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/* 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@gmail.com, http://libtom.org
*/
#include "tomcrypt.h"
/**
@file cfb_decrypt.c
CFB implementation, decrypt data, Tom St Denis
*/
#ifdef LTC_CFB_MODE
/**
CFB decrypt
@param ct Ciphertext
@param pt [out] Plaintext
@param len Length of ciphertext (octets)
@param cfb CFB state
@return CRYPT_OK if successful
*/
int cfb_decrypt(const unsigned char *ct, unsigned char *pt, unsigned long len, symmetric_CFB *cfb)
{
int err;
LTC_ARGCHK(pt != NULL);
LTC_ARGCHK(ct != NULL);
LTC_ARGCHK(cfb != NULL);
if ((err = cipher_is_valid(cfb->cipher)) != CRYPT_OK) {
return err;
}
/* is blocklen/padlen valid? */
if (cfb->blocklen < 0 || cfb->blocklen > (int)sizeof(cfb->IV) ||
cfb->padlen < 0 || cfb->padlen > (int)sizeof(cfb->pad)) {
return CRYPT_INVALID_ARG;
}
while (len-- > 0) {
if (cfb->padlen == cfb->blocklen) {
if ((err = cipher_descriptor[cfb->cipher].ecb_encrypt(cfb->pad, cfb->IV, &cfb->key)) != CRYPT_OK) {
return err;
}
cfb->padlen = 0;
}
cfb->pad[cfb->padlen] = *ct;
*pt = *ct ^ cfb->IV[cfb->padlen];
++pt;
++ct;
++(cfb->padlen);
}
return CRYPT_OK;
}
#endif
/* $Source$ */
/* $Revision$ */
/* $Date$ */
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