127 lines
3.0 KiB
C
127 lines
3.0 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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/* EAX Implementation by Tom St Denis */
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#include "mycrypt.h"
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#ifdef EAX_MODE
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int eax_init(eax_state *eax, int cipher, const unsigned char *key, unsigned long keylen,
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const unsigned char *nonce, unsigned long noncelen,
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const unsigned char *header, unsigned long headerlen)
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{
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unsigned char *buf;
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int err, blklen;
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omac_state *omac;
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unsigned long len;
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_ARGCHK(eax != NULL);
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_ARGCHK(key != NULL);
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_ARGCHK(nonce != NULL);
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if (headerlen > 0) {
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_ARGCHK(header != NULL);
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}
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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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blklen = cipher_descriptor[cipher].block_length;
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/* allocate ram */
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buf = XMALLOC(MAXBLOCKSIZE);
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omac = XMALLOC(sizeof(omac_state));
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if (buf == NULL || omac == NULL) {
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if (buf != NULL) {
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XFREE(buf);
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}
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if (omac != NULL) {
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XFREE(omac);
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}
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return CRYPT_MEM;
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}
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/* N = OMAC_0K(nonce) */
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zeromem(buf, MAXBLOCKSIZE);
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if ((err = omac_init(omac, cipher, key, keylen)) != CRYPT_OK) {
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goto __ERR;
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}
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/* omac the [0]_n */
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if ((err = omac_process(omac, buf, blklen)) != CRYPT_OK) {
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goto __ERR;
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}
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/* omac the nonce */
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if ((err = omac_process(omac, nonce, noncelen)) != CRYPT_OK) {
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goto __ERR;
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}
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/* store result */
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len = sizeof(eax->N);
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if ((err = omac_done(omac, eax->N, &len)) != CRYPT_OK) {
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goto __ERR;
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}
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/* H = OMAC_1K(header) */
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zeromem(buf, MAXBLOCKSIZE);
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buf[blklen - 1] = 1;
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if ((err = omac_init(&eax->headeromac, cipher, key, keylen)) != CRYPT_OK) {
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goto __ERR;
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}
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/* omac the [1]_n */
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if ((err = omac_process(&eax->headeromac, buf, blklen)) != CRYPT_OK) {
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goto __ERR;
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}
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/* omac the header */
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if (headerlen != 0) {
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if ((err = omac_process(&eax->headeromac, header, headerlen)) != CRYPT_OK) {
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goto __ERR;
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}
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}
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/* note we don't finish the headeromac, this allows us to add more header later */
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/* setup the CTR mode */
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if ((err = ctr_start(cipher, eax->N, key, keylen, 0, &eax->ctr)) != CRYPT_OK) {
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goto __ERR;
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}
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/* use big-endian counter */
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eax->ctr.mode = 1;
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/* setup the OMAC for the ciphertext */
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if ((err = omac_init(&eax->ctomac, cipher, key, keylen)) != CRYPT_OK) {
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goto __ERR;
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}
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/* omac [2]_n */
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zeromem(buf, MAXBLOCKSIZE);
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buf[blklen-1] = 2;
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if ((err = omac_process(&eax->ctomac, buf, blklen)) != CRYPT_OK) {
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goto __ERR;
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}
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err = CRYPT_OK;
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__ERR:
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#ifdef CLEAN_STACK
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zeromem(buf, MAXBLOCKSIZE);
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zeromem(omac, sizeof(omac_state));
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#endif
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XFREE(omac);
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XFREE(buf);
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return err;
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}
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#endif
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