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/*
* Copyright (C) 2016 Fundación Inria Chile
*
* 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_hashes_cmac
* @{
*
* @file
* @brief AES_CMAC implementation
*
* @author José Ignacio Alamos <jose.alamos@inria.cl>
*
* @}
*/
#include <inttypes.h>
#include <stdio.h>
#include <string.h>
#include "crypto/ciphers.h"
#include "hashes/cmac.h"
#define MIN(a, b) a < b ? a : b
static void _xor128(uint8_t *x, uint8_t *y)
{
for (unsigned i = 0; i < 16; i++) {
y[i] = x[i] ^ y[i];
}
}
static void _leftshift(uint8_t *x, uint8_t *y)
{
for (unsigned i = 0; i < 15; i++) {
y[i] = (x[i] << 1) | (x[i + 1] >> 7);
}
y[15] = x[15] << 1;
}
int cmac_init(cmac_context_t *ctx, const uint8_t *key, uint8_t key_size)
{
if (key_size != CMAC_BLOCK_SIZE) {
return CIPHER_ERR_INVALID_KEY_SIZE;
}
memset(ctx, 0, sizeof(cmac_context_t));
return cipher_init(&(ctx->aes_ctx), CIPHER_AES_128, key, key_size);
}
void cmac_update(cmac_context_t *ctx, const void *data, size_t len)
{
uint8_t d[16];
while (len) {
uint8_t c;
if (ctx->M_n == 16) {
ctx->M_n = 0;
_xor128(ctx->M_last, ctx->X);
cipher_encrypt(&ctx->aes_ctx, ctx->X, d);
memcpy(ctx->X, d, CMAC_BLOCK_SIZE);
}
c = MIN(CMAC_BLOCK_SIZE - ctx->M_n, len);
memcpy(ctx->M_last + ctx->M_n, data, c);
ctx->M_n += c;
len -= c;
data = (void *) (((uint8_t *) data) + c);
if (ctx->M_n < CMAC_BLOCK_SIZE) {
break;
}
}
}
void cmac_final(cmac_context_t *ctx, void *digest)
{
/* Generate subkeys */
uint8_t K[CMAC_BLOCK_SIZE];
uint8_t L[CMAC_BLOCK_SIZE];
memset(K, 0, CMAC_BLOCK_SIZE);
cipher_encrypt(&ctx->aes_ctx, K, L);
if (L[0] & 0x80) {
_leftshift(L, K);
K[15] ^= 0x87;
}
else {
_leftshift(L, K);
}
if (ctx->M_n != 16) {
/* Generate K2 */
if (K[0] & 0x80) {
_leftshift(K, K);
K[15] ^= 0x87;
}
else {
_leftshift(K, K);
}
/* Padding */
memset(ctx->M_last + ctx->M_n, 0, CMAC_BLOCK_SIZE - ctx->M_n);
ctx->M_last[ctx->M_n] = 0x80;
}
_xor128(K, ctx->M_last);
_xor128(ctx->M_last, ctx->X);
cipher_encrypt(&ctx->aes_ctx, ctx->X, L);
memcpy(digest, L, CMAC_BLOCK_SIZE);
}