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106 lines
2.6 KiB
C
106 lines
2.6 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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/**
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@file gcm_init.c
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GCM implementation, initialize state, by Tom St Denis
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*/
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#include "tomcrypt.h"
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#ifdef LTC_GCM_MODE
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/**
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Initialize a GCM state
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@param gcm The GCM state to initialize
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@param cipher The index of the cipher to use
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@param key The secret key
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@param keylen The length of the secret key
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@return CRYPT_OK on success
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*/
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int gcm_init(gcm_state *gcm, int cipher,
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const unsigned char *key, int keylen)
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{
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int err;
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unsigned char B[16];
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#ifdef LTC_GCM_TABLES
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int x, y, z, t;
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#endif
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LTC_ARGCHK(gcm != NULL);
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LTC_ARGCHK(key != 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, 0, &gcm->K)) != CRYPT_OK) {
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return err;
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}
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/* H = E(0) */
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zeromem(B, 16);
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if ((err = cipher_descriptor[cipher].ecb_encrypt(B, gcm->H, &gcm->K)) != CRYPT_OK) {
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return err;
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}
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/* setup state */
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zeromem(gcm->buf, sizeof(gcm->buf));
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zeromem(gcm->X, sizeof(gcm->X));
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gcm->cipher = cipher;
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gcm->mode = LTC_GCM_MODE_IV;
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gcm->ivmode = 0;
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gcm->buflen = 0;
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gcm->totlen = 0;
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gcm->pttotlen = 0;
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#ifdef LTC_GCM_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(gcm->H, B, &gcm->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 = gcm->PC[x-1][y][15];
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for (z = 15; z > 0; z--) {
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gcm->PC[x][y][z] = gcm->PC[x-1][y][z-1];
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}
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gcm->PC[x][y][0] = gcm_shift_table[t<<1];
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gcm->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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return CRYPT_OK;
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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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