198 lines
5.2 KiB
C
198 lines
5.2 KiB
C
/* $NetBSD: ip_id.c,v 1.8 2004/03/23 05:31:54 itojun Exp $ */
|
|
/* $OpenBSD: ip_id.c,v 1.6 2002/03/15 18:19:52 millert Exp $ */
|
|
|
|
/*
|
|
* 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 15bit
|
|
* 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 = 31104 and a maximal period of m-1.
|
|
*
|
|
* The transaction id is determined by:
|
|
* id[n] = seed xor (g^X[n] mod n)
|
|
*
|
|
* Effectively the id is restricted to the lower 15 bits, thus
|
|
* yielding two different cycles by toggling the msb on and off.
|
|
* This avoids reuse issues caused by reseeding.
|
|
*/
|
|
|
|
#include <sys/cdefs.h>
|
|
__KERNEL_RCSID(0, "$NetBSD: ip_id.c,v 1.8 2004/03/23 05:31:54 itojun Exp $");
|
|
|
|
#include "opt_inet.h"
|
|
|
|
#include <sys/types.h>
|
|
#include <sys/param.h>
|
|
#include <sys/kernel.h>
|
|
#include <lib/libkern/libkern.h>
|
|
|
|
#include <net/if.h>
|
|
#include <netinet/in.h>
|
|
#include <netinet/ip_var.h>
|
|
|
|
#define RU_OUT 180 /* Time after wich will be reseeded */
|
|
#define RU_MAX 30000 /* Uniq cycle, avoid blackjack prediction */
|
|
#define RU_GEN 2 /* Starting generator */
|
|
#define RU_N 32749 /* RU_N-1 = 2*2*3*2729 */
|
|
#define RU_AGEN 7 /* determine ru_a as RU_AGEN^(2*rand) */
|
|
#define RU_M 31104 /* RU_M = 2^7*3^5 - don't change */
|
|
|
|
#define PFAC_N 3
|
|
const static u_int16_t pfacts[PFAC_N] = {
|
|
2,
|
|
3,
|
|
2729
|
|
};
|
|
|
|
static u_int16_t ru_x;
|
|
static u_int16_t ru_seed, ru_seed2;
|
|
static u_int16_t ru_a, ru_b;
|
|
static u_int16_t ru_g;
|
|
static u_int16_t ru_counter = 0;
|
|
static u_int16_t ru_msb = 0;
|
|
static long ru_reseed;
|
|
static u_int32_t tmp; /* Storage for unused random */
|
|
|
|
static u_int16_t pmod(u_int16_t, u_int16_t, u_int16_t);
|
|
static void ip_initid(void);
|
|
|
|
/*
|
|
* Do a fast modular exponation, returned value will be in the range
|
|
* of 0 - (mod-1)
|
|
*/
|
|
|
|
static u_int16_t
|
|
pmod(u_int16_t gen, u_int16_t expo, u_int16_t mod)
|
|
{
|
|
u_int16_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);
|
|
}
|
|
|
|
/*
|
|
* Initalizes 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.
|
|
*/
|
|
static void
|
|
ip_initid(void)
|
|
{
|
|
u_int16_t j, i;
|
|
int noprime = 1;
|
|
|
|
ru_x = ((tmp = arc4random()) & 0xFFFF) % RU_M;
|
|
|
|
/* 15 bits of random seed */
|
|
ru_seed = (tmp >> 16) & 0x7FFF;
|
|
ru_seed2 = arc4random() & 0x7FFF;
|
|
|
|
/* Determine the LCG we use */
|
|
ru_b = ((tmp = arc4random()) & 0xfffe) | 1;
|
|
ru_a = pmod(RU_AGEN, (tmp >> 16) & 0xfffe, RU_M);
|
|
while (ru_b % 3 == 0)
|
|
ru_b += 2;
|
|
|
|
j = (tmp = arc4random()) % RU_N;
|
|
tmp = tmp >> 16;
|
|
|
|
/*
|
|
* 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; i < PFAC_N; i++)
|
|
if (j % pfacts[i] == 0)
|
|
break;
|
|
|
|
if (i >= PFAC_N)
|
|
noprime = 0;
|
|
else
|
|
j = (j + 1) % RU_N;
|
|
}
|
|
|
|
ru_g = pmod(RU_GEN, j, RU_N);
|
|
ru_counter = 0;
|
|
|
|
ru_reseed = time.tv_sec + RU_OUT;
|
|
ru_msb = ru_msb == 0x8000 ? 0 : 0x8000;
|
|
}
|
|
|
|
u_int16_t
|
|
ip_randomid(void)
|
|
{
|
|
int i, n;
|
|
|
|
if (ru_counter >= RU_MAX || time.tv_sec > ru_reseed)
|
|
ip_initid();
|
|
|
|
#if 0
|
|
if (!tmp)
|
|
tmp = arc4random();
|
|
|
|
/* Skip a random number of ids */
|
|
n = tmp & 0x3; tmp = tmp >> 2;
|
|
if (ru_counter + n >= RU_MAX)
|
|
ip_initid();
|
|
#else
|
|
n = 0;
|
|
#endif
|
|
|
|
for (i = 0; i <= n; i++)
|
|
/* Linear Congruential Generator */
|
|
ru_x = (ru_a * ru_x + ru_b) % RU_M;
|
|
|
|
ru_counter += i;
|
|
|
|
return (ru_seed ^ pmod(ru_g, ru_seed2 + ru_x, RU_N)) | ru_msb;
|
|
}
|