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*/
29int 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