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