1/*
2 *  cchmac_init.c
3 *  corecrypto
4 *
5 *  Created by Michael Brouwer on 12/7/10.
6 *  Copyright 2010,2011 Apple Inc. All rights reserved.
7 *
8 */
9
10#include <corecrypto/cchmac.h>
11#include <corecrypto/ccn.h>
12#include <pexpert/pexpert.h>
13
14/* The HMAC_<DIG> transform looks like:
15   <DIG> (K XOR opad || <DIG> (K XOR ipad || text))
16   Where K is a n byte key
17   ipad is the byte 0x36 repeated 64 times.
18   opad is the byte 0x5c repeated 64 times.
19   text is the data being protected.
20 */
21void cchmac_init(const struct ccdigest_info *di, cchmac_ctx_t hc,
22                 unsigned long key_len, const void *key_data) {
23    const unsigned char *key = key_data;
24
25    /* Set cchmac_data(di, hc) to key ^ opad. */
26    unsigned long byte = 0;
27	if (key_len <= di->block_size) {
28        for (;byte < key_len; ++byte) {
29            cchmac_data(di, hc)[byte] = key[byte] ^ 0x5c;
30        }
31    } else {
32        /* Key is longer than di->block size, reset it to key=digest(key) */
33        ccdigest_init(di, cchmac_digest_ctx(di, hc));
34        ccdigest_update(di, cchmac_digest_ctx(di, hc), key_len, key);
35        ccdigest_final(di, cchmac_digest_ctx(di, hc), cchmac_data(di, hc));
36        key_len = di->output_size;
37        for (;byte < key_len; ++byte) {
38            cchmac_data(di, hc)[byte] ^= 0x5c;
39        }
40    }
41    /* Fill remainder of cchmac_data(di, hc) with opad. */
42	if (key_len < di->block_size) {
43		CC_MEMSET(cchmac_data(di, hc) + key_len, 0x5c, di->block_size - key_len);
44	}
45
46    /* Set cchmac_ostate32(di, hc) to the state of the first round of the
47       outer digest. */
48    ccdigest_copy_state(di, cchmac_ostate32(di, hc), di->initial_state);
49    di->compress(cchmac_ostate(di, hc), 1, cchmac_data(di, hc));
50
51    /* Set cchmac_data(di, hc) to key ^ ipad. */
52    for (byte = 0; byte < di->block_size; ++byte) {
53        cchmac_data(di, hc)[byte] ^= (0x5c ^ 0x36);
54    }
55    ccdigest_copy_state(di, cchmac_istate32(di, hc), di->initial_state);
56    di->compress(cchmac_istate(di, hc), 1, cchmac_data(di, hc));
57    cchmac_num(di, hc) = 0;
58    cchmac_nbits(di, hc) = di->block_size * 8;
59}
60