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/* $OpenBSD: ip6_id.c,v 1.9 2014/11/18 02:37:31 tedu Exp $ */
/* $NetBSD: ip6_id.c,v 1.7 2003/09/13 21:32:59 itojun Exp $ */
/* $KAME: ip6_id.c,v 1.8 2003/09/06 13:41:06 itojun Exp $ */
/*
* Copyright (C) 2003 WIDE Project.
* All rights reserved.
*
* 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 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 PROJECT 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 PROJECT 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 1998 Niels Provos <provos@citi.umich.edu>
* All rights reserved.
*
* Theo de Raadt <deraadt@openbsd.org> came up with the idea of using
* such a mathematical system to generate more random (yet non-repeating)
* ids to solve the resolver/named problem. But Niels designed the
* actual system based on the constraints.
*
* 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.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
*/
/*
* seed = random (bits - 1) bit
* n = prime, g0 = generator to n,
* j = random so that gcd(j,n-1) == 1
* g = g0^j mod n will be a generator again.
*
* X[0] = random seed.
* X[n] = a*X[n-1]+b mod m is a Linear Congruential Generator
* with a = 7^(even random) mod m,
* b = random with gcd(b,m) == 1
* m = constant and a maximal period of m-1.
*
* The transaction id is determined by:
* id[n] = seed xor (g^X[n] mod n)
*
* Effectivly the id is restricted to the lower (bits - 1) bits, thus
* yielding two different cycles by toggling the msb on and off.
* This avoids reuse issues caused by reseeding.
*/
#include <sys/types.h>
#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/socket.h>
#include <sys/systm.h>
#include <net/if.h>
#include <netinet/in.h>
#include <netinet/ip6.h>
#include <netinet6/ip6_var.h>
struct randomtab {
const int ru_bits; /* resulting bits */
const long ru_out; /* Time after wich will be reseeded */
const u_int32_t ru_max; /* Uniq cycle, avoid blackjack prediction */
const u_int32_t ru_gen; /* Starting generator */
const u_int32_t ru_n; /* ru_n: prime, ru_n - 1: product of pfacts[] */
const u_int32_t ru_agen; /* determine ru_a as ru_agen^(2*rand) */
const u_int32_t ru_m; /* ru_m = 2^x*3^y */
const u_int32_t pfacts[4]; /* factors of ru_n */
u_int32_t ru_counter;
u_int32_t ru_msb;
u_int32_t ru_x;
u_int32_t ru_seed, ru_seed2;
u_int32_t ru_a, ru_b;
u_int32_t ru_g;
long ru_reseed;
};
static struct randomtab randomtab_20 = {
20, /* resulting bits */
180, /* Time after wich will be reseeded */
200000, /* Uniq cycle, avoid blackjack prediction */
2, /* Starting generator */
524269, /* RU_N-1 = 2^2*3^2*14563 */
7, /* determine ru_a as RU_AGEN^(2*rand) */
279936, /* RU_M = 2^7*3^7 - don't change */
{ 2, 3, 14563, 0 }, /* factors of ru_n */
};
u_int32_t pmod(u_int32_t, u_int32_t, u_int32_t);
void initid(struct randomtab *);
u_int32_t randomid(struct randomtab *);
/*
* Do a fast modular exponation, returned value will be in the range
* of 0 - (mod-1)
*/
u_int32_t
pmod(u_int32_t gen, u_int32_t expo, u_int32_t mod)
{
u_int64_t s, t, u;
s = 1;
t = gen;
u = expo;
while (u) {
if (u & 1)
s = (s * t) % mod;
u >>= 1;
t = (t * t) % mod;
}
return (s);
}
/*
* Initializes the seed and chooses a suitable generator. Also toggles
* the msb flag. The msb flag is used to generate two distinct
* cycles of random numbers and thus avoiding reuse of ids.
*
* This function is called from id_randomid() when needed, an
* application does not have to worry about it.
*/
void
initid(struct randomtab *p)
{
u_int32_t j, i;
int noprime = 1;
p->ru_x = arc4random_uniform(p->ru_m);
/* (bits - 1) bits of random seed */
p->ru_seed = arc4random() & (~0U >> (32 - p->ru_bits + 1));
p->ru_seed2 = arc4random() & (~0U >> (32 - p->ru_bits + 1));
/* Determine the LCG we use */
p->ru_b = (arc4random() & (~0U >> (32 - p->ru_bits))) | 1;
p->ru_a = pmod(p->ru_agen,
(arc4random() & (~0U >> (32 - p->ru_bits))) & (~1U), p->ru_m);
while (p->ru_b % 3 == 0)
p->ru_b += 2;
j = arc4random_uniform(p->ru_n);
/*
* Do a fast gcd(j, RU_N - 1), so we can find a j with
* gcd(j, RU_N - 1) == 1, giving a new generator for
* RU_GEN^j mod RU_N
*/
while (noprime) {
for (i = 0; p->pfacts[i] > 0; i++)
if (j % p->pfacts[i] == 0)
break;
if (p->pfacts[i] == 0)
noprime = 0;
else
j = (j + 1) % p->ru_n;
}
p->ru_g = pmod(p->ru_gen, j, p->ru_n);
p->ru_counter = 0;
p->ru_reseed = time_second + p->ru_out;
p->ru_msb = p->ru_msb ? 0 : (1U << (p->ru_bits - 1));
}
u_int32_t
randomid(struct randomtab *p)
{
int i, n;
if (p->ru_counter >= p->ru_max || time_second > p->ru_reseed)
initid(p);
/* Skip a random number of ids */
n = arc4random() & 0x3;
if (p->ru_counter + n >= p->ru_max)
initid(p);
for (i = 0; i <= n; i++) {
/* Linear Congruential Generator */
p->ru_x = (u_int32_t)((u_int64_t)p->ru_a * p->ru_x + p->ru_b) % p->ru_m;
}
p->ru_counter += i;
return (p->ru_seed ^ pmod(p->ru_g, p->ru_seed2 + p->ru_x, p->ru_n)) |
p->ru_msb;
}
u_int32_t
ip6_randomflowlabel(void)
{
return randomid(&randomtab_20) & 0xfffff;
}
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