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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.com
*/
#include "tomcrypt.h"
/**
@file lrw_start.c
LRW_MODE implementation, start mode, Tom St Denis
*/
#ifdef LTC_LRW_MODE
/**
Initialize the LRW context
@param cipher The cipher desired, must be a 128-bit block cipher
@param IV The index value, must be 128-bits
@param key The cipher key
@param keylen The length of the cipher key in octets
@param tweak The tweak value (second key), must be 128-bits
@param num_rounds The number of rounds for the cipher (0 == default)
@param lrw [out] The LRW state
@return CRYPT_OK on success.
*/
int lrw_start( int cipher,
const unsigned char *IV,
const unsigned char *key, int keylen,
const unsigned char *tweak,
int num_rounds,
symmetric_LRW *lrw)
{
int err;
#ifdef LRW_TABLES
unsigned char B[16];
int x, y, z, t;
#endif
LTC_ARGCHK(IV != NULL);
LTC_ARGCHK(key != NULL);
LTC_ARGCHK(tweak != NULL);
LTC_ARGCHK(lrw != NULL);
#ifdef LTC_FAST
if (16 % sizeof(LTC_FAST_TYPE)) {
return CRYPT_INVALID_ARG;
}
#endif
/* is cipher valid? */
if ((err = cipher_is_valid(cipher)) != CRYPT_OK) {
return err;
}
if (cipher_descriptor[cipher].block_length != 16) {
return CRYPT_INVALID_CIPHER;
}
/* schedule key */
if ((err = cipher_descriptor[cipher].setup(key, keylen, num_rounds, &lrw->key)) != CRYPT_OK) {
return err;
}
lrw->cipher = cipher;
/* copy the IV and tweak */
XMEMCPY(lrw->tweak, tweak, 16);
#ifdef LRW_TABLES
/* setup tables */
/* generate the first table as it has no shifting (from which we make the other tables) */
zeromem(B, 16);
for (y = 0; y < 256; y++) {
B[0] = y;
gcm_gf_mult(tweak, B, &lrw->PC[0][y][0]);
}
/* now generate the rest of the tables based the previous table */
for (x = 1; x < 16; x++) {
for (y = 0; y < 256; y++) {
/* now shift it right by 8 bits */
t = lrw->PC[x-1][y][15];
for (z = 15; z > 0; z--) {
lrw->PC[x][y][z] = lrw->PC[x-1][y][z-1];
}
lrw->PC[x][y][0] = gcm_shift_table[t<<1];
lrw->PC[x][y][1] ^= gcm_shift_table[(t<<1)+1];
}
}
#endif
/* generate first pad */
return lrw_setiv(IV, 16, lrw);
}
#endif
/* $Source: /cvs/libtom/libtomcrypt/src/modes/lrw/lrw_start.c,v $ */
/* $Revision: 1.11 $ */
/* $Date: 2006/06/29 01:53:13 $ */
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