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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://libtom.org
*/
/**
@file ocb_init.c
OCB implementation, initialize state, by Tom St Denis
*/
#include "tomcrypt.h"
#ifdef LTC_OCB_MODE
static const struct {
int len;
unsigned char poly_div[MAXBLOCKSIZE],
poly_mul[MAXBLOCKSIZE];
} polys[] = {
{
8,
{ 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x0D },
{ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x1B }
}, {
16,
{ 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x43 },
{ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x87 }
}
};
/**
Initialize an OCB context.
@param ocb [out] The destination of the OCB state
@param cipher The index of the desired cipher
@param key The secret key
@param keylen The length of the secret key (octets)
@param nonce The session nonce (length of the block size of the cipher)
@return CRYPT_OK if successful
*/
int ocb_init(ocb_state *ocb, int cipher,
const unsigned char *key, unsigned long keylen, const unsigned char *nonce)
{
int poly, x, y, m, err;
LTC_ARGCHK(ocb != NULL);
LTC_ARGCHK(key != NULL);
LTC_ARGCHK(nonce != NULL);
/* valid cipher? */
if ((err = cipher_is_valid(cipher)) != CRYPT_OK) {
return err;
}
/* determine which polys to use */
ocb->block_len = cipher_descriptor[cipher].block_length;
for (poly = 0; poly < (int)(sizeof(polys)/sizeof(polys[0])); poly++) {
if (polys[poly].len == ocb->block_len) {
break;
}
}
if (polys[poly].len != ocb->block_len) {
return CRYPT_INVALID_ARG;
}
/* schedule the key */
if ((err = cipher_descriptor[cipher].setup(key, keylen, 0, &ocb->key)) != CRYPT_OK) {
return err;
}
/* find L = E[0] */
zeromem(ocb->L, ocb->block_len);
if ((err = cipher_descriptor[cipher].ecb_encrypt(ocb->L, ocb->L, &ocb->key)) != CRYPT_OK) {
return err;
}
/* find R = E[N xor L] */
for (x = 0; x < ocb->block_len; x++) {
ocb->R[x] = ocb->L[x] ^ nonce[x];
}
if ((err = cipher_descriptor[cipher].ecb_encrypt(ocb->R, ocb->R, &ocb->key)) != CRYPT_OK) {
return err;
}
/* find Ls[i] = L << i for i == 0..31 */
XMEMCPY(ocb->Ls[0], ocb->L, ocb->block_len);
for (x = 1; x < 32; x++) {
m = ocb->Ls[x-1][0] >> 7;
for (y = 0; y < ocb->block_len-1; y++) {
ocb->Ls[x][y] = ((ocb->Ls[x-1][y] << 1) | (ocb->Ls[x-1][y+1] >> 7)) & 255;
}
ocb->Ls[x][ocb->block_len-1] = (ocb->Ls[x-1][ocb->block_len-1] << 1) & 255;
if (m == 1) {
for (y = 0; y < ocb->block_len; y++) {
ocb->Ls[x][y] ^= polys[poly].poly_mul[y];
}
}
}
/* find Lr = L / x */
m = ocb->L[ocb->block_len-1] & 1;
/* shift right */
for (x = ocb->block_len - 1; x > 0; x--) {
ocb->Lr[x] = ((ocb->L[x] >> 1) | (ocb->L[x-1] << 7)) & 255;
}
ocb->Lr[0] = ocb->L[0] >> 1;
if (m == 1) {
for (x = 0; x < ocb->block_len; x++) {
ocb->Lr[x] ^= polys[poly].poly_div[x];
}
}
/* set Li, checksum */
zeromem(ocb->Li, ocb->block_len);
zeromem(ocb->checksum, ocb->block_len);
/* set other params */
ocb->block_index = 1;
ocb->cipher = cipher;
return CRYPT_OK;
}
#endif
/* $Source$ */
/* $Revision$ */
/* $Date$ */
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