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/* cmac.c - CMAC, Cipher-based MAC.
* Copyright © 2013 Jussi Kivilinna <jussi.kivilinna@iki.fi>
*
* This file is part of Libgcrypt.
*
* Libgcrypt is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* Libgcrypt is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this program; if not, see <http://www.gnu.org/licenses/>.
*/
#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "g10lib.h"
#include "cipher.h"
#include "cipher-internal.h"
#include "bufhelp.h"
#define set_burn(burn, nburn) do { \
unsigned int __nburn = (nburn); \
(burn) = (burn) > __nburn ? (burn) : __nburn; } while (0)
static void
cmac_write (gcry_cipher_hd_t c, const byte * inbuf, size_t inlen)
{
gcry_cipher_encrypt_t enc_fn = c->spec->encrypt;
const unsigned int blocksize = c->spec->blocksize;
byte outbuf[MAX_BLOCKSIZE];
unsigned int burn = 0;
unsigned int nblocks;
if (!inlen || !inbuf)
return;
/* Last block is needed for cmac_final. */
if (c->unused + inlen <= blocksize)
{
for (; inlen && c->unused < blocksize; inlen--)
c->lastiv[c->unused++] = *inbuf++;
return;
}
if (c->unused)
{
for (; inlen && c->unused < blocksize; inlen--)
c->lastiv[c->unused++] = *inbuf++;
buf_xor (c->u_iv.iv, c->u_iv.iv, c->lastiv, blocksize);
set_burn (burn, enc_fn (&c->context.c, c->u_iv.iv, c->u_iv.iv));
c->unused = 0;
}
if (c->bulk.cbc_enc && inlen > blocksize)
{
nblocks = inlen / blocksize;
nblocks -= (nblocks * blocksize == inlen);
c->bulk.cbc_enc (&c->context.c, c->u_iv.iv, outbuf, inbuf, nblocks, 1);
inbuf += nblocks * blocksize;
inlen -= nblocks * blocksize;
wipememory (outbuf, sizeof (outbuf));
}
else
while (inlen > blocksize)
{
buf_xor (c->u_iv.iv, c->u_iv.iv, inbuf, blocksize);
set_burn (burn, enc_fn (&c->context.c, c->u_iv.iv, c->u_iv.iv));
inlen -= blocksize;
inbuf += blocksize;
}
/* Make sure that last block is passed to cmac_final. */
if (inlen == 0)
BUG ();
for (; inlen && c->unused < blocksize; inlen--)
c->lastiv[c->unused++] = *inbuf++;
if (burn)
_gcry_burn_stack (burn + 4 * sizeof (void *));
}
static void
cmac_generate_subkeys (gcry_cipher_hd_t c)
{
const unsigned int blocksize = c->spec->blocksize;
byte rb, carry, t, bi;
unsigned int burn;
int i, j;
union
{
size_t _aligned;
byte buf[MAX_BLOCKSIZE];
} u;
if (MAX_BLOCKSIZE < blocksize)
BUG ();
/* encrypt zero block */
memset (u.buf, 0, blocksize);
burn = c->spec->encrypt (&c->context.c, u.buf, u.buf);
/* Currently supported blocksizes are 16 and 8. */
rb = blocksize == 16 ? 0x87 : 0x1B /*blocksize == 8 */ ;
for (j = 0; j < 2; j++)
{
/* Generate subkeys K1 and K2 */
carry = 0;
for (i = blocksize - 1; i >= 0; i--)
{
bi = u.buf[i];
t = carry | (bi << 1);
carry = bi >> 7;
u.buf[i] = t & 0xff;
c->u_mode.cmac.subkeys[j][i] = u.buf[i];
}
u.buf[blocksize - 1] ^= carry ? rb : 0;
c->u_mode.cmac.subkeys[j][blocksize - 1] = u.buf[blocksize - 1];
}
wipememory (&u, sizeof (u));
if (burn)
_gcry_burn_stack (burn + 4 * sizeof (void *));
}
static void
cmac_final (gcry_cipher_hd_t c)
{
const unsigned int blocksize = c->spec->blocksize;
unsigned int count = c->unused;
unsigned int burn;
byte *subkey;
if (count == blocksize)
subkey = c->u_mode.cmac.subkeys[0]; /* K1 */
else
{
subkey = c->u_mode.cmac.subkeys[1]; /* K2 */
c->lastiv[count++] = 0x80;
while (count < blocksize)
c->lastiv[count++] = 0;
}
buf_xor (c->lastiv, c->lastiv, subkey, blocksize);
buf_xor (c->u_iv.iv, c->u_iv.iv, c->lastiv, blocksize);
burn = c->spec->encrypt (&c->context.c, c->u_iv.iv, c->u_iv.iv);
if (burn)
_gcry_burn_stack (burn + 4 * sizeof (void *));
c->unused = 0;
}
static gcry_err_code_t
cmac_tag (gcry_cipher_hd_t c, unsigned char *tag, size_t taglen, int check)
{
if (!tag || taglen == 0 || taglen > c->spec->blocksize)
return GPG_ERR_INV_ARG;
if (!c->u_mode.cmac.tag)
{
cmac_final (c);
c->u_mode.cmac.tag = 1;
}
if (!check)
{
memcpy (tag, c->u_iv.iv, taglen);
return GPG_ERR_NO_ERROR;
}
else
{
return buf_eq_const (tag, c->u_iv.iv, taglen) ?
GPG_ERR_NO_ERROR : GPG_ERR_CHECKSUM;
}
}
gcry_err_code_t
_gcry_cipher_cmac_authenticate (gcry_cipher_hd_t c,
const unsigned char *abuf, size_t abuflen)
{
if (abuflen > 0 && !abuf)
return GPG_ERR_INV_ARG;
if (c->u_mode.cmac.tag)
return GPG_ERR_INV_STATE;
/* To support new blocksize, update cmac_generate_subkeys() then add new
blocksize here. */
if (c->spec->blocksize != 16 && c->spec->blocksize != 8)
return GPG_ERR_INV_CIPHER_MODE;
cmac_write (c, abuf, abuflen);
return GPG_ERR_NO_ERROR;
}
gcry_err_code_t
_gcry_cipher_cmac_get_tag (gcry_cipher_hd_t c,
unsigned char *outtag, size_t taglen)
{
return cmac_tag (c, outtag, taglen, 0);
}
gcry_err_code_t
_gcry_cipher_cmac_check_tag (gcry_cipher_hd_t c,
const unsigned char *intag, size_t taglen)
{
return cmac_tag (c, (unsigned char *) intag, taglen, 1);
}
gcry_err_code_t
_gcry_cipher_cmac_set_subkeys (gcry_cipher_hd_t c)
{
cmac_generate_subkeys (c);
return GPG_ERR_NO_ERROR;
}
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