toeplitz.c

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Author : tb
Date : 2020-07-17 13:13:36
Hash : ea21b721
Message : Randomize the system stoeplitz key One can prove that the Toeplitz matrix generated from a 16-bit seed is invertible if and only if the seed has odd Boolean parity. Invertibility is necessary and sufficient for the stoeplitz hash to take all 65536 possible values. Generate a system stoeplitz seed of odd parity uniformly at random. This is done by generating a random 16-bit number and then flipping its last bit if it's of even parity. This works since flipping the last bit swaps the numbers of even and odd parity, so we obtain a 2:1 mapping from all 16-bit numbers onto those with odd parity. Implementation of parity via popcount provided by naddy; input from miod, David Higgs, Matthew Martin, Martin Vahlensieck and others. ok dlg

sys/net/toeplitz.c

/* $OpenBSD: toeplitz.c,v 1.8 2020/07/17 13:13:36 tb Exp $ */

/*
 * Copyright (c) 2009 The DragonFly Project.  All rights reserved.
 *
 * This code is derived from software contributed to The DragonFly Project
 * by Sepherosa Ziehau <sepherosa@gmail.com>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name of The DragonFly Project nor the names of its
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific, prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * Copyright (c) 2019 David Gwynne <dlg@openbsd.org>
 * Copyright (c) 2020 Theo Buehler <tb@openbsd.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/sysctl.h>

#include <netinet/in.h>

#include <net/toeplitz.h>

/*
 * symmetric toeplitz
 */

static stoeplitz_key		stoeplitz_keyseed = STOEPLITZ_KEYSEED;
static struct stoeplitz_cache	stoeplitz_syskey_cache;
const struct stoeplitz_cache *const
				stoeplitz_cache = &stoeplitz_syskey_cache; 

/* parity of n16: count (mod 2) of ones in the binary representation. */
int
parity(uint16_t n16)
{
	n16 = ((n16 & 0xaaaa) >> 1) ^ (n16 & 0x5555);
	n16 = ((n16 & 0xcccc) >> 2) ^ (n16 & 0x3333);
	n16 = ((n16 & 0xf0f0) >> 4) ^ (n16 & 0x0f0f);
	n16 = ((n16 & 0xff00) >> 8) ^ (n16 & 0x00ff);

	return (n16);
}

/*
 * The Toeplitz matrix obtained from a seed is invertible if and only if the
 * parity of the seed is 1. Generate such a seed uniformly at random.
 */
stoeplitz_key
stoeplitz_random_seed(void)
{
	stoeplitz_key seed;
       
	seed = arc4random() & UINT16_MAX;
	if (parity(seed) == 0)
		seed ^= 1;

	return (seed);
}

void
stoeplitz_init(void)
{
	stoeplitz_keyseed = stoeplitz_random_seed();
	stoeplitz_cache_init(&stoeplitz_syskey_cache, stoeplitz_keyseed);
}

#define NBSK (NBBY * sizeof(stoeplitz_key))

/*
 * The Toeplitz hash of a 16-bit number considered as a column vector over
 * the field with two elements is calculated as a matrix multiplication with
 * a 16x16 circulant Toeplitz matrix T generated by skey.
 *
 * The first eight columns H of T generate the remaining eight columns using
 * the byteswap operation J = swap16:  T = [H JH].  Thus, the Toeplitz hash of
 * n = [hi lo] is computed via the formula T * n = (H * hi) ^ swap16(H * lo).
 *
 * Therefore the results H * val for all values of a byte are cached in scache.
 */
void
stoeplitz_cache_init(struct stoeplitz_cache *scache, stoeplitz_key skey)
{
	uint16_t column[NBBY];
	unsigned int b, shift, val;

	bzero(column, sizeof(column));

	/* Calculate the first eight columns H of the Toeplitz matrix T. */
	for (b = 0; b < NBBY; ++b)
		column[b] = skey << b | skey >> (NBSK - b);

	/* Cache the results of H * val for all possible values of a byte. */
	for (val = 0; val < 256; ++val) {
		uint16_t res = 0;

		for (b = 0; b < NBBY; ++b) {
			shift = NBBY - b - 1;
			if (val & (1 << shift))
				res ^= column[b];
		}
		scache->bytes[val] = res;
	}
}

uint16_t
stoeplitz_hash_ip4(const struct stoeplitz_cache *scache,
    in_addr_t faddr, in_addr_t laddr)
{
	return (stoeplitz_hash_n32(scache, faddr ^ laddr));
}

uint16_t
stoeplitz_hash_ip4port(const struct stoeplitz_cache *scache,
    in_addr_t faddr, in_addr_t laddr, in_port_t fport, in_port_t lport)
{
	return (stoeplitz_hash_n32(scache, faddr ^ laddr ^ fport ^ lport));
}

#ifdef INET6
uint16_t
stoeplitz_hash_ip6(const struct stoeplitz_cache *scache,
    const struct in6_addr *faddr6, const struct in6_addr *laddr6)
{
	uint32_t n32 = 0;
	size_t i;

	for (i = 0; i < nitems(faddr6->s6_addr32); i++)
		n32 ^= faddr6->s6_addr32[i] ^ laddr6->s6_addr32[i];

	return (stoeplitz_hash_n32(scache, n32));
}

uint16_t
stoeplitz_hash_ip6port(const struct stoeplitz_cache *scache,
    const struct in6_addr *faddr6, const struct in6_addr *laddr6,
    in_port_t fport, in_port_t lport)
{
	uint32_t n32 = 0;
	size_t i;

	for (i = 0; i < nitems(faddr6->s6_addr32); i++)
		n32 ^= faddr6->s6_addr32[i] ^ laddr6->s6_addr32[i];

	n32 ^= fport ^ lport;

	return (stoeplitz_hash_n32(scache, n32));
}
#endif /* INET6 */

void
stoeplitz_to_key(void *key, size_t klen)
{
	uint8_t *k = key;
	uint16_t skey = htons(stoeplitz_keyseed);
	size_t i;

	KASSERT((klen % 2) == 0);

	for (i = 0; i < klen; i += sizeof(skey)) {
		k[i + 0] = skey >> 8;
		k[i + 1] = skey;
	}
}

IABSD.fr/src/sys/net/toeplitz.c

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IABSD.fr/src /sys/net/toeplitz.c