1f44b0a1b5
have already done this, so I have styled the patch on their work:
1) introduce a ip_newid() static inline function that checks
the sysctl and then decides if it should return a sequential
or random IP ID.
2) named the sysctl net.inet.ip.random_id
3) IPv6 flow IDs and fragment IDs are now always random.
Flow IDs and frag IDs are significantly less common in the
IPv6 world (ie. rarely generated per-packet), so there should
be smaller performance concerns.
The sysctl defaults to 0 (sequential IP IDs).
Reviewed by: andre, silby, mlaier, ume
Based on: NetBSD
MFC after: 2 months
266 lines
8.3 KiB
C
266 lines
8.3 KiB
C
/* $KAME: ip6_id.c,v 1.13 2003/09/16 09:11:19 itojun Exp $ */
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/* $OpenBSD: ip_id.c,v 1.6 2002/03/15 18:19:52 millert Exp $ */
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/* $FreeBSD$ */
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/*
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* Copyright (C) 2003 WIDE Project.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the project nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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/*
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* Copyright 1998 Niels Provos <provos@citi.umich.edu>
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* All rights reserved.
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*
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* Theo de Raadt <deraadt@openbsd.org> came up with the idea of using
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* such a mathematical system to generate more random (yet non-repeating)
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* ids to solve the resolver/named problem. But Niels designed the
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* actual system based on the constraints.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by Niels Provos.
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* 4. The name of the author may not be used to endorse or promote products
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* derived from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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/*
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* seed = random (bits - 1) bit
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* n = prime, g0 = generator to n,
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* j = random so that gcd(j,n-1) == 1
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* g = g0^j mod n will be a generator again.
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*
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* X[0] = random seed.
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* X[n] = a*X[n-1]+b mod m is a Linear Congruential Generator
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* with a = 7^(even random) mod m,
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* b = random with gcd(b,m) == 1
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* m = constant and a maximal period of m-1.
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*
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* The transaction id is determined by:
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* id[n] = seed xor (g^X[n] mod n)
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*
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* Effectivly the id is restricted to the lower (bits - 1) bits, thus
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* yielding two different cycles by toggling the msb on and off.
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* This avoids reuse issues caused by reseeding.
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*/
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#include <sys/types.h>
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#include <sys/param.h>
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#include <sys/kernel.h>
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#include <sys/socket.h>
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#include <sys/libkern.h>
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#include <net/if.h>
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#include <net/route.h>
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#include <netinet/in.h>
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#include <netinet/ip6.h>
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#include <netinet6/ip6_var.h>
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#ifndef INT32_MAX
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#define INT32_MAX 0x7fffffffU
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#endif
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struct randomtab {
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const int ru_bits; /* resulting bits */
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const long ru_out; /* Time after wich will be reseeded */
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const u_int32_t ru_max; /* Uniq cycle, avoid blackjack prediction */
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const u_int32_t ru_gen; /* Starting generator */
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const u_int32_t ru_n; /* ru_n: prime, ru_n - 1: product of pfacts[] */
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const u_int32_t ru_agen; /* determine ru_a as ru_agen^(2*rand) */
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const u_int32_t ru_m; /* ru_m = 2^x*3^y */
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const u_int32_t pfacts[4]; /* factors of ru_n */
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u_int32_t ru_counter;
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u_int32_t ru_msb;
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u_int32_t ru_x;
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u_int32_t ru_seed, ru_seed2;
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u_int32_t ru_a, ru_b;
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u_int32_t ru_g;
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long ru_reseed;
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};
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static struct randomtab randomtab_32 = {
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32, /* resulting bits */
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180, /* Time after wich will be reseeded */
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1000000000, /* Uniq cycle, avoid blackjack prediction */
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2, /* Starting generator */
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2147483629, /* RU_N-1 = 2^2*3^2*59652323 */
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7, /* determine ru_a as RU_AGEN^(2*rand) */
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1836660096, /* RU_M = 2^7*3^15 - don't change */
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{ 2, 3, 59652323, 0 }, /* factors of ru_n */
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};
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static struct randomtab randomtab_20 = {
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20, /* resulting bits */
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180, /* Time after wich will be reseeded */
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200000, /* Uniq cycle, avoid blackjack prediction */
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2, /* Starting generator */
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524269, /* RU_N-1 = 2^2*3^2*14563 */
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7, /* determine ru_a as RU_AGEN^(2*rand) */
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279936, /* RU_M = 2^7*3^7 - don't change */
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{ 2, 3, 14563, 0 }, /* factors of ru_n */
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};
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static u_int32_t pmod(u_int32_t, u_int32_t, u_int32_t);
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static void initid(struct randomtab *);
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static u_int32_t randomid(struct randomtab *);
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/*
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* Do a fast modular exponation, returned value will be in the range
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* of 0 - (mod-1)
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*/
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static u_int32_t
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pmod(u_int32_t gen, u_int32_t expo, u_int32_t mod)
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{
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u_int64_t s, t, u;
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s = 1;
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t = gen;
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u = expo;
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while (u) {
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if (u & 1)
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s = (s * t) % mod;
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u >>= 1;
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t = (t * t) % mod;
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}
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return (s);
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}
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/*
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* Initalizes the seed and chooses a suitable generator. Also toggles
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* the msb flag. The msb flag is used to generate two distinct
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* cycles of random numbers and thus avoiding reuse of ids.
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*
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* This function is called from id_randomid() when needed, an
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* application does not have to worry about it.
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*/
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static void
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initid(struct randomtab *p)
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{
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u_int32_t j, i;
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int noprime = 1;
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p->ru_x = arc4random() % p->ru_m;
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/* (bits - 1) bits of random seed */
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p->ru_seed = arc4random() & (~0U >> (32 - p->ru_bits + 1));
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p->ru_seed2 = arc4random() & (~0U >> (32 - p->ru_bits + 1));
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/* Determine the LCG we use */
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p->ru_b = (arc4random() & (~0U >> (32 - p->ru_bits))) | 1;
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p->ru_a = pmod(p->ru_agen,
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(arc4random() & (~0U >> (32 - p->ru_bits))) & (~1U), p->ru_m);
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while (p->ru_b % 3 == 0)
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p->ru_b += 2;
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j = arc4random() % p->ru_n;
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/*
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* Do a fast gcd(j, RU_N - 1), so we can find a j with
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* gcd(j, RU_N - 1) == 1, giving a new generator for
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* RU_GEN^j mod RU_N
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*/
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while (noprime) {
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for (i = 0; p->pfacts[i] > 0; i++)
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if (j % p->pfacts[i] == 0)
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break;
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if (p->pfacts[i] == 0)
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noprime = 0;
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else
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j = (j + 1) % p->ru_n;
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}
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p->ru_g = pmod(p->ru_gen, j, p->ru_n);
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p->ru_counter = 0;
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p->ru_reseed = time_second + p->ru_out;
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p->ru_msb = p->ru_msb ? 0 : (1U << (p->ru_bits - 1));
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}
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static u_int32_t
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randomid(struct randomtab *p)
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{
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int i, n;
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u_int32_t tmp;
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if (p->ru_counter >= p->ru_max || time_second > p->ru_reseed)
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initid(p);
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tmp = arc4random();
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/* Skip a random number of ids */
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n = tmp & 0x3; tmp = tmp >> 2;
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if (p->ru_counter + n >= p->ru_max)
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initid(p);
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for (i = 0; i <= n; i++) {
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/* Linear Congruential Generator */
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p->ru_x = (u_int32_t)((u_int64_t)p->ru_a * p->ru_x + p->ru_b) % p->ru_m;
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}
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p->ru_counter += i;
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return (p->ru_seed ^ pmod(p->ru_g, p->ru_seed2 ^ p->ru_x, p->ru_n)) |
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p->ru_msb;
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}
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u_int32_t
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ip6_randomid(void)
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{
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return randomid(&randomtab_32);
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}
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u_int32_t
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ip6_randomflowlabel(void)
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{
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return randomid(&randomtab_20) & 0xfffff;
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}
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