2 * SPDX-License-Identifier: (BSD-3-Clause AND BSD-2-Clause)
4 * Copyright (C) 2003 WIDE Project.
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 * 3. Neither the name of the project nor the names of its contributors
16 * may be used to endorse or promote products derived from this software
17 * without specific prior written permission.
19 * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22 * ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * $KAME: ip6_id.c,v 1.13 2003/09/16 09:11:19 itojun Exp $
35 * Copyright 1998 Niels Provos <provos@citi.umich.edu>
36 * All rights reserved.
38 * Theo de Raadt <deraadt@openbsd.org> came up with the idea of using
39 * such a mathematical system to generate more random (yet non-repeating)
40 * ids to solve the resolver/named problem. But Niels designed the
41 * actual system based on the constraints.
43 * Redistribution and use in source and binary forms, with or without
44 * modification, are permitted provided that the following conditions
46 * 1. Redistributions of source code must retain the above copyright
47 * notice, this list of conditions and the following disclaimer.
48 * 2. Redistributions in binary form must reproduce the above copyright
49 * notice, this list of conditions and the following disclaimer in the
50 * documentation and/or other materials provided with the distribution.
52 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
53 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
54 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
55 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
56 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
57 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
58 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
59 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
60 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
61 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
63 * $OpenBSD: ip6_id.c,v 1.3 2003/12/12 06:57:12 itojun Exp $
66 #include <sys/cdefs.h>
67 __FBSDID("$FreeBSD$");
70 * seed = random (bits - 1) bit
71 * n = prime, g0 = generator to n,
72 * j = random so that gcd(j,n-1) == 1
73 * g = g0^j mod n will be a generator again.
76 * X[n] = a*X[n-1]+b mod m is a Linear Congruential Generator
77 * with a = 7^(even random) mod m,
78 * b = random with gcd(b,m) == 1
79 * m = constant and a maximal period of m-1.
81 * The transaction id is determined by:
82 * id[n] = seed xor (g^X[n] mod n)
84 * Effectively the id is restricted to the lower (bits - 1) bits, thus
85 * yielding two different cycles by toggling the msb on and off.
86 * This avoids reuse issues caused by reseeding.
89 #include <sys/types.h>
90 #include <sys/param.h>
91 #include <sys/kernel.h>
92 #include <sys/random.h>
93 #include <sys/socket.h>
94 #include <sys/libkern.h>
97 #include <net/route.h>
99 #include <netinet/in.h>
100 #include <netinet/ip6.h>
101 #include <netinet6/ip6_var.h>
104 #define INT32_MAX 0x7fffffffU
108 const int ru_bits; /* resulting bits */
109 const long ru_out; /* Time after which will be reseeded */
110 const u_int32_t ru_max; /* Uniq cycle, avoid blackjack prediction */
111 const u_int32_t ru_gen; /* Starting generator */
112 const u_int32_t ru_n; /* ru_n: prime, ru_n - 1: product of pfacts[] */
113 const u_int32_t ru_agen; /* determine ru_a as ru_agen^(2*rand) */
114 const u_int32_t ru_m; /* ru_m = 2^x*3^y */
115 const u_int32_t pfacts[4]; /* factors of ru_n */
117 u_int32_t ru_counter;
121 u_int32_t ru_seed, ru_seed2;
122 u_int32_t ru_a, ru_b;
127 static struct randomtab randomtab_32 = {
128 32, /* resulting bits */
129 180, /* Time after which will be reseeded */
130 1000000000, /* Uniq cycle, avoid blackjack prediction */
131 2, /* Starting generator */
132 2147483629, /* RU_N-1 = 2^2*3^2*59652323 */
133 7, /* determine ru_a as RU_AGEN^(2*rand) */
134 1836660096, /* RU_M = 2^7*3^15 - don't change */
135 { 2, 3, 59652323, 0 }, /* factors of ru_n */
138 static struct randomtab randomtab_20 = {
139 20, /* resulting bits */
140 180, /* Time after which will be reseeded */
141 200000, /* Uniq cycle, avoid blackjack prediction */
142 2, /* Starting generator */
143 524269, /* RU_N-1 = 2^2*3^2*14563 */
144 7, /* determine ru_a as RU_AGEN^(2*rand) */
145 279936, /* RU_M = 2^7*3^7 - don't change */
146 { 2, 3, 14563, 0 }, /* factors of ru_n */
149 static u_int32_t pmod(u_int32_t, u_int32_t, u_int32_t);
150 static void initid(struct randomtab *);
151 static u_int32_t randomid(struct randomtab *);
154 * Do a fast modular exponation, returned value will be in the range
158 pmod(u_int32_t gen, u_int32_t expo, u_int32_t mod)
176 * Initializes the seed and chooses a suitable generator. Also toggles
177 * the msb flag. The msb flag is used to generate two distinct
178 * cycles of random numbers and thus avoiding reuse of ids.
180 * This function is called from id_randomid() when needed, an
181 * application does not have to worry about it.
184 initid(struct randomtab *p)
189 p->ru_x = arc4random() % p->ru_m;
191 /* (bits - 1) bits of random seed */
192 p->ru_seed = arc4random() & (~0U >> (32 - p->ru_bits + 1));
193 p->ru_seed2 = arc4random() & (~0U >> (32 - p->ru_bits + 1));
195 /* Determine the LCG we use */
196 p->ru_b = (arc4random() & (~0U >> (32 - p->ru_bits))) | 1;
197 p->ru_a = pmod(p->ru_agen,
198 (arc4random() & (~0U >> (32 - p->ru_bits))) & (~1U), p->ru_m);
199 while (p->ru_b % 3 == 0)
202 j = arc4random() % p->ru_n;
205 * Do a fast gcd(j, RU_N - 1), so we can find a j with
206 * gcd(j, RU_N - 1) == 1, giving a new generator for
210 for (i = 0; p->pfacts[i] > 0; i++)
211 if (j % p->pfacts[i] == 0)
214 if (p->pfacts[i] == 0)
217 j = (j + 1) % p->ru_n;
220 p->ru_g = pmod(p->ru_gen, j, p->ru_n);
223 p->ru_reseed = time_uptime + p->ru_out;
224 p->ru_msb = p->ru_msb ? 0 : (1U << (p->ru_bits - 1));
228 randomid(struct randomtab *p)
232 if (p->ru_counter >= p->ru_max || time_uptime > p->ru_reseed)
235 /* Skip a random number of ids */
236 n = arc4random() & 0x3;
237 if (p->ru_counter + n >= p->ru_max)
240 for (i = 0; i <= n; i++) {
241 /* Linear Congruential Generator */
242 p->ru_x = (u_int32_t)((u_int64_t)p->ru_a * p->ru_x + p->ru_b) % p->ru_m;
247 return (p->ru_seed ^ pmod(p->ru_g, p->ru_seed2 + p->ru_x, p->ru_n)) |
255 return randomid(&randomtab_32);
259 ip6_randomflowlabel(void)
263 * It's ok to emit zero flow labels early, before random is available
264 * (seeded). RFC 6437:
266 * "A Flow Label of zero is used to indicate packets that have not been
269 if (__predict_false(!is_random_seeded()))
272 return randomid(&randomtab_20) & 0xfffff;