1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis */
2 /* SPDX-License-Identifier: Unlicense */
3 #include "tomcrypt_private.h"
4
5 /**
6 @file cfb_decrypt.c
7 CFB implementation, decrypt data, Tom St Denis
8 */
9
10 #ifdef LTC_CFB_MODE
11
12 /**
13 CFB decrypt
14 @param ct Ciphertext
15 @param pt [out] Plaintext
16 @param len Length of ciphertext (octets)
17 @param cfb CFB state
18 @return CRYPT_OK if successful
19 */
cfb_decrypt(const unsigned char * ct,unsigned char * pt,unsigned long len,symmetric_CFB * cfb)20 int cfb_decrypt(const unsigned char *ct, unsigned char *pt, unsigned long len, symmetric_CFB *cfb)
21 {
22 int err;
23
24 LTC_ARGCHK(pt != NULL);
25 LTC_ARGCHK(ct != NULL);
26 LTC_ARGCHK(cfb != NULL);
27
28 if ((err = cipher_is_valid(cfb->cipher)) != CRYPT_OK) {
29 return err;
30 }
31
32 /* is blocklen/padlen valid? */
33 if (cfb->blocklen < 0 || cfb->blocklen > (int)sizeof(cfb->IV) ||
34 cfb->padlen < 0 || cfb->padlen > (int)sizeof(cfb->pad)) {
35 return CRYPT_INVALID_ARG;
36 }
37
38 while (len-- > 0) {
39 if (cfb->padlen == cfb->blocklen) {
40 if ((err = cipher_descriptor[cfb->cipher]->ecb_encrypt(cfb->pad, cfb->IV, &cfb->key)) != CRYPT_OK) {
41 return err;
42 }
43 cfb->padlen = 0;
44 }
45 cfb->pad[cfb->padlen] = *ct;
46 *pt = *ct ^ cfb->IV[cfb->padlen];
47 ++pt;
48 ++ct;
49 ++(cfb->padlen);
50 }
51 return CRYPT_OK;
52 }
53
54 #endif
55
56