1 /* $OpenBSD: ip6_id.c,v 1.19 2025/01/01 13:44:22 bluhm Exp $ */
2 /* $NetBSD: ip6_id.c,v 1.7 2003/09/13 21:32:59 itojun Exp $ */
3 /* $KAME: ip6_id.c,v 1.8 2003/09/06 13:41:06 itojun 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/param.h>
85 #include <sys/kernel.h>
86 #include <sys/mbuf.h>
87 #include <sys/socket.h>
88 #include <sys/systm.h>
89
90 #include <netinet/in.h>
91 #include <netinet/ip6.h>
92
93 struct randomtab {
94 const int ru_bits; /* resulting bits */
95 const long ru_out; /* Time after which will be reseeded */
96 const u_int32_t ru_max; /* Uniq cycle, avoid blackjack prediction */
97 const u_int32_t ru_gen; /* Starting generator */
98 const u_int32_t ru_n; /* ru_n: prime, ru_n - 1: product of pfacts[] */
99 const u_int32_t ru_agen; /* determine ru_a as ru_agen^(2*rand) */
100 const u_int32_t ru_m; /* ru_m = 2^x*3^y */
101 const u_int32_t pfacts[4]; /* factors of ru_n */
102
103 u_int32_t ru_counter;
104 u_int32_t ru_msb;
105
106 u_int32_t ru_x;
107 u_int32_t ru_seed, ru_seed2;
108 u_int32_t ru_a, ru_b;
109 u_int32_t ru_g;
110 long ru_reseed;
111 };
112
113 static struct randomtab randomtab_20 = {
114 20, /* resulting bits */
115 180, /* Time after which will be reseeded */
116 200000, /* Uniq cycle, avoid blackjack prediction */
117 2, /* Starting generator */
118 524269, /* RU_N-1 = 2^2*3^2*14563 */
119 7, /* determine ru_a as RU_AGEN^(2*rand) */
120 279936, /* RU_M = 2^7*3^7 - don't change */
121 { 2, 3, 14563, 0 }, /* factors of ru_n */
122 };
123
124 u_int32_t ip6id_pmod(u_int32_t, u_int32_t, u_int32_t);
125 void ip6id_initid(struct randomtab *);
126 u_int32_t ip6id_randomid(struct randomtab *);
127
128 /*
129 * Do a fast modular exponation, returned value will be in the range
130 * of 0 - (mod-1)
131 */
132
133 u_int32_t
ip6id_pmod(u_int32_t gen,u_int32_t expo,u_int32_t mod)134 ip6id_pmod(u_int32_t gen, u_int32_t expo, u_int32_t mod)
135 {
136 u_int64_t s, t, u;
137
138 s = 1;
139 t = gen;
140 u = expo;
141
142 while (u) {
143 if (u & 1)
144 s = (s * t) % mod;
145 u >>= 1;
146 t = (t * t) % mod;
147 }
148 return (s);
149 }
150
151 /*
152 * Initializes the seed and chooses a suitable generator. Also toggles
153 * the msb flag. The msb flag is used to generate two distinct
154 * cycles of random numbers and thus avoiding reuse of ids.
155 *
156 * This function is called from id_randomid() when needed, an
157 * application does not have to worry about it.
158 */
159 void
ip6id_initid(struct randomtab * p)160 ip6id_initid(struct randomtab *p)
161 {
162 u_int32_t j, i;
163 int noprime = 1;
164
165 p->ru_x = arc4random_uniform(p->ru_m);
166
167 /* (bits - 1) bits of random seed */
168 p->ru_seed = arc4random() & (~0U >> (32 - p->ru_bits + 1));
169 p->ru_seed2 = arc4random() & (~0U >> (32 - p->ru_bits + 1));
170
171 /* Determine the LCG we use */
172 p->ru_b = (arc4random() & (~0U >> (32 - p->ru_bits))) | 1;
173 p->ru_a = ip6id_pmod(p->ru_agen,
174 (arc4random() & (~0U >> (32 - p->ru_bits))) & (~1U), p->ru_m);
175 while (p->ru_b % 3 == 0)
176 p->ru_b += 2;
177
178 j = arc4random_uniform(p->ru_n);
179
180 /*
181 * Do a fast gcd(j, RU_N - 1), so we can find a j with
182 * gcd(j, RU_N - 1) == 1, giving a new generator for
183 * RU_GEN^j mod RU_N
184 */
185 while (noprime) {
186 for (i = 0; p->pfacts[i] > 0; i++)
187 if (j % p->pfacts[i] == 0)
188 break;
189
190 if (p->pfacts[i] == 0)
191 noprime = 0;
192 else
193 j = (j + 1) % p->ru_n;
194 }
195
196 p->ru_g = ip6id_pmod(p->ru_gen, j, p->ru_n);
197 p->ru_counter = 0;
198
199 p->ru_reseed = getuptime() + p->ru_out;
200 p->ru_msb = p->ru_msb ? 0 : (1U << (p->ru_bits - 1));
201 }
202
203 u_int32_t
ip6id_randomid(struct randomtab * p)204 ip6id_randomid(struct randomtab *p)
205 {
206 int i, n;
207
208 if (p->ru_counter >= p->ru_max || getuptime() > p->ru_reseed)
209 ip6id_initid(p);
210
211 /* Skip a random number of ids */
212 n = arc4random() & 0x3;
213 if (p->ru_counter + n >= p->ru_max)
214 ip6id_initid(p);
215
216 for (i = 0; i <= n; i++) {
217 /* Linear Congruential Generator */
218 p->ru_x = (u_int32_t)((u_int64_t)p->ru_a * p->ru_x + p->ru_b) % p->ru_m;
219 }
220
221 p->ru_counter += i;
222
223 return (p->ru_seed ^ ip6id_pmod(p->ru_g, p->ru_seed2 + p->ru_x, p->ru_n)) |
224 p->ru_msb;
225 }
226
227 u_int32_t
ip6_randomflowlabel(void)228 ip6_randomflowlabel(void)
229 {
230 return ip6id_randomid(&randomtab_20) & 0xfffff;
231 }
232