/* 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 $ */