
Octet16 zero{};
Octet16 p = aes_128(key, zero.data(), OCTET16_LEN);
Octet16 k1, k2;
uint8_t* pp = p.data();
/* If MSB(L) = 0, then K1 = L << 1 */
if ((pp[OCTET16_LEN - 1] & 0x80) != 0) {
/* Else K1 = ( L << 1 ) (+) Rb */
leftshift_onebit(pp, k1.data());
xor_128(&k1, const_Rb);
} else {
leftshift_onebit(pp, k1.data());
}
if ((k1[OCTET16_LEN - 1] & 0x80) != 0) {
/* K2 = (K1 << 1) (+) Rb */
leftshift_onebit(k1.data(), k2.data());
xor_128(&k2, const_Rb);
} else {
/* If MSB(K1) = 0, then K2 = K1 << 1 */
leftshift_onebit(k1.data(), k2.data());
}
cmac_prepare_last_block(k1, k2);
}
/** key - CMAC key in little endian order
* input - text to be signed in little endian byte order.
* length - length of the input in byte.
*/
Octet16 aes_cmac(const Octet16& key, const uint8_t* input, uint16_t length) {
uint16_t len, diff;
/* n is number of rounds */
uint16_t n = (length + OCTET16_LEN - 1) / OCTET16_LEN;
if (n == 0) n = 1;
len = n * OCTET16_LEN;
/* allocate a memory space of multiple of 16 bytes to hold text */
cmac_cb.text = (uint8_t*)alloca(len);
cmac_cb.round = n;
diff = len - length;
if (input != NULL && length > 0) {
memcpy(&cmac_cb.text[diff], input, (int)length);
cmac_cb.len = length;
} else {
cmac_cb.len = 0;
}
/* prepare calculation for subkey s and last block of data */
cmac_generate_subkey(key);
/* start calculation */
Octet16 signature = cmac_aes_k_calculate(key);
/* clean up */
memset(&cmac_cb, 0, sizeof(tCMAC_CB));
// cmac_cb.text is auto-freed by alloca
return signature;
}
} // namespace crypto_toolbox
} // namespace bluetooth