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@gmail.com, http://libtomcrypt.com
10 */
11 #include "tomcrypt.h"
12
13 /**
14 @file lrw_start.c
15 LRW_MODE implementation, start mode, Tom St Denis
16 */
17
18 #ifdef LTC_LRW_MODE
19
20 /**
21 Initialize the LRW context
22 @param cipher The cipher desired, must be a 128-bit block cipher
23 @param IV The index value, must be 128-bits
24 @param key The cipher key
25 @param keylen The length of the cipher key in octets
26 @param tweak The tweak value (second key), must be 128-bits
27 @param num_rounds The number of rounds for the cipher (0 == default)
28 @param lrw [out] The LRW state
29 @return CRYPT_OK on success.
30 */
lrw_start(int cipher,const unsigned char * IV,const unsigned char * key,int keylen,const unsigned char * tweak,int num_rounds,symmetric_LRW * lrw)31 int lrw_start( int cipher,
32 const unsigned char *IV,
33 const unsigned char *key, int keylen,
34 const unsigned char *tweak,
35 int num_rounds,
36 symmetric_LRW *lrw)
37 {
38 int err;
39 #ifdef LRW_TABLES
40 unsigned char B[16];
41 int x, y, z, t;
42 #endif
43
44 LTC_ARGCHK(IV != NULL);
45 LTC_ARGCHK(key != NULL);
46 LTC_ARGCHK(tweak != NULL);
47 LTC_ARGCHK(lrw != NULL);
48
49 #ifdef LTC_FAST
50 if (16 % sizeof(LTC_FAST_TYPE)) {
51 return CRYPT_INVALID_ARG;
52 }
53 #endif
54
55 /* is cipher valid? */
56 if ((err = cipher_is_valid(cipher)) != CRYPT_OK) {
57 return err;
58 }
59 if (cipher_descriptor[cipher].block_length != 16) {
60 return CRYPT_INVALID_CIPHER;
61 }
62
63 /* schedule key */
64 if ((err = cipher_descriptor[cipher].setup(key, keylen, num_rounds, &lrw->key)) != CRYPT_OK) {
65 return err;
66 }
67 lrw->cipher = cipher;
68
69 /* copy the IV and tweak */
70 XMEMCPY(lrw->tweak, tweak, 16);
71
72 #ifdef LRW_TABLES
73 /* setup tables */
74 /* generate the first table as it has no shifting (from which we make the other tables) */
75 zeromem(B, 16);
76 for (y = 0; y < 256; y++) {
77 B[0] = y;
78 gcm_gf_mult(tweak, B, &lrw->PC[0][y][0]);
79 }
80
81 /* now generate the rest of the tables based the previous table */
82 for (x = 1; x < 16; x++) {
83 for (y = 0; y < 256; y++) {
84 /* now shift it right by 8 bits */
85 t = lrw->PC[x-1][y][15];
86 for (z = 15; z > 0; z--) {
87 lrw->PC[x][y][z] = lrw->PC[x-1][y][z-1];
88 }
89 lrw->PC[x][y][0] = gcm_shift_table[t<<1];
90 lrw->PC[x][y][1] ^= gcm_shift_table[(t<<1)+1];
91 }
92 }
93 #endif
94
95 /* generate first pad */
96 return lrw_setiv(IV, 16, lrw);
97 }
98
99
100 #endif
101 /* $Source: /cvs/libtom/libtomcrypt/src/modes/lrw/lrw_start.c,v $ */
102 /* $Revision: 1.11 $ */
103 /* $Date: 2006/06/29 01:53:13 $ */
104