64 lines
1.4 KiB
C
64 lines
1.4 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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/* OCB Implementation by Tom St Denis */
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#include "mycrypt.h"
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#ifdef OCB_MODE
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int ocb_decrypt(ocb_state *ocb, const unsigned char *ct, unsigned char *pt)
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{
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unsigned char Z[MAXBLOCKSIZE], tmp[MAXBLOCKSIZE];
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int err, x;
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_ARGCHK(ocb != NULL);
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_ARGCHK(pt != NULL);
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_ARGCHK(ct != NULL);
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/* check if valid cipher */
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if ((err = cipher_is_valid(ocb->cipher)) != CRYPT_OK) {
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return err;
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}
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_ARGCHK(cipher_descriptor[ocb->cipher].ecb_decrypt != NULL);
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/* check length */
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if (ocb->block_len != cipher_descriptor[ocb->cipher].block_length) {
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return CRYPT_INVALID_ARG;
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}
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/* Get Z[i] value */
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ocb_shift_xor(ocb, Z);
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/* xor ct in, encrypt, xor Z out */
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for (x = 0; x < ocb->block_len; x++) {
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tmp[x] = ct[x] ^ Z[x];
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}
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cipher_descriptor[ocb->cipher].ecb_decrypt(tmp, pt, &ocb->key);
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for (x = 0; x < ocb->block_len; x++) {
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pt[x] ^= Z[x];
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}
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/* compute checksum */
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for (x = 0; x < ocb->block_len; x++) {
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ocb->checksum[x] ^= pt[x];
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}
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#ifdef CLEAN_STACK
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zeromem(Z, sizeof(Z));
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zeromem(tmp, sizeof(tmp));
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#endif
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return CRYPT_OK;
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}
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#endif
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