Codebase list libcryptx-perl / v0.023 src / ltc / modes / cbc / cbc_decrypt.c
v0.023

Tree @v0.023 (Download .tar.gz)

cbc_decrypt.c @v0.023 — raw · history · blame 

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
/* LibTomCrypt, modular cryptographic library -- Tom St Denis
 *
 * LibTomCrypt is a library that provides various cryptographic
 * algorithms in a highly modular and flexible manner.
 *
 * The library is free for all purposes without any express
 * guarantee it works.
 *
 * Tom St Denis, tomstdenis@gmail.com, http://libtom.org
 */
#include "tomcrypt.h"

/**
   @file cbc_decrypt.c
   CBC implementation, encrypt block, Tom St Denis
*/


#ifdef LTC_CBC_MODE

/**
  CBC decrypt
  @param ct     Ciphertext
  @param pt     [out] Plaintext
  @param len    The number of bytes to process (must be multiple of block length)
  @param cbc    CBC state
  @return CRYPT_OK if successful
*/
int cbc_decrypt(const unsigned char *ct, unsigned char *pt, unsigned long len, symmetric_CBC *cbc)
{
   int x, err;
   unsigned char tmp[16];
#ifdef LTC_FAST
   LTC_FAST_TYPE tmpy;
#else
   unsigned char tmpy;
#endif

   LTC_ARGCHK(pt  != NULL);
   LTC_ARGCHK(ct  != NULL);
   LTC_ARGCHK(cbc != NULL);

   if ((err = cipher_is_valid(cbc->cipher)) != CRYPT_OK) {
       return err;
   }

   /* is blocklen valid? */
   if (cbc->blocklen < 1 || cbc->blocklen > (int)sizeof(cbc->IV)) {
      return CRYPT_INVALID_ARG;
   }

   if (len % cbc->blocklen) {
      return CRYPT_INVALID_ARG;
   }
#ifdef LTC_FAST
   if (cbc->blocklen % sizeof(LTC_FAST_TYPE)) {
      return CRYPT_INVALID_ARG;
   }
#endif

   if (cipher_descriptor[cbc->cipher].accel_cbc_decrypt != NULL) {
      return cipher_descriptor[cbc->cipher].accel_cbc_decrypt(ct, pt, len / cbc->blocklen, cbc->IV, &cbc->key);
   } else {
      while (len) {
         /* decrypt */
         if ((err = cipher_descriptor[cbc->cipher].ecb_decrypt(ct, tmp, &cbc->key)) != CRYPT_OK) {
            return err;
         }

         /* xor IV against plaintext */
         #if defined(LTC_FAST)
        for (x = 0; x < cbc->blocklen; x += sizeof(LTC_FAST_TYPE)) {
            tmpy = *((LTC_FAST_TYPE*)((unsigned char *)cbc->IV + x)) ^ *((LTC_FAST_TYPE*)((unsigned char *)tmp + x));
       *((LTC_FAST_TYPE*)((unsigned char *)cbc->IV + x)) = *((LTC_FAST_TYPE*)((unsigned char *)ct + x));
       *((LTC_FAST_TYPE*)((unsigned char *)pt + x)) = tmpy;
        }
    #else
            for (x = 0; x < cbc->blocklen; x++) {
               tmpy       = tmp[x] ^ cbc->IV[x];
               cbc->IV[x] = ct[x];
               pt[x]      = tmpy;
            }
    #endif

         ct  += cbc->blocklen;
         pt  += cbc->blocklen;
         len -= cbc->blocklen;
      }
   }
   return CRYPT_OK;
}

#endif

/* $Source$ */
/* $Revision$ */
/* $Date$ */