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102 lines
2.8 KiB
C
102 lines
2.8 KiB
C
/* LibTomCrypt, modular cryptographic library -- Tom St Denis
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*
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* LibTomCrypt is a library that provides various cryptographic
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* algorithms in a highly modular and flexible manner.
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*
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* The library is free for all purposes without any express
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* guarantee it works.
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*/
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#include "tomcrypt.h"
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/**
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@file lrw_start.c
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LRW_MODE implementation, start mode, Tom St Denis
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*/
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#ifdef LTC_LRW_MODE
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/**
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Initialize the LRW context
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@param cipher The cipher desired, must be a 128-bit block cipher
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@param IV The index value, must be 128-bits
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@param key The cipher key
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@param keylen The length of the cipher key in octets
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@param tweak The tweak value (second key), must be 128-bits
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@param num_rounds The number of rounds for the cipher (0 == default)
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@param lrw [out] The LRW state
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@return CRYPT_OK on success.
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*/
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int lrw_start( int cipher,
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const unsigned char *IV,
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const unsigned char *key, int keylen,
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const unsigned char *tweak,
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int num_rounds,
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symmetric_LRW *lrw)
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{
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int err;
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#ifdef LTC_LRW_TABLES
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unsigned char B[16];
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int x, y, z, t;
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#endif
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LTC_ARGCHK(IV != NULL);
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LTC_ARGCHK(key != NULL);
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LTC_ARGCHK(tweak != NULL);
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LTC_ARGCHK(lrw != NULL);
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#ifdef LTC_FAST
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if (16 % sizeof(LTC_FAST_TYPE)) {
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return CRYPT_INVALID_ARG;
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}
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#endif
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/* is cipher valid? */
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if ((err = cipher_is_valid(cipher)) != CRYPT_OK) {
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return err;
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}
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if (cipher_descriptor[cipher].block_length != 16) {
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return CRYPT_INVALID_CIPHER;
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}
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/* schedule key */
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if ((err = cipher_descriptor[cipher].setup(key, keylen, num_rounds, &lrw->key)) != CRYPT_OK) {
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return err;
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}
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lrw->cipher = cipher;
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/* copy the IV and tweak */
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XMEMCPY(lrw->tweak, tweak, 16);
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#ifdef LTC_LRW_TABLES
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/* setup tables */
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/* generate the first table as it has no shifting (from which we make the other tables) */
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zeromem(B, 16);
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for (y = 0; y < 256; y++) {
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B[0] = y;
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gcm_gf_mult(tweak, B, &lrw->PC[0][y][0]);
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}
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/* now generate the rest of the tables based the previous table */
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for (x = 1; x < 16; x++) {
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for (y = 0; y < 256; y++) {
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/* now shift it right by 8 bits */
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t = lrw->PC[x-1][y][15];
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for (z = 15; z > 0; z--) {
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lrw->PC[x][y][z] = lrw->PC[x-1][y][z-1];
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}
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lrw->PC[x][y][0] = gcm_shift_table[t<<1];
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lrw->PC[x][y][1] ^= gcm_shift_table[(t<<1)+1];
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}
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}
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#endif
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/* generate first pad */
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return lrw_setiv(IV, 16, lrw);
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}
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#endif
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/* ref: HEAD -> master, tag: v1.18.2 */
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/* git commit: 7e7eb695d581782f04b24dc444cbfde86af59853 */
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/* commit time: 2018-07-01 22:49:01 +0200 */
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