1 // SPDX-License-Identifier: BSD-2-Clause
2 /* LibTomCrypt, modular cryptographic library -- Tom St Denis
3 *
4 * LibTomCrypt is a library that provides various cryptographic
5 * algorithms in a highly modular and flexible manner.
6 *
7 * The library is free for all purposes without any express
8 * guarantee it works.
9 */
10
11 /**
12 @file ocb3_encrypt_last.c
13 OCB implementation, internal helper, by Karel Miko
14 */
15 #include "tomcrypt_private.h"
16
17 #ifdef LTC_OCB3_MODE
18
19 /**
20 Finish an OCB (encryption) stream
21 @param ocb The OCB state
22 @param pt The remaining plaintext
23 @param ptlen The length of the plaintext (octets)
24 @param ct [out] The output buffer
25 @return CRYPT_OK if successful
26 */
ocb3_encrypt_last(ocb3_state * ocb,const unsigned char * pt,unsigned long ptlen,unsigned char * ct)27 int ocb3_encrypt_last(ocb3_state *ocb, const unsigned char *pt, unsigned long ptlen, unsigned char *ct)
28 {
29 unsigned char iOffset_star[MAXBLOCKSIZE];
30 unsigned char iPad[MAXBLOCKSIZE];
31 int err, x, full_blocks, full_blocks_len, last_block_len;
32
33 LTC_ARGCHK(ocb != NULL);
34 if (pt == NULL) LTC_ARGCHK(ptlen == 0);
35 if (ptlen != 0) {
36 LTC_ARGCHK(pt != NULL);
37 LTC_ARGCHK(ct != NULL);
38 }
39
40 if ((err = cipher_is_valid(ocb->cipher)) != CRYPT_OK) {
41 goto LBL_ERR;
42 }
43
44 full_blocks = ptlen/ocb->block_len;
45 full_blocks_len = full_blocks * ocb->block_len;
46 last_block_len = ptlen - full_blocks_len;
47
48 /* process full blocks first */
49 if (full_blocks>0) {
50 if ((err = ocb3_encrypt(ocb, pt, full_blocks_len, ct)) != CRYPT_OK) {
51 goto LBL_ERR;
52 }
53 }
54
55 /* at this point: m = ocb->block_index (last block index), Offset_m = ocb->Offset_current */
56
57 if (last_block_len>0) {
58 /* Offset_* = Offset_m xor L_* */
59 ocb3_int_xor_blocks(iOffset_star, ocb->Offset_current, ocb->L_star, ocb->block_len);
60
61 /* Pad = ENCIPHER(K, Offset_*) */
62 if ((err = cipher_descriptor[ocb->cipher]->ecb_encrypt(iOffset_star, iPad, &ocb->key)) != CRYPT_OK) {
63 goto LBL_ERR;
64 }
65
66 /* C_* = P_* xor Pad[1..bitlen(P_*)] */
67 ocb3_int_xor_blocks(ct+full_blocks_len, pt+full_blocks_len, iPad, last_block_len);
68
69 /* Checksum_* = Checksum_m xor (P_* || 1 || zeros(127-bitlen(P_*))) */
70 ocb3_int_xor_blocks(ocb->checksum, ocb->checksum, pt+full_blocks_len, last_block_len);
71 for(x=last_block_len; x<ocb->block_len; x++) {
72 if (x == last_block_len) {
73 ocb->checksum[x] ^= 0x80;
74 } else {
75 ocb->checksum[x] ^= 0x00;
76 }
77 }
78
79 /* Tag = ENCIPHER(K, Checksum_* xor Offset_* xor L_$) xor HASH(K,A) */
80 /* at this point we calculate only: Tag_part = ENCIPHER(K, Checksum_* xor Offset_* xor L_$) */
81 for(x=0; x<ocb->block_len; x++) {
82 ocb->tag_part[x] = (ocb->checksum[x] ^ iOffset_star[x]) ^ ocb->L_dollar[x];
83 }
84 if ((err = cipher_descriptor[ocb->cipher]->ecb_encrypt(ocb->tag_part, ocb->tag_part, &ocb->key)) != CRYPT_OK) {
85 goto LBL_ERR;
86 }
87 } else {
88 /* Tag = ENCIPHER(K, Checksum_m xor Offset_m xor L_$) xor HASH(K,A) */
89 /* at this point we calculate only: Tag_part = ENCIPHER(K, Checksum_m xor Offset_m xor L_$) */
90 for(x=0; x<ocb->block_len; x++) {
91 ocb->tag_part[x] = (ocb->checksum[x] ^ ocb->Offset_current[x]) ^ ocb->L_dollar[x];
92 }
93 if ((err = cipher_descriptor[ocb->cipher]->ecb_encrypt(ocb->tag_part, ocb->tag_part, &ocb->key)) != CRYPT_OK) {
94 goto LBL_ERR;
95 }
96 }
97
98 err = CRYPT_OK;
99
100 LBL_ERR:
101 #ifdef LTC_CLEAN_STACK
102 zeromem(iOffset_star, MAXBLOCKSIZE);
103 zeromem(iPad, MAXBLOCKSIZE);
104 #endif
105
106 return err;
107 }
108
109 #endif
110
111 /* ref: $Format:%D$ */
112 /* git commit: $Format:%H$ */
113 /* commit time: $Format:%ai$ */
114