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 #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 */ 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
