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      1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis
      2  *
      3  * LibTomCrypt is a library that provides various cryptographic
      4  * algorithms in a highly modular and flexible manner.
      5  *
      6  * The library is free for all purposes without any express
      7  * guarantee it works.
      8  *
      9  * Tom St Denis, tomstdenis (at) gmail.com, http://libtomcrypt.com
     10  */
     11 #include "tomcrypt.h"
     12 
     13 /**
     14    @file lrw_start.c
     15    LRW_MODE implementation, start mode, Tom St Denis
     16 */
     17 
     18 #ifdef LTC_LRW_MODE
     19 
     20 /**
     21   Initialize the LRW context
     22   @param cipher        The cipher desired, must be a 128-bit block cipher
     23   @param IV            The index value, must be 128-bits
     24   @param key           The cipher key
     25   @param keylen        The length of the cipher key in octets
     26   @param tweak         The tweak value (second key), must be 128-bits
     27   @param num_rounds    The number of rounds for the cipher (0 == default)
     28   @param lrw           [out] The LRW state
     29   @return CRYPT_OK on success.
     30 */
     31 int lrw_start(               int   cipher,
     32               const unsigned char *IV,
     33               const unsigned char *key,       int keylen,
     34               const unsigned char *tweak,
     35                              int  num_rounds,
     36                    symmetric_LRW *lrw)
     37 {
     38    int           err;
     39 #ifdef LRW_TABLES
     40    unsigned char B[16];
     41    int           x, y, z, t;
     42 #endif
     43 
     44   LTC_ARGCHK(IV    != NULL);
     45   LTC_ARGCHK(key   != NULL);
     46   LTC_ARGCHK(tweak != NULL);
     47   LTC_ARGCHK(lrw   != NULL);
     48 
     49 #ifdef LTC_FAST
     50    if (16 % sizeof(LTC_FAST_TYPE)) {
     51       return CRYPT_INVALID_ARG;
     52    }
     53 #endif
     54 
     55    /* is cipher valid? */
     56    if ((err = cipher_is_valid(cipher)) != CRYPT_OK) {
     57       return err;
     58    }
     59    if (cipher_descriptor[cipher].block_length != 16) {
     60       return CRYPT_INVALID_CIPHER;
     61    }
     62 
     63    /* schedule key */
     64    if ((err = cipher_descriptor[cipher].setup(key, keylen, num_rounds, &lrw->key)) != CRYPT_OK) {
     65       return err;
     66    }
     67    lrw->cipher = cipher;
     68 
     69    /* copy the IV and tweak */
     70    XMEMCPY(lrw->tweak, tweak, 16);
     71 
     72 #ifdef LRW_TABLES
     73    /* setup tables */
     74    /* generate the first table as it has no shifting (from which we make the other tables) */
     75    zeromem(B, 16);
     76    for (y = 0; y < 256; y++) {
     77         B[0] = y;
     78         gcm_gf_mult(tweak, B, &lrw->PC[0][y][0]);
     79    }
     80 
     81    /* now generate the rest of the tables based the previous table */
     82    for (x = 1; x < 16; x++) {
     83       for (y = 0; y < 256; y++) {
     84          /* now shift it right by 8 bits */
     85          t = lrw->PC[x-1][y][15];
     86          for (z = 15; z > 0; z--) {
     87              lrw->PC[x][y][z] = lrw->PC[x-1][y][z-1];
     88          }
     89          lrw->PC[x][y][0]  = gcm_shift_table[t<<1];
     90          lrw->PC[x][y][1] ^= gcm_shift_table[(t<<1)+1];
     91      }
     92   }
     93 #endif
     94 
     95    /* generate first pad */
     96    return lrw_setiv(IV, 16, lrw);
     97 }
     98 
     99 
    100 #endif
    101 /* $Source: /cvs/libtom/libtomcrypt/src/modes/lrw/lrw_start.c,v $ */
    102 /* $Revision: 1.11 $ */
    103 /* $Date: 2006/06/29 01:53:13 $ */
    104