librsync  2.0.1
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 <[email protected]>
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 
26 #include <assert.h>
27 #include <stdlib.h>
28 #include <stdio.h>
29 
30 #include "librsync.h"
31 #include "checksum.h"
32 #include "blake2.h"
33 
34 
35 /* This can possibly be used to restart the checksum system in the
36  * case where we detected corruption. I'm not sure yet how to make
37  * this useful in librsync. */
38 int checksum_seed = 0;
39 
40 /*
41  * A simple 32 bit checksum that can be updated from either end
42  * (inspired by Mark Adler's Adler-32 checksum)
43  */
44 unsigned int rs_calc_weak_sum(void const *p, int len)
45 {
46  int i;
47  unsigned s1, s2;
48  unsigned char const *buf = (unsigned char const *) p;
49 
50  s1 = s2 = 0;
51  for (i = 0; i < (len - 4); i += 4) {
52  s2 += 4 * (s1 + buf[i]) + 3 * buf[i + 1] +
53  2 * buf[i + 2] + buf[i + 3] + 10 * RS_CHAR_OFFSET;
54  s1 += (buf[i + 0] + buf[i + 1] + buf[i + 2] + buf[i + 3] +
55  4 * RS_CHAR_OFFSET);
56  }
57  for (; i < len; i++) {
58  s1 += (buf[i] + RS_CHAR_OFFSET);
59  s2 += s1;
60  }
61  return (s1 & 0xffff) + (s2 << 16);
62 }
63 
64 
65 /**
66  * Calculate and store into SUM a strong MD4 checksum of the file
67  * blocks seen so far.
68  *
69  * In plain rsync, the checksum is perturbed by a seed value. This is
70  * used when retrying a failed transmission: we've discovered that the
71  * hashes collided at some point, so we're going to try again with
72  * different hashes to see if we can get it right. (Check tridge's
73  * thesis for details and to see if that's correct.)
74  *
75  * Since we can't retry a web transaction I'm not sure if it's very
76  * useful in rproxy.
77  */
78 void rs_calc_md4_sum(void const *buf, size_t len, rs_strong_sum_t *sum)
79 {
80  rs_mdfour((unsigned char *) sum, buf, len);
81 }
82 
83 void rs_calc_blake2_sum(void const *buf, size_t len, rs_strong_sum_t *sum)
84 {
85  blake2b_state ctx;
86  blake2b_init(&ctx, RS_MAX_STRONG_SUM_LENGTH);
87  blake2b_update(&ctx, (const uint8_t *)buf, len);
88  blake2b_final(&ctx, (uint8_t *)sum, RS_MAX_STRONG_SUM_LENGTH);
89 }
Public header for librsync.