| /* 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 $ */ |