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 12 /** 13 @file gcm_init.c 14 GCM implementation, initialize state, by Tom St Denis 15 */ 16 #include "tomcrypt.h" 17 18 #ifdef GCM_MODE 19 20 /** 21 Initialize a GCM state 22 @param gcm The GCM state to initialize 23 @param cipher The index of the cipher to use 24 @param key The secret key 25 @param keylen The length of the secret key 26 @return CRYPT_OK on success 27 */ 28 int gcm_init(gcm_state *gcm, int cipher, 29 const unsigned char *key, int keylen) 30 { 31 int err; 32 unsigned char B[16]; 33 #ifdef GCM_TABLES 34 int x, y, z, t; 35 #endif 36 37 LTC_ARGCHK(gcm != NULL); 38 LTC_ARGCHK(key != NULL); 39 40 #ifdef LTC_FAST 41 if (16 % sizeof(LTC_FAST_TYPE)) { 42 return CRYPT_INVALID_ARG; 43 } 44 #endif 45 46 /* is cipher valid? */ 47 if ((err = cipher_is_valid(cipher)) != CRYPT_OK) { 48 return err; 49 } 50 if (cipher_descriptor[cipher].block_length != 16) { 51 return CRYPT_INVALID_CIPHER; 52 } 53 54 /* schedule key */ 55 if ((err = cipher_descriptor[cipher].setup(key, keylen, 0, &gcm->K)) != CRYPT_OK) { 56 return err; 57 } 58 59 /* H = E(0) */ 60 zeromem(B, 16); 61 if ((err = cipher_descriptor[cipher].ecb_encrypt(B, gcm->H, &gcm->K)) != CRYPT_OK) { 62 return err; 63 } 64 65 /* setup state */ 66 zeromem(gcm->buf, sizeof(gcm->buf)); 67 zeromem(gcm->X, sizeof(gcm->X)); 68 gcm->cipher = cipher; 69 gcm->mode = GCM_MODE_IV; 70 gcm->ivmode = 0; 71 gcm->buflen = 0; 72 gcm->totlen = 0; 73 gcm->pttotlen = 0; 74 75 #ifdef GCM_TABLES 76 /* setup tables */ 77 78 /* generate the first table as it has no shifting (from which we make the other tables) */ 79 zeromem(B, 16); 80 for (y = 0; y < 256; y++) { 81 B[0] = y; 82 gcm_gf_mult(gcm->H, B, &gcm->PC[0][y][0]); 83 } 84 85 /* now generate the rest of the tables based the previous table */ 86 for (x = 1; x < 16; x++) { 87 for (y = 0; y < 256; y++) { 88 /* now shift it right by 8 bits */ 89 t = gcm->PC[x-1][y][15]; 90 for (z = 15; z > 0; z--) { 91 gcm->PC[x][y][z] = gcm->PC[x-1][y][z-1]; 92 } 93 gcm->PC[x][y][0] = gcm_shift_table[t<<1]; 94 gcm->PC[x][y][1] ^= gcm_shift_table[(t<<1)+1]; 95 } 96 } 97 98 #endif 99 100 return CRYPT_OK; 101 } 102 103 #endif 104 105 /* $Source: /cvs/libtom/libtomcrypt/src/encauth/gcm/gcm_init.c,v $ */ 106 /* $Revision: 1.18 $ */ 107 /* $Date: 2006/03/31 14:15:35 $ */ 108
