1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis */
2 /* SPDX-License-Identifier: Unlicense */
3 #include "tomcrypt_private.h"
4
5 /**
6 @file lrw_start.c
7 LRW_MODE implementation, start mode, Tom St Denis
8 */
9
10 #ifdef LTC_LRW_MODE
11
12 /**
13 Initialize the LRW context
14 @param cipher The cipher desired, must be a 128-bit block cipher
15 @param IV The index value, must be 128-bits
16 @param key The cipher key
17 @param keylen The length of the cipher key in octets
18 @param tweak The tweak value (second key), must be 128-bits
19 @param num_rounds The number of rounds for the cipher (0 == default)
20 @param lrw [out] The LRW state
21 @return CRYPT_OK on success.
22 */
lrw_start(int cipher,const unsigned char * IV,const unsigned char * key,int keylen,const unsigned char * tweak,int num_rounds,symmetric_LRW * lrw)23 int lrw_start( int cipher,
24 const unsigned char *IV,
25 const unsigned char *key, int keylen,
26 const unsigned char *tweak,
27 int num_rounds,
28 symmetric_LRW *lrw)
29 {
30 int err;
31 #ifdef LTC_LRW_TABLES
32 unsigned char B[16];
33 int x, y, z, t;
34 #endif
35
36 LTC_ARGCHK(IV != NULL);
37 LTC_ARGCHK(key != NULL);
38 LTC_ARGCHK(tweak != NULL);
39 LTC_ARGCHK(lrw != NULL);
40
41 #ifdef LTC_FAST
42 if (16 % sizeof(LTC_FAST_TYPE)) {
43 return CRYPT_INVALID_ARG;
44 }
45 #endif
46
47 /* is cipher valid? */
48 if ((err = cipher_is_valid(cipher)) != CRYPT_OK) {
49 return err;
50 }
51 if (cipher_descriptor[cipher]->block_length != 16) {
52 return CRYPT_INVALID_CIPHER;
53 }
54
55 /* schedule key */
56 if ((err = cipher_descriptor[cipher]->setup(key, keylen, num_rounds, &lrw->key)) != CRYPT_OK) {
57 return err;
58 }
59 lrw->cipher = cipher;
60
61 /* copy the IV and tweak */
62 XMEMCPY(lrw->tweak, tweak, 16);
63
64 #ifdef LTC_LRW_TABLES
65 /* setup tables */
66 /* generate the first table as it has no shifting (from which we make the other tables) */
67 zeromem(B, 16);
68 for (y = 0; y < 256; y++) {
69 B[0] = y;
70 gcm_gf_mult(tweak, B, &lrw->PC[0][y][0]);
71 }
72
73 /* now generate the rest of the tables based the previous table */
74 for (x = 1; x < 16; x++) {
75 for (y = 0; y < 256; y++) {
76 /* now shift it right by 8 bits */
77 t = lrw->PC[x-1][y][15];
78 for (z = 15; z > 0; z--) {
79 lrw->PC[x][y][z] = lrw->PC[x-1][y][z-1];
80 }
81 lrw->PC[x][y][0] = gcm_shift_table[t<<1];
82 lrw->PC[x][y][1] ^= gcm_shift_table[(t<<1)+1];
83 }
84 }
85 #endif
86
87 /* generate first pad */
88 return lrw_setiv(IV, 16, lrw);
89 }
90
91
92 #endif
93