1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis */
2 /* SPDX-License-Identifier: Unlicense */
3
4 /**
5 @file ocb3_done.c
6 OCB implementation, INTERNAL ONLY helper, by Tom St Denis
7 */
8 #include "tomcrypt_private.h"
9
10 #ifdef LTC_OCB3_MODE
11
12 /**
13 Finish OCB processing and compute the tag
14 @param ocb The OCB state
15 @param tag [out] The destination for the authentication tag
16 @param taglen [in/out] The max size and resulting size of the authentication tag
17 @return CRYPT_OK if successful
18 */
ocb3_done(ocb3_state * ocb,unsigned char * tag,unsigned long * taglen)19 int ocb3_done(ocb3_state *ocb, unsigned char *tag, unsigned long *taglen)
20 {
21 unsigned char tmp[MAXBLOCKSIZE];
22 int err, x;
23
24 LTC_ARGCHK(ocb != NULL);
25 LTC_ARGCHK(tag != NULL);
26 LTC_ARGCHK(taglen != NULL);
27 if ((err = cipher_is_valid(ocb->cipher)) != CRYPT_OK) {
28 goto LBL_ERR;
29 }
30
31 /* check taglen */
32 if ((int)*taglen < ocb->tag_len) {
33 *taglen = (unsigned long)ocb->tag_len;
34 return CRYPT_BUFFER_OVERFLOW;
35 }
36
37 /* finalize AAD processing */
38
39 if (ocb->adata_buffer_bytes>0) {
40 /* Offset_* = Offset_m xor L_* */
41 ocb3_int_xor_blocks(ocb->aOffset_current, ocb->aOffset_current, ocb->L_star, ocb->block_len);
42
43 /* CipherInput = (A_* || 1 || zeros(127-bitlen(A_*))) xor Offset_* */
44 ocb3_int_xor_blocks(tmp, ocb->adata_buffer, ocb->aOffset_current, ocb->adata_buffer_bytes);
45 for(x=ocb->adata_buffer_bytes; x<ocb->block_len; x++) {
46 if (x == ocb->adata_buffer_bytes) {
47 tmp[x] = 0x80 ^ ocb->aOffset_current[x];
48 }
49 else {
50 tmp[x] = 0x00 ^ ocb->aOffset_current[x];
51 }
52 }
53
54 /* Sum = Sum_m xor ENCIPHER(K, CipherInput) */
55 if ((err = cipher_descriptor[ocb->cipher]->ecb_encrypt(tmp, tmp, &ocb->key)) != CRYPT_OK) {
56 goto LBL_ERR;
57 }
58 ocb3_int_xor_blocks(ocb->aSum_current, ocb->aSum_current, tmp, ocb->block_len);
59 }
60
61 /* finalize TAG computing */
62
63 /* at this point ocb->aSum_current = HASH(K, A) */
64 /* tag = tag ^ HASH(K, A) */
65 ocb3_int_xor_blocks(tmp, ocb->tag_part, ocb->aSum_current, ocb->block_len);
66
67 /* copy tag bytes */
68 for(x = 0; x < ocb->tag_len; x++) tag[x] = tmp[x];
69 *taglen = (unsigned long)ocb->tag_len;
70
71 err = CRYPT_OK;
72
73 LBL_ERR:
74 #ifdef LTC_CLEAN_STACK
75 zeromem(tmp, MAXBLOCKSIZE);
76 zeromem(ocb, sizeof(*ocb));
77 #endif
78
79 return err;
80 }
81
82 #endif
83