Annotation of sys/netinet6/ip6_id.c, Revision 1.1.1.1
1.1 nbrk 1: /* $OpenBSD: ip6_id.c,v 1.4 2004/06/21 23:50:37 tholo 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: * Effectivly 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/types.h>
85: #include <sys/param.h>
86: #include <sys/kernel.h>
87: #include <sys/socket.h>
88:
89: #include <net/if.h>
90: #include <netinet/in.h>
91: #include <netinet/ip6.h>
92: #include <netinet6/ip6_var.h>
93:
94: #include <dev/rndvar.h>
95:
96: struct randomtab {
97: const int ru_bits; /* resulting bits */
98: const long ru_out; /* Time after wich will be reseeded */
99: const u_int32_t ru_max; /* Uniq cycle, avoid blackjack prediction */
100: const u_int32_t ru_gen; /* Starting generator */
101: const u_int32_t ru_n; /* ru_n: prime, ru_n - 1: product of pfacts[] */
102: const u_int32_t ru_agen; /* determine ru_a as ru_agen^(2*rand) */
103: const u_int32_t ru_m; /* ru_m = 2^x*3^y */
104: const u_int32_t pfacts[4]; /* factors of ru_n */
105:
106: u_int32_t ru_counter;
107: u_int32_t ru_msb;
108:
109: u_int32_t ru_x;
110: u_int32_t ru_seed, ru_seed2;
111: u_int32_t ru_a, ru_b;
112: u_int32_t ru_g;
113: long ru_reseed;
114: };
115:
116: static struct randomtab randomtab_32 = {
117: 32, /* resulting bits */
118: 180, /* Time after wich will be reseeded */
119: 1000000000, /* Uniq cycle, avoid blackjack prediction */
120: 2, /* Starting generator */
121: 2147483629, /* RU_N-1 = 2^2*3^2*59652323 */
122: 7, /* determine ru_a as RU_AGEN^(2*rand) */
123: 1836660096, /* RU_M = 2^7*3^15 - don't change */
124: { 2, 3, 59652323, 0 }, /* factors of ru_n */
125: };
126:
127: static struct randomtab randomtab_20 = {
128: 20, /* resulting bits */
129: 180, /* Time after wich will be reseeded */
130: 200000, /* Uniq cycle, avoid blackjack prediction */
131: 2, /* Starting generator */
132: 524269, /* RU_N-1 = 2^2*3^2*14563 */
133: 7, /* determine ru_a as RU_AGEN^(2*rand) */
134: 279936, /* RU_M = 2^7*3^7 - don't change */
135: { 2, 3, 14563, 0 }, /* factors of ru_n */
136: };
137:
138: static u_int32_t pmod(u_int32_t, u_int32_t, u_int32_t);
139: static void initid(struct randomtab *);
140: static u_int32_t randomid(struct randomtab *);
141:
142: /*
143: * Do a fast modular exponation, returned value will be in the range
144: * of 0 - (mod-1)
145: */
146:
147: static u_int32_t
148: pmod(u_int32_t gen, u_int32_t expo, u_int32_t mod)
149: {
150: u_int64_t s, t, u;
151:
152: s = 1;
153: t = gen;
154: u = expo;
155:
156: while (u) {
157: if (u & 1)
158: s = (s * t) % mod;
159: u >>= 1;
160: t = (t * t) % mod;
161: }
162: return (s);
163: }
164:
165: /*
166: * Initalizes the seed and chooses a suitable generator. Also toggles
167: * the msb flag. The msb flag is used to generate two distinct
168: * cycles of random numbers and thus avoiding reuse of ids.
169: *
170: * This function is called from id_randomid() when needed, an
171: * application does not have to worry about it.
172: */
173: static void
174: initid(struct randomtab *p)
175: {
176: u_int32_t j, i;
177: int noprime = 1;
178:
179: p->ru_x = arc4random() % p->ru_m;
180:
181: /* (bits - 1) bits of random seed */
182: p->ru_seed = arc4random() & (~0U >> (32 - p->ru_bits + 1));
183: p->ru_seed2 = arc4random() & (~0U >> (32 - p->ru_bits + 1));
184:
185: /* Determine the LCG we use */
186: p->ru_b = (arc4random() & (~0U >> (32 - p->ru_bits))) | 1;
187: p->ru_a = pmod(p->ru_agen,
188: (arc4random() & (~0U >> (32 - p->ru_bits))) & (~1U), p->ru_m);
189: while (p->ru_b % 3 == 0)
190: p->ru_b += 2;
191:
192: j = arc4random() % p->ru_n;
193:
194: /*
195: * Do a fast gcd(j, RU_N - 1), so we can find a j with
196: * gcd(j, RU_N - 1) == 1, giving a new generator for
197: * RU_GEN^j mod RU_N
198: */
199: while (noprime) {
200: for (i = 0; p->pfacts[i] > 0; i++)
201: if (j % p->pfacts[i] == 0)
202: break;
203:
204: if (p->pfacts[i] == 0)
205: noprime = 0;
206: else
207: j = (j + 1) % p->ru_n;
208: }
209:
210: p->ru_g = pmod(p->ru_gen, j, p->ru_n);
211: p->ru_counter = 0;
212:
213: p->ru_reseed = time_second + p->ru_out;
214: p->ru_msb = p->ru_msb ? 0 : (1U << (p->ru_bits - 1));
215: }
216:
217: static u_int32_t
218: randomid(struct randomtab *p)
219: {
220: int i, n;
221:
222: if (p->ru_counter >= p->ru_max || time_second > p->ru_reseed)
223: initid(p);
224:
225: /* Skip a random number of ids */
226: n = arc4random() & 0x3;
227: if (p->ru_counter + n >= p->ru_max)
228: initid(p);
229:
230: for (i = 0; i <= n; i++) {
231: /* Linear Congruential Generator */
232: p->ru_x = (u_int32_t)((u_int64_t)p->ru_a * p->ru_x + p->ru_b) % p->ru_m;
233: }
234:
235: p->ru_counter += i;
236:
237: return (p->ru_seed ^ pmod(p->ru_g, p->ru_seed2 + p->ru_x, p->ru_n)) |
238: p->ru_msb;
239: }
240:
241: u_int32_t
242: ip6_randomid(void)
243: {
244:
245: return randomid(&randomtab_32);
246: }
247:
248: u_int32_t
249: ip6_randomflowlabel(void)
250: {
251:
252: return randomid(&randomtab_20) & 0xfffff;
253: }
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