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 cbc_decrypt.c
15 CBC implementation, encrypt block, Tom St Denis
16 */
17
18
19 #ifdef LTC_CBC_MODE
20
21 /**
22 CBC decrypt
23 @param ct Ciphertext
24 @param pt [out] Plaintext
25 @param len The number of bytes to process (must be multiple of block length)
26 @param cbc CBC state
27 @return CRYPT_OK if successful
28 */
cbc_decrypt(const unsigned char * ct,unsigned char * pt,unsigned long len,symmetric_CBC * cbc)29 int cbc_decrypt(const unsigned char *ct, unsigned char *pt, unsigned long len, symmetric_CBC *cbc)
30 {
31 int x, err;
32 unsigned char tmp[16];
33 #ifdef LTC_FAST
34 LTC_FAST_TYPE tmpy;
35 #else
36 unsigned char tmpy;
37 #endif
38
39 LTC_ARGCHK(pt != NULL);
40 LTC_ARGCHK(ct != NULL);
41 LTC_ARGCHK(cbc != NULL);
42
43 if ((err = cipher_is_valid(cbc->cipher)) != CRYPT_OK) {
44 return err;
45 }
46
47 /* is blocklen valid? */
48 if (cbc->blocklen < 1 || cbc->blocklen > (int)sizeof(cbc->IV)) {
49 return CRYPT_INVALID_ARG;
50 }
51
52 if (len % cbc->blocklen) {
53 return CRYPT_INVALID_ARG;
54 }
55 #ifdef LTC_FAST
56 if (cbc->blocklen % sizeof(LTC_FAST_TYPE)) {
57 return CRYPT_INVALID_ARG;
58 }
59 #endif
60
61 if (cipher_descriptor[cbc->cipher].accel_cbc_decrypt != NULL) {
62 return cipher_descriptor[cbc->cipher].accel_cbc_decrypt(ct, pt, len / cbc->blocklen, cbc->IV, &cbc->key);
63 } else {
64 while (len) {
65 /* decrypt */
66 if ((err = cipher_descriptor[cbc->cipher].ecb_decrypt(ct, tmp, &cbc->key)) != CRYPT_OK) {
67 return err;
68 }
69
70 /* xor IV against plaintext */
71 #if defined(LTC_FAST)
72 for (x = 0; x < cbc->blocklen; x += sizeof(LTC_FAST_TYPE)) {
73 tmpy = *((LTC_FAST_TYPE*)((unsigned char *)cbc->IV + x)) ^ *((LTC_FAST_TYPE*)((unsigned char *)tmp + x));
74 *((LTC_FAST_TYPE*)((unsigned char *)cbc->IV + x)) = *((LTC_FAST_TYPE*)((unsigned char *)ct + x));
75 *((LTC_FAST_TYPE*)((unsigned char *)pt + x)) = tmpy;
76 }
77 #else
78 for (x = 0; x < cbc->blocklen; x++) {
79 tmpy = tmp[x] ^ cbc->IV[x];
80 cbc->IV[x] = ct[x];
81 pt[x] = tmpy;
82 }
83 #endif
84
85 ct += cbc->blocklen;
86 pt += cbc->blocklen;
87 len -= cbc->blocklen;
88 }
89 }
90 return CRYPT_OK;
91 }
92
93 #endif
94
95 /* $Source: /cvs/libtom/libtomcrypt/src/modes/cbc/cbc_decrypt.c,v $ */
96 /* $Revision: 1.15 $ */
97 /* $Date: 2006/11/21 00:18:23 $ */
98