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/* $OpenBSD: cmac.c,v 1.1 2008/08/12 15:43:00 damien Exp $ */
/*-
* Copyright (c) 2008 Damien Bergamini <damien.bergamini@free.fr>
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
/*
* This code implements the CMAC (Cipher-based Message Authentication)
* algorithm described in FIPS SP800-38B using the AES-128 cipher.
*/
#include <sys/param.h>
#include <sys/systm.h>
#include <crypto/rijndael.h>
#include <crypto/cmac.h>
#define LSHIFT(v, r) do { \
int i; \
for (i = 0; i < 15; i++) \
(r)[i] = (v)[i] << 1 | (v)[i + 1] >> 7; \
(r)[15] = (v)[15] << 1; \
} while (0)
#define XOR(v, r) do { \
int i; \
for (i = 0; i < 16; i++) \
(r)[i] ^= (v)[i]; \
} while (0)
void
AES_CMAC_Init(AES_CMAC_CTX *ctx)
{
memset(ctx->X, 0, sizeof ctx->X);
ctx->M_n = 0;
}
void
AES_CMAC_SetKey(AES_CMAC_CTX *ctx, const u_int8_t key[AES_CMAC_KEY_LENGTH])
{
rijndael_set_key_enc_only(&ctx->rijndael, key, 128);
}
void
AES_CMAC_Update(AES_CMAC_CTX *ctx, const u_int8_t *data, u_int len)
{
u_int mlen;
if (ctx->M_n > 0) {
mlen = MIN(16 - ctx->M_n, len);
memcpy(ctx->M_last + ctx->M_n, data, mlen);
ctx->M_n += mlen;
if (ctx->M_n < 16 || len == mlen)
return;
XOR(ctx->M_last, ctx->X);
rijndael_encrypt(&ctx->rijndael, ctx->X, ctx->X);
data += mlen;
len -= mlen;
}
while (len > 16) { /* not last block */
XOR(data, ctx->X);
rijndael_encrypt(&ctx->rijndael, ctx->X, ctx->X);
data += 16;
len -= 16;
}
/* potential last block, save it */
memcpy(ctx->M_last, data, len);
ctx->M_n = len;
}
void
AES_CMAC_Final(u_int8_t digest[AES_CMAC_DIGEST_LENGTH], AES_CMAC_CTX *ctx)
{
u_int8_t K[16];
/* generate subkey K1 */
memset(K, 0, sizeof K);
rijndael_encrypt(&ctx->rijndael, K, K);
if (K[0] & 0x80) {
LSHIFT(K, K);
K[15] ^= 0x87;
} else
LSHIFT(K, K);
if (ctx->M_n == 16) {
/* last block was a complete block */
XOR(K, ctx->M_last);
} else {
/* generate subkey K2 */
if (K[0] & 0x80) {
LSHIFT(K, K);
K[15] ^= 0x87;
} else
LSHIFT(K, K);
/* padding(M_last) */
ctx->M_last[ctx->M_n] = 0x80;
while (++ctx->M_n < 16)
ctx->M_last[ctx->M_n] = 0;
XOR(K, ctx->M_last);
}
XOR(ctx->M_last, ctx->X);
rijndael_encrypt(&ctx->rijndael, ctx->X, digest);
memset(K, 0, sizeof K);
}
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