[apple/xnu.git] / bsd / netinet / ip_id.c

/* $OpenBSD: ip_id.c,v 1.2 1999/08/26 13:37:01 provos 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.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by Niels Provos.
 * 4. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * 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.
 *
 * $FreeBSD: src/sys/netinet/ip_id.c,v 1.1.2.1 2001/07/19 06:37:26 kris Exp $
 */

/* 
 * 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)
 *
 * Effectivly 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/param.h>
#include <sys/time.h>
#include <sys/kernel.h>
#include <sys/random.h>

#if RANDOM_IP_ID
#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
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 time_t 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);
u_int16_t ip_randomid(void);

extern u_short ip_id;
extern int ip_use_randomid;
/*
 * Do a fast modular exponation, returned value will be in the range
 * of 0 - (mod-1)
 */

#ifdef __STDC__
static u_int16_t
pmod(u_int16_t gen, u_int16_t exp, u_int16_t mod)
#else
static u_int16_t
pmod(gen, exp, mod)
	u_int16_t gen, exp, mod;
#endif
{
	u_int16_t s, t, u;

	s = 1;
	t = gen;
	u = exp;

	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;
	struct timeval timenow;
	
	getmicrotime(&timenow);
	read_random((void *) &tmp, sizeof(tmp));
	ru_x = (tmp & 0xFFFF) % RU_M;

	/* 15 bits of random seed */
	ru_seed = (tmp >> 16) & 0x7FFF;
	read_random((void *) &tmp, sizeof(tmp));
	ru_seed2 = tmp & 0x7FFF;

	read_random((void *) &tmp, sizeof(tmp));

	/* Determine the LCG we use */
	ru_b = (tmp & 0xfffe) | 1;
	ru_a = pmod(RU_AGEN, (tmp >> 16) & 0xfffe, RU_M);
	while (ru_b % 3 == 0)
	  ru_b += 2;
	
	read_random((void *) &tmp, sizeof(tmp));
	j = tmp % 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 = timenow.tv_sec + RU_OUT;
	ru_msb = ru_msb == 0x8000 ? 0 : 0x8000; 
}

u_int16_t
ip_randomid(void)
{
	int i, n;
	struct timeval timenow;

	/* if net.inet.ip.random_id is disabled,
	 * reverts to the incrementing ip_id
	 */

	if (ip_use_randomid == 0)
		return htons(ip_id++);


	getmicrotime(&timenow);
	if (ru_counter >= RU_MAX || timenow.tv_sec > ru_reseed)
		ip_initid();

	if (!tmp)
		read_random((void *) &tmp, sizeof(tmp));

	/* Skip a random number of ids */
	n = tmp & 0x3; tmp = tmp >> 2;
	if (ru_counter + n >= RU_MAX)
		ip_initid();

	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;
}

#endif /* RANDOM_IP_ID */
Commit	Line	Data
9bccf70c A	1	/* $OpenBSD: ip_id.c,v 1.2 1999/08/26 13:37:01 provos Exp $ */
	2
	3	/*
	4	* Copyright 1998 Niels Provos <provos@citi.umich.edu>
	5	* All rights reserved.
	6	*
	7	* Theo de Raadt <deraadt@openbsd.org> came up with the idea of using
	8	* such a mathematical system to generate more random (yet non-repeating)
	9	* ids to solve the resolver/named problem. But Niels designed the
	10	* actual system based on the constraints.
	11	*
	12	* Redistribution and use in source and binary forms, with or without
	13	* modification, are permitted provided that the following conditions
	14	* are met:
	15	* 1. Redistributions of source code must retain the above copyright
	16	* notice, this list of conditions and the following disclaimer.
	17	* 2. Redistributions in binary form must reproduce the above copyright
	18	* notice, this list of conditions and the following disclaimer in the
	19	* documentation and/or other materials provided with the distribution.
	20	* 3. All advertising materials mentioning features or use of this software
	21	* must display the following acknowledgement:
	22	* This product includes software developed by Niels Provos.
	23	* 4. The name of the author may not be used to endorse or promote products
	24	* derived from this software without specific prior written permission.
	25	*
	26	* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
	27	* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
	28	* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
	29	* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
	30	* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
	31	* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
	32	* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
	33	* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	34	* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
	35	* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	36	*
	37	* $FreeBSD: src/sys/netinet/ip_id.c,v 1.1.2.1 2001/07/19 06:37:26 kris Exp $
	38	*/
	39
	40	/*
	41	* seed = random 15bit
	42	* n = prime, g0 = generator to n,
	43	* j = random so that gcd(j,n-1) == 1
	44	* g = g0^j mod n will be a generator again.
	45	*
	46	* X[0] = random seed.
	47	* X[n] = a*X[n-1]+b mod m is a Linear Congruential Generator
	48	* with a = 7^(even random) mod m,
	49	* b = random with gcd(b,m) == 1
	50	* m = 31104 and a maximal period of m-1.
	51	*
	52	* The transaction id is determined by:
	53	* id[n] = seed xor (g^X[n] mod n)
	54	*
	55	* Effectivly the id is restricted to the lower 15 bits, thus
	56	* yielding two different cycles by toggling the msb on and off.
	57	* This avoids reuse issues caused by reseeding.
	58	*/
	59
9bccf70c A	60	#include <sys/param.h>
	61	#include <sys/time.h>
	62	#include <sys/kernel.h>
	63	#include <sys/random.h>
	64
	65	#if RANDOM_IP_ID
	66	#define RU_OUT 180 /* Time after wich will be reseeded */
	67	#define RU_MAX 30000 /* Uniq cycle, avoid blackjack prediction */
	68	#define RU_GEN 2 /* Starting generator */
	69	#define RU_N 32749 /* RU_N-1 = 2232729 /
	70	#define RU_AGEN 7 /* determine ru_a as RU_AGEN^(2rand) /
	71	#define RU_M 31104 /* RU_M = 2^73^5 - don't change /
	72
	73	#define PFAC_N 3
2d21ac55	74	static u_int16_t pfacts[PFAC_N] = {
9bccf70c A	75	2,
	76	3,
	77	2729
	78	};
	79
	80	static u_int16_t ru_x;
	81	static u_int16_t ru_seed, ru_seed2;
	82	static u_int16_t ru_a, ru_b;
	83	static u_int16_t ru_g;
	84	static u_int16_t ru_counter = 0;
	85	static u_int16_t ru_msb = 0;
b0d623f7	86	static time_t ru_reseed;
9bccf70c A	87	static u_int32_t tmp; /* Storage for unused random */
9bccf70c A	88
91447636 A	89	static u_int16_t pmod(u_int16_t, u_int16_t, u_int16_t);
	90	static void ip_initid(void);
	91	u_int16_t ip_randomid(void);
9bccf70c	92
2d21ac55 A	93	extern u_short ip_id;
2d21ac55 A	94	extern int ip_use_randomid;
9bccf70c A	95	/*
	96	* Do a fast modular exponation, returned value will be in the range
	97	* of 0 - (mod-1)
	98	*/
	99
	100	#ifdef __STDC__
	101	static u_int16_t
	102	pmod(u_int16_t gen, u_int16_t exp, u_int16_t mod)
	103	#else
	104	static u_int16_t
	105	pmod(gen, exp, mod)
	106	u_int16_t gen, exp, mod;
	107	#endif
	108	{
	109	u_int16_t s, t, u;
	110
	111	s = 1;
	112	t = gen;
	113	u = exp;
	114
	115	while (u) {
	116	if (u & 1)
	117	s = (s*t) % mod;
	118	u >>= 1;
	119	t = (t*t) % mod;
	120	}
	121	return (s);
	122	}
	123
	124	/*
	125	* Initalizes the seed and chooses a suitable generator. Also toggles
	126	* the msb flag. The msb flag is used to generate two distinct
	127	* cycles of random numbers and thus avoiding reuse of ids.
	128	*
	129	* This function is called from id_randomid() when needed, an
	130	* application does not have to worry about it.
	131	*/
	132	static void
	133	ip_initid(void)
	134	{
	135	u_int16_t j, i;
	136	int noprime = 1;
2d21ac55 A	137	struct timeval timenow;
	138
	139	getmicrotime(&timenow);
6d2010ae	140	read_random((void *) &tmp, sizeof(tmp));
9bccf70c A	141	ru_x = (tmp & 0xFFFF) % RU_M;
	142
	143	/* 15 bits of random seed */
	144	ru_seed = (tmp >> 16) & 0x7FFF;
	145	read_random((void *) &tmp, sizeof(tmp));
	146	ru_seed2 = tmp & 0x7FFF;
	147
	148	read_random((void *) &tmp, sizeof(tmp));
	149
	150	/* Determine the LCG we use */
	151	ru_b = (tmp & 0xfffe) \| 1;
	152	ru_a = pmod(RU_AGEN, (tmp >> 16) & 0xfffe, RU_M);
	153	while (ru_b % 3 == 0)
	154	ru_b += 2;
	155
	156	read_random((void *) &tmp, sizeof(tmp));
	157	j = tmp % RU_N;
	158	tmp = tmp >> 16;
	159
	160	/*
	161	* Do a fast gcd(j,RU_N-1), so we can find a j with
	162	* gcd(j, RU_N-1) == 1, giving a new generator for
	163	* RU_GEN^j mod RU_N
	164	*/
	165
	166	while (noprime) {
	167	for (i=0; i<PFAC_N; i++)
	168	if (j%pfacts[i] == 0)
	169	break;
	170
	171	if (i>=PFAC_N)
	172	noprime = 0;
	173	else
	174	j = (j+1) % RU_N;
	175	}
	176
	177	ru_g = pmod(RU_GEN,j,RU_N);
	178	ru_counter = 0;
	179
2d21ac55	180	ru_reseed = timenow.tv_sec + RU_OUT;
9bccf70c A	181	ru_msb = ru_msb == 0x8000 ? 0 : 0x8000;
	182	}
	183
	184	u_int16_t
	185	ip_randomid(void)
	186	{
	187	int i, n;
2d21ac55 A	188	struct timeval timenow;
	189
	190	/* if net.inet.ip.random_id is disabled,
	191	* reverts to the incrementing ip_id
	192	*/
	193
	194	if (ip_use_randomid == 0)
	195	return htons(ip_id++);
	196
9bccf70c	197
2d21ac55 A	198	getmicrotime(&timenow);
2d21ac55 A	199	if (ru_counter >= RU_MAX \|\| timenow.tv_sec > ru_reseed)
9bccf70c A	200	ip_initid();
	201
	202	if (!tmp)
	203	read_random((void *) &tmp, sizeof(tmp));
	204
	205	/* Skip a random number of ids */
	206	n = tmp & 0x3; tmp = tmp >> 2;
	207	if (ru_counter + n >= RU_MAX)
	208	ip_initid();
	209
	210	for (i = 0; i <= n; i++)
	211	/* Linear Congruential Generator */
	212	ru_x = (ru_a*ru_x + ru_b) % RU_M;
	213
	214	ru_counter += i;
	215
	216	return (ru_seed ^ pmod(ru_g,ru_seed2 ^ ru_x,RU_N)) \| ru_msb;
	217	}
	218
	219	#endif /* RANDOM_IP_ID */