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/* LibTomCrypt, modular cryptographic library -- Tom St Denis
*
* LibTomCrypt is a library that provides various cryptographic
* algorithms in a highly modular and flexible manner.
*
* The library is free for all purposes without any express
* guarantee it works.
*
* Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.org
*/
#include "tomcrypt.h"
/**
@file omac_init.c
OMAC1 support, initialize state, by Tom St Denis
*/
#ifdef OMAC
/**
Initialize an OMAC state
@param omac The OMAC state to initialize
@param cipher The index of the desired cipher
@param key The secret key
@param keylen The length of the secret key (octets)
@return CRYPT_OK if successful
*/
int omac_init(omac_state *omac, int cipher, const unsigned char *key, unsigned long keylen)
{
int err, x, y, mask, msb, len;
LTC_ARGCHK(omac != NULL);
LTC_ARGCHK(key != NULL);
/* schedule the key */
if ((err = cipher_is_valid(cipher)) != CRYPT_OK) {
return err;
}
#ifdef LTC_FAST
if (cipher_descriptor[cipher].block_length % sizeof(LTC_FAST_TYPE)) {
return CRYPT_INVALID_ARG;
}
#endif
/* now setup the system */
switch (cipher_descriptor[cipher].block_length) {
case 8: mask = 0x1B;
len = 8;
break;
case 16: mask = 0x87;
len = 16;
break;
default: return CRYPT_INVALID_ARG;
}
if ((err = cipher_descriptor[cipher].setup(key, keylen, 0, &omac->key)) != CRYPT_OK) {
return err;
}
/* ok now we need Lu and Lu^2 [calc one from the other] */
/* first calc L which is Ek(0) */
zeromem(omac->Lu[0], cipher_descriptor[cipher].block_length);
cipher_descriptor[cipher].ecb_encrypt(omac->Lu[0], omac->Lu[0], &omac->key);
/* now do the mults, whoopy! */
for (x = 0; x < 2; x++) {
/* if msb(L * u^(x+1)) = 0 then just shift, otherwise shift and xor constant mask */
msb = omac->Lu[x][0] >> 7;
/* shift left */
for (y = 0; y < (len - 1); y++) {
omac->Lu[x][y] = ((omac->Lu[x][y] << 1) | (omac->Lu[x][y+1] >> 7)) & 255;
}
omac->Lu[x][len - 1] = ((omac->Lu[x][len - 1] << 1) ^ (msb ? mask : 0)) & 255;
/* copy up as require */
if (x == 0) {
XMEMCPY(omac->Lu[1], omac->Lu[0], sizeof(omac->Lu[0]));
}
}
/* setup state */
omac->cipher_idx = cipher;
omac->buflen = 0;
omac->blklen = len;
zeromem(omac->prev, sizeof(omac->prev));
zeromem(omac->block, sizeof(omac->block));
return CRYPT_OK;
}
#endif
/* $Source: /cvs/libtom/libtomcrypt/src/mac/omac/omac_init.c,v $ */
/* $Revision: 1.5 $ */
/* $Date: 2005/06/06 10:22:44 $ */
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