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@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 */
cfb_decrypt(const unsigned char * ct,unsigned char * pt,unsigned long len,symmetric_CFB * cfb)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