/* 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@iahu.ca, http://libtomcrypt.org *//* OCB Implementation by Tom St Denis */#include "mycrypt.h"#ifdef OCB_MODEstatic 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 }}};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;   _ARGCHK(ocb   != NULL);   _ARGCHK(key   != NULL);   _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);   cipher_descriptor[cipher].ecb_encrypt(ocb->L, ocb->L, &ocb->key);   /* find R = E[N xor L] */   for (x = 0; x < ocb->block_len; x++) {       ocb->R[x] = ocb->L[x] ^ nonce[x];   }   cipher_descriptor[cipher].ecb_encrypt(ocb->R, ocb->R, &ocb->key);   /* find Ls[i] = L << i for i == 0..31 */   memcpy(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