| /* 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 |
| */ |
| |
| /** |
| @file gcm_init.c |
| GCM implementation, initialize state, by Tom St Denis |
| */ |
| #include "tomcrypt.h" |
| |
| #ifdef GCM_MODE |
| |
| /** |
| Initialize a GCM state |
| @param gcm The GCM state to initialize |
| @param cipher The index of the cipher to use |
| @param key The secret key |
| @param keylen The length of the secret key |
| @return CRYPT_OK on success |
| */ |
| int gcm_init(gcm_state *gcm, int cipher, |
| const unsigned char *key, int keylen) |
| { |
| int err; |
| unsigned char B[16]; |
| #ifdef GCM_TABLES |
| int x, y, z, t; |
| #endif |
| |
| LTC_ARGCHK(gcm != NULL); |
| LTC_ARGCHK(key != 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, 0, &gcm->K)) != CRYPT_OK) { |
| return err; |
| } |
| |
| /* H = E(0) */ |
| zeromem(B, 16); |
| if ((err = cipher_descriptor[cipher].ecb_encrypt(B, gcm->H, &gcm->K)) != CRYPT_OK) { |
| return err; |
| } |
| |
| /* setup state */ |
| zeromem(gcm->buf, sizeof(gcm->buf)); |
| zeromem(gcm->X, sizeof(gcm->X)); |
| gcm->cipher = cipher; |
| gcm->mode = GCM_MODE_IV; |
| gcm->ivmode = 0; |
| gcm->buflen = 0; |
| gcm->totlen = 0; |
| gcm->pttotlen = 0; |
| |
| #ifdef GCM_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(gcm->H, B, &gcm->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 = gcm->PC[x-1][y][15]; |
| for (z = 15; z > 0; z--) { |
| gcm->PC[x][y][z] = gcm->PC[x-1][y][z-1]; |
| } |
| gcm->PC[x][y][0] = gcm_shift_table[t<<1]; |
| gcm->PC[x][y][1] ^= gcm_shift_table[(t<<1)+1]; |
| } |
| } |
| |
| #endif |
| |
| return CRYPT_OK; |
| } |
| |
| #endif |
| |
| /* $Source: /cvs/libtom/libtomcrypt/src/encauth/gcm/gcm_init.c,v $ */ |
| /* $Revision: 1.18 $ */ |
| /* $Date: 2006/03/31 14:15:35 $ */ |