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comparison ocb_decrypt.c @ 3:7faae8f46238 libtomcrypt-orig

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Branch renaming
author Matt Johnston <matt@ucc.asn.au>
date Mon, 31 May 2004 18:25:41 +0000
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children 6362d3854bb4
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-1:000000000000 3:7faae8f46238
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, [email protected], http://libtomcrypt.org
10 */
11
12 /* OCB Implementation by Tom St Denis */
13 #include "mycrypt.h"
14
15 #ifdef OCB_MODE
16
17 int ocb_decrypt(ocb_state *ocb, const unsigned char *ct, unsigned char *pt)
18 {
19 unsigned char Z[MAXBLOCKSIZE], tmp[MAXBLOCKSIZE];
20 int err, x;
21
22 _ARGCHK(ocb != NULL);
23 _ARGCHK(pt != NULL);
24 _ARGCHK(ct != NULL);
25 if ((err = cipher_is_valid(ocb->cipher)) != CRYPT_OK) {
26 return err;
27 }
28 if (ocb->block_len != cipher_descriptor[ocb->cipher].block_length) {
29 return CRYPT_INVALID_ARG;
30 }
31
32 /* Get Z[i] value */
33 ocb_shift_xor(ocb, Z);
34
35 /* xor ct in, encrypt, xor Z out */
36 for (x = 0; x < ocb->block_len; x++) {
37 tmp[x] = ct[x] ^ Z[x];
38 }
39 cipher_descriptor[ocb->cipher].ecb_decrypt(tmp, pt, &ocb->key);
40 for (x = 0; x < ocb->block_len; x++) {
41 pt[x] ^= Z[x];
42 }
43
44 /* compute checksum */
45 for (x = 0; x < ocb->block_len; x++) {
46 ocb->checksum[x] ^= pt[x];
47 }
48
49
50 #ifdef CLEAN_STACK
51 zeromem(Z, sizeof(Z));
52 zeromem(tmp, sizeof(tmp));
53 #endif
54 return CRYPT_OK;
55 }
56
57 #endif
58