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comparison src/encauth/ocb/ocb_decrypt.c @ 192:9cc34777b479 libtomcrypt

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propagate from branch 'au.asn.ucc.matt.ltc-orig' (head 9ba8f01f44320e9cb9f19881105ae84f84a43ea9) to branch 'au.asn.ucc.matt.dropbear.ltc' (head dbf51c569bc34956ad948e4cc87a0eeb2170b768)
author Matt Johnston <matt@ucc.asn.au>
date Sun, 08 May 2005 06:36:47 +0000
parents 1c15b283127b
children 39d5d58461d6
comparison
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164:cd1143579f00 192:9cc34777b479
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 /**
13 @file ocb_decrypt.c
14 OCB implementation, decrypt data, by Tom St Denis
15 */
16 #include "tomcrypt.h"
17
18 #ifdef OCB_MODE
19
20 /**
21 Decrypt a block with OCB.
22 @param ocb The OCB state
23 @param ct The ciphertext (length of the block size of the block cipher)
24 @param pt [out] The plaintext (length of ct)
25 @return CRYPT_OK if successful
26 */
27 int ocb_decrypt(ocb_state *ocb, const unsigned char *ct, unsigned char *pt)
28 {
29 unsigned char Z[MAXBLOCKSIZE], tmp[MAXBLOCKSIZE];
30 int err, x;
31
32 LTC_ARGCHK(ocb != NULL);
33 LTC_ARGCHK(pt != NULL);
34 LTC_ARGCHK(ct != NULL);
35
36 /* check if valid cipher */
37 if ((err = cipher_is_valid(ocb->cipher)) != CRYPT_OK) {
38 return err;
39 }
40 LTC_ARGCHK(cipher_descriptor[ocb->cipher].ecb_decrypt != NULL);
41
42 /* check length */
43 if (ocb->block_len != cipher_descriptor[ocb->cipher].block_length) {
44 return CRYPT_INVALID_ARG;
45 }
46
47 /* Get Z[i] value */
48 ocb_shift_xor(ocb, Z);
49
50 /* xor ct in, encrypt, xor Z out */
51 for (x = 0; x < ocb->block_len; x++) {
52 tmp[x] = ct[x] ^ Z[x];
53 }
54 cipher_descriptor[ocb->cipher].ecb_decrypt(tmp, pt, &ocb->key);
55 for (x = 0; x < ocb->block_len; x++) {
56 pt[x] ^= Z[x];
57 }
58
59 /* compute checksum */
60 for (x = 0; x < ocb->block_len; x++) {
61 ocb->checksum[x] ^= pt[x];
62 }
63
64
65 #ifdef LTC_CLEAN_STACK
66 zeromem(Z, sizeof(Z));
67 zeromem(tmp, sizeof(tmp));
68 #endif
69 return CRYPT_OK;
70 }
71
72 #endif
73