librsync  2.3.0
checksum.c
1 /*= -*- c-basic-offset: 4; indent-tabs-mode: nil; -*-
2  *
3  * librsync -- the library for network deltas
4  *
5  * Copyright (C) 1999, 2000, 2001 by Martin Pool <mbp@sourcefrog.net>
6  * Copyright (C) 1996 by Andrew Tridgell
7  * Copyright (C) 1996 by Paul Mackerras
8  *
9  * This program is free software; you can redistribute it and/or modify
10  * it under the terms of the GNU Lesser General Public License as published by
11  * the Free Software Foundation; either version 2.1 of the License, or
12  * (at your option) any later version.
13  *
14  * This program is distributed in the hope that it will be useful,
15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17  * GNU Lesser General Public License for more details.
18  *
19  * You should have received a copy of the GNU Lesser General Public License
20  * along with this program; if not, write to the Free Software
21  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
22  */
23 
24 #include "config.h"
25 #include "checksum.h"
26 #include "blake2.h"
27 
28 LIBRSYNC_EXPORT const int RS_MD4_SUM_LENGTH = 16;
29 LIBRSYNC_EXPORT const int RS_BLAKE2_SUM_LENGTH = 32;
30 
31 /** A simple 32bit checksum that can be incrementally updated. */
32 rs_weak_sum_t rs_calc_weak_sum(weaksum_kind_t kind, void const *buf, size_t len)
33 {
34  if (kind == RS_ROLLSUM) {
35  Rollsum sum;
36  RollsumInit(&sum);
37  RollsumUpdate(&sum, buf, len);
38  return RollsumDigest(&sum);
39  } else {
40  rabinkarp_t sum;
41  rabinkarp_init(&sum);
42  rabinkarp_update(&sum, buf, len);
43  return rabinkarp_digest(&sum);
44  }
45 }
46 
47 /** Calculate and store into SUM a strong checksum.
48  *
49  * In plain rsync, the checksum is perturbed by a seed value. This is used when
50  * retrying a failed transmission: we've discovered that the hashes collided at
51  * some point, so we're going to try again with different hashes to see if we
52  * can get it right. (Check tridge's thesis for details and to see if that's
53  * correct.)
54  *
55  * Since we can't retry I'm not sure if it's very useful for librsync, except
56  * perhaps as protection against hash collision attacks. */
57 void rs_calc_strong_sum(strongsum_kind_t kind, void const *buf, size_t len,
58  rs_strong_sum_t *sum)
59 {
60  if (kind == RS_MD4) {
61  rs_mdfour((unsigned char *)sum, buf, len);
62  } else {
63  blake2b_state ctx;
64  blake2b_init(&ctx, RS_MAX_STRONG_SUM_LENGTH);
65  blake2b_update(&ctx, (const uint8_t *)buf, len);
66  blake2b_final(&ctx, (uint8_t *)sum, RS_MAX_STRONG_SUM_LENGTH);
67  }
68 }