1 /* $NetBSD: randomid.c,v 1.10 2003/12/10 05:22:18 itojun 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 * 3. All advertising materials mentioning features or use of this software 52 * must display the following acknowledgement: 53 * This product includes software developed by Niels Provos. 54 * 4. The name of the author may not be used to endorse or promote products 55 * derived from this software without specific prior written permission. 56 * 57 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 58 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 59 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 60 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 61 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 62 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 63 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 64 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 65 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 66 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 67 */ 68 69 /* 70 * seed = random (bits - 1) bit 71 * n = prime, g0 = generator to n, 72 * j = random so that gcd(j,n-1) == 1 73 * g = g0^j mod n will be a generator again. 74 * 75 * X[0] = random seed. 76 * X[n] = a*X[n-1]+b mod m is a Linear Congruential Generator 77 * with a = 7^(even random) mod m, 78 * b = random with gcd(b,m) == 1 79 * m = constant and a maximal period of m-1. 80 * 81 * The transaction id is determined by: 82 * id[n] = seed xor (g^X[n] mod n) 83 * 84 * Effectivly the id is restricted to the lower (bits - 1) bits, thus 85 * yielding two different cycles by toggling the msb on and off. 86 * This avoids reuse issues caused by reseeding. 87 */ 88 89 #include <sys/cdefs.h> 90 #if defined(LIBC_SCCS) && !defined(lint) 91 __RCSID("$NetBSD: randomid.c,v 1.10 2003/12/10 05:22:18 itojun Exp $"); 92 #endif 93 94 #include "namespace.h" 95 96 #include <sys/types.h> 97 #include <sys/time.h> 98 #include <stdlib.h> 99 #include <string.h> 100 #include <errno.h> 101 #include <randomid.h> 102 103 #ifdef __weak_alias 104 __weak_alias(randomid,_randomid) 105 __weak_alias(randomid_new,_randomid_new) 106 __weak_alias(randomid_delete,_randomid_delete) 107 #endif 108 109 struct randomconf { 110 const int rc_bits; /* resulting bits */ 111 const u_int32_t rc_max; /* Uniq cycle, avoid blackjack prediction */ 112 const u_int32_t rc_gen; /* Starting generator */ 113 const u_int32_t rc_n; /* ru_n: prime, ru_n - 1: product of pfacts[] */ 114 const u_int32_t rc_agen; /* determine ru_a as ru_agen^(2*rand) */ 115 const u_int32_t rc_m; /* ru_m = 2^x*3^y */ 116 const u_int32_t rc_pfacts[4]; /* factors of ru_n */ 117 const int rc_skip; /* skip values */ 118 }; 119 120 struct randomid_ctx { 121 struct randomconf *ru_conf; 122 #define ru_bits ru_conf->rc_bits 123 #define ru_max ru_conf->rc_max 124 #define ru_gen ru_conf->rc_gen 125 #define ru_n ru_conf->rc_n 126 #define ru_agen ru_conf->rc_agen 127 #define ru_m ru_conf->rc_m 128 #define ru_pfacts ru_conf->rc_pfacts 129 #define ru_skip ru_conf->rc_skip 130 long ru_out; /* Time after wich will be reseeded */ 131 u_int32_t ru_counter; 132 u_int32_t ru_msb; 133 134 u_int32_t ru_x; 135 u_int32_t ru_seed, ru_seed2; 136 u_int32_t ru_a, ru_b; 137 u_int32_t ru_g; 138 long ru_reseed; 139 }; 140 141 static struct randomconf randomconf[] = { 142 { 143 32, /* resulting bits */ 144 1000000000, /* Uniq cycle, avoid blackjack prediction */ 145 2, /* Starting generator */ 146 2147483629, /* RU_N-1 = 2^2*3^2*59652323 */ 147 7, /* determine ru_a as RU_AGEN^(2*rand) */ 148 1836660096, /* RU_M = 2^7*3^15 - don't change */ 149 { 2, 3, 59652323, 0 }, /* factors of ru_n */ 150 3, /* skip values */ 151 }, 152 { 153 20, /* resulting bits */ 154 200000, /* Uniq cycle, avoid blackjack prediction */ 155 2, /* Starting generator */ 156 524269, /* RU_N-1 = 2^2*3^2*14563 */ 157 7, /* determine ru_a as RU_AGEN^(2*rand) */ 158 279936, /* RU_M = 2^7*3^7 - don't change */ 159 { 2, 3, 14563, 0 }, /* factors of ru_n */ 160 3, /* skip values */ 161 }, 162 { 163 16, /* resulting bits */ 164 30000, /* Uniq cycle, avoid blackjack prediction */ 165 2, /* Starting generator */ 166 32749, /* RU_N-1 = 2^2*3*2729 */ 167 7, /* determine ru_a as RU_AGEN^(2*rand) */ 168 31104, /* RU_M = 2^7*3^5 - don't change */ 169 { 2, 3, 2729, 0 }, /* factors of ru_n */ 170 0, /* skip values */ 171 }, 172 { 173 -1, /* termination */ 174 }, 175 }; 176 177 static u_int32_t pmod(u_int32_t, u_int32_t, u_int32_t); 178 static void initid(struct randomid_ctx *); 179 180 struct randomid_ctx *randomid_new(int, long); 181 void randomid_delete(struct randomid_ctx *); 182 u_int32_t randomid(struct randomid_ctx *); 183 184 /* 185 * Do a fast modular exponation, returned value will be in the range 186 * of 0 - (mod-1) 187 */ 188 189 static u_int32_t 190 pmod(u_int32_t gen, u_int32_t expo, u_int32_t mod) 191 { 192 u_int64_t s, t, u; 193 194 s = 1; 195 t = gen; 196 u = expo; 197 198 while (u) { 199 if (u & 1) 200 s = (s * t) % mod; 201 u >>= 1; 202 t = (t * t) % mod; 203 } 204 return ((u_int32_t)s & UINT32_MAX); 205 } 206 207 /* 208 * Initalizes the seed and chooses a suitable generator. Also toggles 209 * the msb flag. The msb flag is used to generate two distinct 210 * cycles of random numbers and thus avoiding reuse of ids. 211 * 212 * This function is called from id_randomid() when needed, an 213 * application does not have to worry about it. 214 */ 215 static void 216 initid(struct randomid_ctx *p) 217 { 218 u_int32_t j, i; 219 int noprime = 1; 220 struct timeval tv; 221 222 p->ru_x = arc4random() % p->ru_m; 223 224 /* (bits - 1) bits of random seed */ 225 p->ru_seed = arc4random() & (~0U >> (32 - p->ru_bits + 1)); 226 p->ru_seed2 = arc4random() & (~0U >> (32 - p->ru_bits + 1)); 227 228 /* Determine the LCG we use */ 229 p->ru_b = (arc4random() & (~0U >> (32 - p->ru_bits))) | 1; 230 p->ru_a = pmod(p->ru_agen, 231 (arc4random() & (~0U >> (32 - p->ru_bits))) & (~1U), p->ru_m); 232 while (p->ru_b % 3 == 0) 233 p->ru_b += 2; 234 235 j = arc4random() % p->ru_n; 236 237 /* 238 * Do a fast gcd(j, RU_N - 1), so we can find a j with 239 * gcd(j, RU_N - 1) == 1, giving a new generator for 240 * RU_GEN^j mod RU_N 241 */ 242 while (noprime) { 243 for (i = 0; p->ru_pfacts[i] > 0; i++) 244 if (j % p->ru_pfacts[i] == 0) 245 break; 246 247 if (p->ru_pfacts[i] == 0) 248 noprime = 0; 249 else 250 j = (j + 1) % p->ru_n; 251 } 252 253 p->ru_g = pmod(p->ru_gen, j, p->ru_n); 254 p->ru_counter = 0; 255 256 gettimeofday(&tv, NULL); 257 p->ru_reseed = tv.tv_sec + p->ru_out; 258 p->ru_msb = p->ru_msb ? 0 : (1U << (p->ru_bits - 1)); 259 } 260 261 struct randomid_ctx * 262 randomid_new(int bits, long timeo) 263 { 264 struct randomconf *conf; 265 struct randomid_ctx *ctx; 266 267 if (timeo < RANDOMID_TIMEO_MIN) { 268 errno = EINVAL; 269 return (NULL); 270 } 271 272 for (conf = randomconf; conf->rc_bits > 0; conf++) { 273 if (bits == conf->rc_bits) 274 break; 275 } 276 277 /* unsupported bits */ 278 if (bits != conf->rc_bits) { 279 errno = ENOTSUP; 280 return (NULL); 281 } 282 283 ctx = malloc(sizeof(*ctx)); 284 if (!ctx) 285 return (NULL); 286 287 memset(ctx, 0, sizeof(*ctx)); 288 ctx->ru_conf = conf; 289 ctx->ru_out = timeo; 290 291 return (ctx); 292 } 293 294 void 295 randomid_delete(struct randomid_ctx *ctx) 296 { 297 298 memset(ctx, 0, sizeof(*ctx)); 299 free(ctx); 300 } 301 302 u_int32_t 303 randomid(struct randomid_ctx *p) 304 { 305 int i, n; 306 struct timeval tv; 307 308 gettimeofday(&tv, NULL); 309 if (p->ru_counter >= p->ru_max || tv.tv_sec > p->ru_reseed) 310 initid(p); 311 312 /* Skip a random number of ids */ 313 if (p->ru_skip) { 314 n = arc4random() & p->ru_skip; 315 if (p->ru_counter + n >= p->ru_max) 316 initid(p); 317 } else 318 n = 0; 319 320 for (i = 0; i <= n; i++) { 321 /* Linear Congruential Generator */ 322 p->ru_x = (u_int32_t)(((u_int64_t)p->ru_a * p->ru_x + p->ru_b) % p->ru_m); 323 } 324 325 p->ru_counter += i; 326 327 return (p->ru_seed ^ pmod(p->ru_g, p->ru_seed2 + p->ru_x, p->ru_n)) | 328 p->ru_msb; 329 } 330