checksum.c

/*= -*- c-basic-offset: 4; indent-tabs-mode: nil; -*-
 *
 * librsync -- the library for network deltas
 *
 * Copyright (C) 1999, 2000, 2001 by Martin Pool <mbp@sourcefrog.net>
 * Copyright (C) 1996 by Andrew Tridgell
 * Copyright (C) 1996 by Paul Mackerras
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */
 
#include "config.h"             /* IWYU pragma: keep */
#include <stdint.h>
#include "checksum.h"
#include "blake2.h"
#include "librsync_export.h"
 
LIBRSYNC_EXPORT const int RS_MD4_SUM_LENGTH = 16;
LIBRSYNC_EXPORT const int RS_BLAKE2_SUM_LENGTH = 32;
 
/** A simple 32bit checksum that can be incrementally updated. */
rs_weak_sum_t rs_calc_weak_sum(weaksum_kind_t kind, void const *buf, size_t len)
{
    if (kind == RS_ROLLSUM) {
        Rollsum sum;
        RollsumInit(&sum);
        RollsumUpdate(&sum, buf, len);
        return RollsumDigest(&sum);
    } else {
        rabinkarp_t sum;
        rabinkarp_init(&sum);
        rabinkarp_update(&sum, buf, len);
        return rabinkarp_digest(&sum);
    }
}
 
/** Calculate and store into SUM a strong checksum.
 *
 * In plain rsync, the checksum is perturbed by a seed value. This is used when
 * retrying a failed transmission: we've discovered that the hashes collided at
 * some point, so we're going to try again with different hashes to see if we
 * can get it right. (Check tridge's thesis for details and to see if that's
 * correct.)
 *
 * Since we can't retry I'm not sure if it's very useful for librsync, except
 * perhaps as protection against hash collision attacks. */
void rs_calc_strong_sum(strongsum_kind_t kind, void const *buf, size_t len,
                        rs_strong_sum_t *sum)
{
    if (kind == RS_MD4) {
        rs_mdfour((unsigned char *)sum, buf, len);
    } else {
        blake2b_state ctx;
        blake2b_init(&ctx, RS_MAX_STRONG_SUM_LENGTH);
        blake2b_update(&ctx, (const uint8_t *)buf, len);
        blake2b_final(&ctx, (uint8_t *)sum, RS_MAX_STRONG_SUM_LENGTH);
    }
}