/* 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. * * Tom St Denis, tomstdenis@iahu.ca, http://libtomcrypt.org *//* OMAC1 Support by Tom St Denis (for 64 and 128 bit block ciphers only) */#include "mycrypt.h"#ifdef OMACint omac_init(omac_state *omac, int cipher, const unsigned char *key, unsigned long keylen){   int err, x, y, mask, msb, len;   _ARGCHK(omac != NULL);   _ARGCHK(key  != NULL);   /* schedule the key */   if ((err = cipher_is_valid(cipher)) != CRYPT_OK) {      return err;   }   /* now setup the system */   switch (cipher_descriptor[cipher].block_length) {       case 8:  mask = 0x1B;                len  = 8;                break;       case 16: mask = 0x87;                len  = 16;                break;       default: return CRYPT_INVALID_ARG;   }   if ((err = cipher_descriptor[cipher].setup(key, keylen, 0, &omac->key)) != CRYPT_OK) {      return err;   }   /* ok now we need Lu and Lu^2 [calc one from the other] */   /* first calc L which is Ek(0) */   zeromem(omac->Lu[0], cipher_descriptor[cipher].block_length);   cipher_descriptor[cipher].ecb_encrypt(omac->Lu[0], omac->Lu[0], &omac->key);   /* now do the mults, whoopy! */   for (x = 0; x < 2; x++) {       /* if msb(L * u^(x+1)) = 0 then just shift, otherwise shift and xor constant mask */       msb = omac->Lu[x][0] >> 7;       /* shift left */       for (y = 0; y < (len - 1); y++) {           omac->Lu[x][y] = ((omac->Lu[x][y] << 1) | (omac->Lu[x][y+1] >> 7)) & 255;       }       omac->Lu[x][len - 1] = ((omac->Lu[x][len - 1] << 1) ^ (msb ? mask : 0)) & 255;        /* copy up as require */       if (x == 0) {          memcpy(omac->Lu[1], omac->Lu[0], sizeof(omac->Lu[0]));       }   }   /* setup state */   omac->cipher_idx = cipher;   omac->buflen     = 0;   omac->blklen     = len;   zeromem(omac->prev,  sizeof(omac->prev));   zeromem(omac->block, sizeof(omac->block));   return CRYPT_OK;}#endif