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comparison libtomcrypt/src/encauth/ocb3/ocb3_decrypt_last.c @ 1471:6dba84798cd5

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Update to libtomcrypt 1.18.1, merged with Dropbear changes
author Matt Johnston <matt@ucc.asn.au>
date Fri, 09 Feb 2018 21:44:05 +0800
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1470:8bba51a55704 1471:6dba84798cd5
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
10 /**
11 @file ocb3_decrypt_last.c
12 OCB implementation, internal helper, by Karel Miko
13 */
14 #include "tomcrypt.h"
15
16 #ifdef LTC_OCB3_MODE
17
18 /**
19 Finish an OCB (decryption) stream
20 @param ocb The OCB state
21 @param ct The remaining ciphertext
22 @param ctlen The length of the ciphertext (octets)
23 @param pt [out] The output buffer
24 @return CRYPT_OK if successful
25 */
26 int ocb3_decrypt_last(ocb3_state *ocb, const unsigned char *ct, unsigned long ctlen, unsigned char *pt)
27 {
28 unsigned char iOffset_star[MAXBLOCKSIZE];
29 unsigned char iPad[MAXBLOCKSIZE];
30 int err, x, full_blocks, full_blocks_len, last_block_len;
31
32 LTC_ARGCHK(ocb != NULL);
33 if (ct == NULL) LTC_ARGCHK(ctlen == 0);
34 if (ctlen != 0) {
35 LTC_ARGCHK(ct != NULL);
36 LTC_ARGCHK(pt != NULL);
37 }
38
39 if ((err = cipher_is_valid(ocb->cipher)) != CRYPT_OK) {
40 goto LBL_ERR;
41 }
42
43 full_blocks = ctlen/ocb->block_len;
44 full_blocks_len = full_blocks * ocb->block_len;
45 last_block_len = ctlen - full_blocks_len;
46
47 /* process full blocks first */
48 if (full_blocks>0) {
49 if ((err = ocb3_decrypt(ocb, ct, full_blocks_len, pt)) != CRYPT_OK) {
50 goto LBL_ERR;
51 }
52 }
53
54 if (last_block_len>0) {
55 /* Offset_* = Offset_m xor L_* */
56 ocb3_int_xor_blocks(iOffset_star, ocb->Offset_current, ocb->L_star, ocb->block_len);
57
58 /* Pad = ENCIPHER(K, Offset_*) */
59 if ((err = cipher_descriptor[ocb->cipher].ecb_encrypt(iOffset_star, iPad, &ocb->key)) != CRYPT_OK) {
60 goto LBL_ERR;
61 }
62
63 /* P_* = C_* xor Pad[1..bitlen(C_*)] */
64 ocb3_int_xor_blocks(pt+full_blocks_len, (unsigned char *)ct+full_blocks_len, iPad, last_block_len);
65
66 /* Checksum_* = Checksum_m xor (P_* || 1 || zeros(127-bitlen(P_*))) */
67 ocb3_int_xor_blocks(ocb->checksum, ocb->checksum, pt+full_blocks_len, last_block_len);
68 for(x=last_block_len; x<ocb->block_len; x++) {
69 if (x == last_block_len)
70 ocb->checksum[x] ^= 0x80;
71 else
72 ocb->checksum[x] ^= 0x00;
73 }
74
75 /* Tag = ENCIPHER(K, Checksum_* xor Offset_* xor L_$) xor HASH(K,A) */
76 /* at this point we calculate only: Tag_part = ENCIPHER(K, Checksum_* xor Offset_* xor L_$) */
77 for(x=0; x<ocb->block_len; x++) {
78 ocb->tag_part[x] = (ocb->checksum[x] ^ iOffset_star[x]) ^ ocb->L_dollar[x];
79 }
80 if ((err = cipher_descriptor[ocb->cipher].ecb_encrypt(ocb->tag_part, ocb->tag_part, &ocb->key)) != CRYPT_OK) {
81 goto LBL_ERR;
82 }
83 }
84 else {
85 /* Tag = ENCIPHER(K, Checksum_m xor Offset_m xor L_$) xor HASH(K,A) */
86 /* at this point we calculate only: Tag_part = ENCIPHER(K, Checksum_m xor Offset_m xor L_$) */
87 for(x=0; x<ocb->block_len; x++) {
88 ocb->tag_part[x] = (ocb->checksum[x] ^ ocb->Offset_current[x]) ^ ocb->L_dollar[x];
89 }
90 if ((err = cipher_descriptor[ocb->cipher].ecb_encrypt(ocb->tag_part, ocb->tag_part, &ocb->key)) != CRYPT_OK) {
91 goto LBL_ERR;
92 }
93 }
94
95 err = CRYPT_OK;
96
97 LBL_ERR:
98 #ifdef LTC_CLEAN_STACK
99 zeromem(iOffset_star, MAXBLOCKSIZE);
100 zeromem(iPad, MAXBLOCKSIZE);
101 #endif
102
103 return err;
104 }
105
106 #endif
107
108 /* ref: $Format:%D$ */
109 /* git commit: $Format:%H$ */
110 /* commit time: $Format:%ai$ */