Annotation of sys/netinet6/ip6_id.c, Revision 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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