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
|
/* 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.
*/
/**
@file ocb3_decrypt.c
OCB implementation, decrypt data, by Tom St Denis
*/
#include "tomcrypt.h"
#ifdef LTC_OCB3_MODE
/**
Decrypt blocks of ciphertext with OCB
@param ocb The OCB state
@param ct The ciphertext (length multiple of the block size of the block cipher)
@param ctlen The length of the input (octets)
@param pt [out] The plaintext (length of ct)
@return CRYPT_OK if successful
*/
int ocb3_decrypt(ocb3_state *ocb, const unsigned char *ct, unsigned long ctlen, unsigned char *pt)
{
unsigned char tmp[MAXBLOCKSIZE];
int err, i, full_blocks;
unsigned char *pt_b, *ct_b;
LTC_ARGCHK(ocb != NULL);
if (ctlen == 0) return CRYPT_OK; /* no data, nothing to do */
LTC_ARGCHK(ct != NULL);
LTC_ARGCHK(pt != NULL);
if ((err = cipher_is_valid(ocb->cipher)) != CRYPT_OK) {
return err;
}
if (ocb->block_len != cipher_descriptor[ocb->cipher].block_length) {
return CRYPT_INVALID_ARG;
}
if (ctlen % ocb->block_len) { /* ctlen has to bu multiple of block_len */
return CRYPT_INVALID_ARG;
}
full_blocks = ctlen/ocb->block_len;
for(i=0; i<full_blocks; i++) {
pt_b = (unsigned char *)pt+i*ocb->block_len;
ct_b = (unsigned char *)ct+i*ocb->block_len;
/* ocb->Offset_current[] = ocb->Offset_current[] ^ Offset_{ntz(block_index)} */
ocb3_int_xor_blocks(ocb->Offset_current, ocb->Offset_current, ocb->L_[ocb3_int_ntz(ocb->block_index)], ocb->block_len);
/* tmp[] = ct[] XOR ocb->Offset_current[] */
ocb3_int_xor_blocks(tmp, ct_b, ocb->Offset_current, ocb->block_len);
/* decrypt */
if ((err = cipher_descriptor[ocb->cipher].ecb_decrypt(tmp, tmp, &ocb->key)) != CRYPT_OK) {
goto LBL_ERR;
}
/* pt[] = tmp[] XOR ocb->Offset_current[] */
ocb3_int_xor_blocks(pt_b, tmp, ocb->Offset_current, ocb->block_len);
/* ocb->checksum[] = ocb->checksum[] XOR pt[] */
ocb3_int_xor_blocks(ocb->checksum, ocb->checksum, pt_b, ocb->block_len);
ocb->block_index++;
}
err = CRYPT_OK;
LBL_ERR:
#ifdef LTC_CLEAN_STACK
zeromem(tmp, sizeof(tmp));
#endif
return err;
}
#endif
/* ref: $Format:%D$ */
/* git commit: $Format:%H$ */
/* commit time: $Format:%ai$ */
|
