1/* $NetBSD: ip6_id.c,v 1.18 2015/08/07 08:11:33 ozaki-r Exp $ */
2/* $KAME: ip6_id.c,v 1.8 2003/09/06 13:41:06 itojun Exp $ */
3/* $OpenBSD: ip_id.c,v 1.6 2002/03/15 18:19:52 millert Exp $ */
4
5/*
6 * Copyright (C) 2003 WIDE Project.
7 * All rights reserved.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 * 1. Redistributions of source code must retain the above copyright
13 * notice, this list of conditions and the following disclaimer.
14 * 2. Redistributions in binary form must reproduce the above copyright
15 * notice, this list of conditions and the following disclaimer in the
16 * documentation and/or other materials provided with the distribution.
17 * 3. Neither the name of the project nor the names of its contributors
18 * may be used to endorse or promote products derived from this software
19 * without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * SUCH DAMAGE.
32 */
33
34/*
35 * Copyright 1998 Niels Provos <provos@citi.umich.edu>
36 * All rights reserved.
37 *
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.
42 *
43 * Redistribution and use in source and binary forms, with or without
44 * modification, are permitted provided that the following conditions
45 * are met:
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.
51 *
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.
62 */
63
64/*
65 * seed = random (bits - 1) bit
66 * n = prime, g0 = generator to n,
67 * j = random so that gcd(j,n-1) == 1
68 * g = g0^j mod n will be a generator again.
69 *
70 * X[0] = random seed.
71 * X[n] = a*X[n-1]+b mod m is a Linear Congruential Generator
72 * with a = 7^(even random) mod m,
73 * b = random with gcd(b,m) == 1
74 * m = constant and a maximal period of m-1.
75 *
76 * The transaction id is determined by:
77 * id[n] = seed xor (g^X[n] mod n)
78 *
79 * Effectively the id is restricted to the lower (bits - 1) bits, thus
80 * yielding two different cycles by toggling the msb on and off.
81 * This avoids reuse issues caused by reseeding.
82 */
83
84#include <sys/cdefs.h>
85__KERNEL_RCSID(0, "$NetBSD: ip6_id.c,v 1.18 2015/08/07 08:11:33 ozaki-r Exp $");
86
87#include <sys/param.h>
88#include <sys/cprng.h>
89
90#include <lib/libkern/libkern.h>
91
92#include <net/if.h>
93#include <netinet/in.h>
94#include <netinet/ip6.h>
95#include <netinet6/ip6_var.h>
96
97struct randomtab {
98 const int ru_bits; /* resulting bits */
99 const long ru_out; /* Time after wich will be reseeded */
100 const u_int32_t ru_max; /* Uniq cycle, avoid blackjack prediction */
101 const u_int32_t ru_gen; /* Starting generator */
102 const u_int32_t ru_n; /* ru_n: prime, ru_n - 1: product of pfacts[] */
103 const u_int32_t ru_agen; /* determine ru_a as ru_agen^(2*rand) */
104 const u_int32_t ru_m; /* ru_m = 2^x*3^y */
105 const u_int32_t ru_pfacts[4]; /* factors of ru_n */
106
107 u_int32_t ru_counter;
108 u_int32_t ru_msb;
109
110 u_int32_t ru_x;
111 u_int32_t ru_seed, ru_seed2;
112 u_int32_t ru_a, ru_b;
113 u_int32_t ru_g;
114 long ru_reseed;
115};
116
117static struct randomtab randomtab_32 = {
118 .ru_bits = 32, /* resulting bits */
119 .ru_out = 180, /* Time after wich will be reseeded */
120 .ru_max = 1000000000, /* Uniq cycle, avoid blackjack prediction */
121 .ru_gen = 2, /* Starting generator */
122 .ru_n = 2147483629, /* RU_N-1 = 2^2*3^2*59652323 */
123 .ru_agen = 7, /* determine ru_a as RU_AGEN^(2*rand) */
124 .ru_m = 1836660096, /* RU_M = 2^7*3^15 - don't change */
125 .ru_pfacts = { 2, 3, 59652323, 0 }, /* factors of ru_n */
126};
127
128static struct randomtab randomtab_20 = {
129 .ru_bits = 20, /* resulting bits */
130 .ru_out = 180, /* Time after wich will be reseeded */
131 .ru_max = 200000, /* Uniq cycle, avoid blackjack prediction */
132 .ru_gen = 2, /* Starting generator */
133 .ru_n = 524269, /* RU_N-1 = 2^2*3^2*14563 */
134 .ru_agen = 7, /* determine ru_a as RU_AGEN^(2*rand) */
135 .ru_m = 279936, /* RU_M = 2^7*3^7 - don't change */
136 .ru_pfacts = { 2, 3, 14563, 0 }, /* factors of ru_n */
137};
138
139static u_int32_t pmod(u_int32_t, u_int32_t, u_int32_t);
140static void initid(struct randomtab *);
141static u_int32_t randomid(struct randomtab *);
142
143/*
144 * Do a fast modular exponation, returned value will be in the range
145 * of 0 - (mod-1)
146 */
147
148static u_int32_t
149pmod(u_int32_t gen, u_int32_t expo, u_int32_t mod)
150{
151 u_int64_t s, t, u;
152
153 s = 1;
154 t = gen;
155 u = expo;
156
157 while (u) {
158 if (u & 1)
159 s = (s * t) % mod;
160 u >>= 1;
161 t = (t * t) % mod;
162 }
163 return (s);
164}
165
166/*
167 * Initalizes the seed and chooses a suitable generator. Also toggles
168 * the msb flag. The msb flag is used to generate two distinct
169 * cycles of random numbers and thus avoiding reuse of ids.
170 *
171 * This function is called from id_randomid() when needed, an
172 * application does not have to worry about it.
173 */
174static void
175initid(struct randomtab *p)
176{
177 u_int32_t j, i;
178 int noprime = 1;
179
180 p->ru_x = cprng_fast32() % p->ru_m;
181
182 /* (bits - 1) bits of random seed */
183 p->ru_seed = cprng_fast32() & (~0U >> (32 - p->ru_bits + 1));
184 p->ru_seed2 = cprng_fast32() & (~0U >> (32 - p->ru_bits + 1));
185
186 /* Determine the LCG we use */
187 p->ru_b = (cprng_fast32() & (~0U >> (32 - p->ru_bits))) | 1;
188 p->ru_a = pmod(p->ru_agen,
189 (cprng_fast32() & (~0U >> (32 - p->ru_bits))) & (~1U), p->ru_m);
190 while (p->ru_b % 3 == 0)
191 p->ru_b += 2;
192
193 j = cprng_fast32() % p->ru_n;
194
195 /*
196 * Do a fast gcd(j, RU_N - 1), so we can find a j with
197 * gcd(j, RU_N - 1) == 1, giving a new generator for
198 * RU_GEN^j mod RU_N
199 */
200 while (noprime) {
201 for (i = 0; p->ru_pfacts[i] > 0; i++)
202 if (j % p->ru_pfacts[i] == 0)
203 break;
204
205 if (p->ru_pfacts[i] == 0)
206 noprime = 0;
207 else
208 j = (j + 1) % p->ru_n;
209 }
210
211 p->ru_g = pmod(p->ru_gen, j, p->ru_n);
212 p->ru_counter = 0;
213
214 p->ru_reseed = time_uptime + p->ru_out;
215 p->ru_msb = p->ru_msb ? 0 : (1U << (p->ru_bits - 1));
216}
217
218static u_int32_t
219randomid(struct randomtab *p)
220{
221 int i, n;
222
223 if (p->ru_counter >= p->ru_max || time_uptime > p->ru_reseed)
224 initid(p);
225
226 /* Skip a random number of ids */
227 n = cprng_fast32() & 0x3;
228 if (p->ru_counter + n >= p->ru_max)
229 initid(p);
230
231 for (i = 0; i <= n; i++) {
232 /* Linear Congruential Generator */
233 p->ru_x = ((u_int64_t)p->ru_a * p->ru_x + p->ru_b) % p->ru_m;
234 }
235
236 p->ru_counter += i;
237
238 return (p->ru_seed ^ pmod(p->ru_g, p->ru_seed2 + p->ru_x, p->ru_n)) |
239 p->ru_msb;
240}
241
242u_int32_t
243ip6_randomid(void)
244{
245
246 return randomid(&randomtab_32);
247}
248
249u_int32_t
250ip6_randomflowlabel(void)
251{
252
253 return randomid(&randomtab_20) & 0xfffff;
254}
255