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 omac_init.c
15 OMAC1 support, initialize state, by Tom St Denis
16 */
17
18
19 #ifdef LTC_OMAC
20
21 /**
22 Initialize an OMAC state
23 @param omac The OMAC state to initialize
24 @param cipher The index of the desired cipher
25 @param key The secret key
26 @param keylen The length of the secret key (octets)
27 @return CRYPT_OK if successful
28 */
omac_init(omac_state * omac,int cipher,const unsigned char * key,unsigned long keylen)29 int omac_init(omac_state *omac, int cipher, const unsigned char *key, unsigned long keylen)
30 {
31 int err, x, y, mask, msb, len;
32
33 LTC_ARGCHK(omac != NULL);
34 LTC_ARGCHK(key != NULL);
35
36 /* schedule the key */
37 if ((err = cipher_is_valid(cipher)) != CRYPT_OK) {
38 return err;
39 }
40
41 #ifdef LTC_FAST
42 if (cipher_descriptor[cipher].block_length % sizeof(LTC_FAST_TYPE)) {
43 return CRYPT_INVALID_ARG;
44 }
45 #endif
46
47 /* now setup the system */
48 switch (cipher_descriptor[cipher].block_length) {
49 case 8: mask = 0x1B;
50 len = 8;
51 break;
52 case 16: mask = 0x87;
53 len = 16;
54 break;
55 default: return CRYPT_INVALID_ARG;
56 }
57
58 if ((err = cipher_descriptor[cipher].setup(key, keylen, 0, &omac->key)) != CRYPT_OK) {
59 return err;
60 }
61
62 /* ok now we need Lu and Lu^2 [calc one from the other] */
63
64 /* first calc L which is Ek(0) */
65 zeromem(omac->Lu[0], cipher_descriptor[cipher].block_length);
66 if ((err = cipher_descriptor[cipher].ecb_encrypt(omac->Lu[0], omac->Lu[0], &omac->key)) != CRYPT_OK) {
67 return err;
68 }
69
70 /* now do the mults, whoopy! */
71 for (x = 0; x < 2; x++) {
72 /* if msb(L * u^(x+1)) = 0 then just shift, otherwise shift and xor constant mask */
73 msb = omac->Lu[x][0] >> 7;
74
75 /* shift left */
76 for (y = 0; y < (len - 1); y++) {
77 omac->Lu[x][y] = ((omac->Lu[x][y] << 1) | (omac->Lu[x][y+1] >> 7)) & 255;
78 }
79 omac->Lu[x][len - 1] = ((omac->Lu[x][len - 1] << 1) ^ (msb ? mask : 0)) & 255;
80
81 /* copy up as require */
82 if (x == 0) {
83 XMEMCPY(omac->Lu[1], omac->Lu[0], sizeof(omac->Lu[0]));
84 }
85 }
86
87 /* setup state */
88 omac->cipher_idx = cipher;
89 omac->buflen = 0;
90 omac->blklen = len;
91 zeromem(omac->prev, sizeof(omac->prev));
92 zeromem(omac->block, sizeof(omac->block));
93
94 return CRYPT_OK;
95 }
96
97 #endif
98
99 /* $Source: /cvs/libtom/libtomcrypt/src/mac/omac/omac_init.c,v $ */
100 /* $Revision: 1.10 $ */
101 /* $Date: 2006/11/03 00:39:49 $ */
102