MIK / CryptX-0.059_002 / src / ltc / encauth / gcm / gcm_init.c 

            

              
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105

              
/* 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.
 */
/**
   @file gcm_init.c
   GCM implementation, initialize state, by Tom St Denis
*/
#include "tomcrypt.h"
#ifdef LTC_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 LTC_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     = LTC_GCM_MODE_IV;
   gcm->ivmode   = 0;
   gcm->buflen   = 0;
   gcm->totlen   = 0;
   gcm->pttotlen = 0;
#ifdef LTC_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
/* ref:         $Format:%D$ */
/* git commit:  $Format:%H$ */
/* commit time: $Format:%ai$ */