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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
*/
/**
@file gcm_init.c
GCM implementation, initialize state, by Tom St Denis
*/
#include "tomcrypt.h"
#ifdef GCM_MODE
/**
Initialize a GCM state
@param gcm The GCM state to initialize
@param cipher The index of the cipher to use
@param key The secret key
@param keylen The length of the secret key
@return CRYPT_OK on success
*/
int gcm_init(gcm_state *gcm, int cipher,
const unsigned char *key, int keylen)
{
int err;
unsigned char B[16];
#ifdef GCM_TABLES
int x, y, z, t;
#endif
LTC_ARGCHK(gcm != NULL);
LTC_ARGCHK(key != 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, 0, &gcm->K)) != CRYPT_OK) {
return err;
}
/* H = E(0) */
zeromem(B, 16);
if ((err = cipher_descriptor[cipher].ecb_encrypt(B, gcm->H, &gcm->K)) != CRYPT_OK) {
return err;
}
/* setup state */
zeromem(gcm->buf, sizeof(gcm->buf));
zeromem(gcm->X, sizeof(gcm->X));
gcm->cipher = cipher;
gcm->mode = GCM_MODE_IV;
gcm->ivmode = 0;
gcm->buflen = 0;
gcm->totlen = 0;
gcm->pttotlen = 0;
#ifdef GCM_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(gcm->H, B, &gcm->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 = gcm->PC[x-1][y][15];
for (z = 15; z > 0; z--) {
gcm->PC[x][y][z] = gcm->PC[x-1][y][z-1];
}
gcm->PC[x][y][0] = gcm_shift_table[t<<1];
gcm->PC[x][y][1] ^= gcm_shift_table[(t<<1)+1];
}
}
#endif
return CRYPT_OK;
}
#endif
/* $Source: /cvs/libtom/libtomcrypt/src/encauth/gcm/gcm_init.c,v $ */
/* $Revision: 1.18 $ */
/* $Date: 2006/03/31 14:15:35 $ */
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