1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis 2 * 3 * LibTomCrypt is a library that provides various cryptographic 4 * algorithms in a highly modular and flexible manner. 5 * 6 * The library is free for all purposes without any express 7 * guarantee it works. 8 * 9 * Tom St Denis, tomstdenis (at) gmail.com, http://libtomcrypt.com 10 */ 11 #include "tomcrypt.h" 12 13 /** 14 @file cfb_decrypt.c 15 CFB implementation, decrypt data, Tom St Denis 16 */ 17 18 #ifdef LTC_CFB_MODE 19 20 /** 21 CFB decrypt 22 @param ct Ciphertext 23 @param pt [out] Plaintext 24 @param len Length of ciphertext (octets) 25 @param cfb CFB state 26 @return CRYPT_OK if successful 27 */ 28 int cfb_decrypt(const unsigned char *ct, unsigned char *pt, unsigned long len, symmetric_CFB *cfb) 29 { 30 int err; 31 32 LTC_ARGCHK(pt != NULL); 33 LTC_ARGCHK(ct != NULL); 34 LTC_ARGCHK(cfb != NULL); 35 36 if ((err = cipher_is_valid(cfb->cipher)) != CRYPT_OK) { 37 return err; 38 } 39 40 /* is blocklen/padlen valid? */ 41 if (cfb->blocklen < 0 || cfb->blocklen > (int)sizeof(cfb->IV) || 42 cfb->padlen < 0 || cfb->padlen > (int)sizeof(cfb->pad)) { 43 return CRYPT_INVALID_ARG; 44 } 45 46 while (len-- > 0) { 47 if (cfb->padlen == cfb->blocklen) { 48 if ((err = cipher_descriptor[cfb->cipher].ecb_encrypt(cfb->pad, cfb->IV, &cfb->key)) != CRYPT_OK) { 49 return err; 50 } 51 cfb->padlen = 0; 52 } 53 cfb->pad[cfb->padlen] = *ct; 54 *pt = *ct ^ cfb->IV[cfb->padlen]; 55 ++pt; 56 ++ct; 57 ++(cfb->padlen); 58 } 59 return CRYPT_OK; 60 } 61 62 #endif 63 64 65 /* $Source: /cvs/libtom/libtomcrypt/src/modes/cfb/cfb_decrypt.c,v $ */ 66 /* $Revision: 1.7 $ */ 67 /* $Date: 2006/11/26 01:45:14 $ */ 68
