1 /* $OpenBSD: ip6_id.c,v 1.7 2008/06/09 22:47:42 djm 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_20 = { 117 20, /* resulting bits */ 118 180, /* Time after wich will be reseeded */ 119 200000, /* Uniq cycle, avoid blackjack prediction */ 120 2, /* Starting generator */ 121 524269, /* RU_N-1 = 2^2*3^2*14563 */ 122 7, /* determine ru_a as RU_AGEN^(2*rand) */ 123 279936, /* RU_M = 2^7*3^7 - don't change */ 124 { 2, 3, 14563, 0 }, /* factors of ru_n */ 125 }; 126 127 static u_int32_t pmod(u_int32_t, u_int32_t, u_int32_t); 128 static void initid(struct randomtab *); 129 static u_int32_t randomid(struct randomtab *); 130 131 /* 132 * Do a fast modular exponation, returned value will be in the range 133 * of 0 - (mod-1) 134 */ 135 136 static u_int32_t 137 pmod(u_int32_t gen, u_int32_t expo, u_int32_t mod) 138 { 139 u_int64_t s, t, u; 140 141 s = 1; 142 t = gen; 143 u = expo; 144 145 while (u) { 146 if (u & 1) 147 s = (s * t) % mod; 148 u >>= 1; 149 t = (t * t) % mod; 150 } 151 return (s); 152 } 153 154 /* 155 * Initializes the seed and chooses a suitable generator. Also toggles 156 * the msb flag. The msb flag is used to generate two distinct 157 * cycles of random numbers and thus avoiding reuse of ids. 158 * 159 * This function is called from id_randomid() when needed, an 160 * application does not have to worry about it. 161 */ 162 static void 163 initid(struct randomtab *p) 164 { 165 u_int32_t j, i; 166 int noprime = 1; 167 168 p->ru_x = arc4random_uniform(p->ru_m); 169 170 /* (bits - 1) bits of random seed */ 171 p->ru_seed = arc4random() & (~0U >> (32 - p->ru_bits + 1)); 172 p->ru_seed2 = arc4random() & (~0U >> (32 - p->ru_bits + 1)); 173 174 /* Determine the LCG we use */ 175 p->ru_b = (arc4random() & (~0U >> (32 - p->ru_bits))) | 1; 176 p->ru_a = pmod(p->ru_agen, 177 (arc4random() & (~0U >> (32 - p->ru_bits))) & (~1U), p->ru_m); 178 while (p->ru_b % 3 == 0) 179 p->ru_b += 2; 180 181 j = arc4random_uniform(p->ru_n); 182 183 /* 184 * Do a fast gcd(j, RU_N - 1), so we can find a j with 185 * gcd(j, RU_N - 1) == 1, giving a new generator for 186 * RU_GEN^j mod RU_N 187 */ 188 while (noprime) { 189 for (i = 0; p->pfacts[i] > 0; i++) 190 if (j % p->pfacts[i] == 0) 191 break; 192 193 if (p->pfacts[i] == 0) 194 noprime = 0; 195 else 196 j = (j + 1) % p->ru_n; 197 } 198 199 p->ru_g = pmod(p->ru_gen, j, p->ru_n); 200 p->ru_counter = 0; 201 202 p->ru_reseed = time_second + p->ru_out; 203 p->ru_msb = p->ru_msb ? 0 : (1U << (p->ru_bits - 1)); 204 } 205 206 static u_int32_t 207 randomid(struct randomtab *p) 208 { 209 int i, n; 210 211 if (p->ru_counter >= p->ru_max || time_second > p->ru_reseed) 212 initid(p); 213 214 /* Skip a random number of ids */ 215 n = arc4random() & 0x3; 216 if (p->ru_counter + n >= p->ru_max) 217 initid(p); 218 219 for (i = 0; i <= n; i++) { 220 /* Linear Congruential Generator */ 221 p->ru_x = (u_int32_t)((u_int64_t)p->ru_a * p->ru_x + p->ru_b) % p->ru_m; 222 } 223 224 p->ru_counter += i; 225 226 return (p->ru_seed ^ pmod(p->ru_g, p->ru_seed2 + p->ru_x, p->ru_n)) | 227 p->ru_msb; 228 } 229 230 u_int32_t 231 ip6_randomflowlabel(void) 232 { 233 return randomid(&randomtab_20) & 0xfffff; 234 } 235 236