77 lines
2.1 KiB
C
77 lines
2.1 KiB
C
/* LibTomCrypt, modular cryptographic library -- Tom St Denis
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*
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* LibTomCrypt is a library that provides various cryptographic
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* algorithms in a highly modular and flexible manner.
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*
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* The library is free for all purposes without any express
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* guarantee it works.
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*
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* Tom St Denis, tomstdenis@iahu.ca, http://libtomcrypt.org
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*/
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/* OMAC1 Support by Tom St Denis (for 64 and 128 bit block ciphers only) */
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#include "mycrypt.h"
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#ifdef OMAC
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int omac_init(omac_state *omac, int cipher, const unsigned char *key, unsigned long keylen)
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{
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int err, x, y, mask, msb, len;
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_ARGCHK(omac != NULL);
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_ARGCHK(key != NULL);
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/* schedule the key */
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if ((err = cipher_is_valid(cipher)) != CRYPT_OK) {
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return err;
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}
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/* now setup the system */
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switch (cipher_descriptor[cipher].block_length) {
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case 8: mask = 0x1B;
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len = 8;
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break;
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case 16: mask = 0x87;
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len = 16;
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break;
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default: return CRYPT_INVALID_ARG;
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}
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if ((err = cipher_descriptor[cipher].setup(key, keylen, 0, &omac->key)) != CRYPT_OK) {
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return err;
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}
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/* ok now we need Lu and Lu^2 [calc one from the other] */
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/* first calc L which is Ek(0) */
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zeromem(omac->Lu[0], cipher_descriptor[cipher].block_length);
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cipher_descriptor[cipher].ecb_encrypt(omac->Lu[0], omac->Lu[0], &omac->key);
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/* now do the mults, whoopy! */
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for (x = 0; x < 2; x++) {
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/* if msb(L * u^(x+1)) = 0 then just shift, otherwise shift and xor constant mask */
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msb = omac->Lu[x][0] >> 7;
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/* shift left */
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for (y = 0; y < (len - 1); y++) {
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omac->Lu[x][y] = ((omac->Lu[x][y] << 1) | (omac->Lu[x][y+1] >> 7)) & 255;
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}
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omac->Lu[x][len - 1] = ((omac->Lu[x][len - 1] << 1) ^ (msb ? mask : 0)) & 255;
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/* copy up as require */
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if (x == 0) {
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XMEMCPY(omac->Lu[1], omac->Lu[0], sizeof(omac->Lu[0]));
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}
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}
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/* setup state */
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omac->cipher_idx = cipher;
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omac->buflen = 0;
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omac->blklen = len;
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zeromem(omac->prev, sizeof(omac->prev));
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zeromem(omac->block, sizeof(omac->block));
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return CRYPT_OK;
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}
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#endif
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