1 /* $NetBSD: randomid.c,v 1.5 2003/09/13 21:27:43 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 1.5 2003/09/13 21:27:43 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 }; 118 119 struct randomid_ctx { 120 struct randomconf *ru_conf; 121 #define ru_bits ru_conf->rc_bits 122 #define ru_max ru_conf->rc_max 123 #define ru_gen ru_conf->rc_gen 124 #define ru_n ru_conf->rc_n 125 #define ru_agen ru_conf->rc_agen 126 #define ru_m ru_conf->rc_m 127 #define ru_pfacts ru_conf->rc_pfacts 128 long ru_out; /* Time after wich will be reseeded */ 129 u_int32_t ru_counter; 130 u_int32_t ru_msb; 131 132 u_int32_t ru_x; 133 u_int32_t ru_seed, ru_seed2; 134 u_int32_t ru_a, ru_b; 135 u_int32_t ru_g; 136 long ru_reseed; 137 }; 138 139 static struct randomconf randomconf[] = { 140 { 141 32, /* resulting bits */ 142 1000000000, /* Uniq cycle, avoid blackjack prediction */ 143 2, /* Starting generator */ 144 2147483629, /* RU_N-1 = 2^2*3^2*59652323 */ 145 7, /* determine ru_a as RU_AGEN^(2*rand) */ 146 1836660096, /* RU_M = 2^7*3^15 - don't change */ 147 { 2, 3, 59652323, 0 }, /* factors of ru_n */ 148 }, 149 { 150 20, /* resulting bits */ 151 200000, /* Uniq cycle, avoid blackjack prediction */ 152 2, /* Starting generator */ 153 524269, /* RU_N-1 = 2^2*3^2*14563 */ 154 7, /* determine ru_a as RU_AGEN^(2*rand) */ 155 279936, /* RU_M = 2^7*3^7 - don't change */ 156 { 2, 3, 14563, 0 }, /* factors of ru_n */ 157 }, 158 { 159 16, /* resulting bits */ 160 30000, /* Uniq cycle, avoid blackjack prediction */ 161 2, /* Starting generator */ 162 32749, /* RU_N-1 = 2^2*3*2729 */ 163 7, /* determine ru_a as RU_AGEN^(2*rand) */ 164 31104, /* RU_M = 2^7*3^5 - don't change */ 165 { 2, 3, 2729, 0 }, /* factors of ru_n */ 166 }, 167 { 168 -1, /* termination */ 169 }, 170 }; 171 172 static u_int32_t pmod(u_int32_t, u_int32_t, u_int32_t); 173 static void initid(struct randomid_ctx *); 174 175 struct randomid_ctx *randomid_new(int, long); 176 void randomid_delete(struct randomid_ctx *); 177 u_int32_t randomid(struct randomid_ctx *); 178 179 /* 180 * Do a fast modular exponation, returned value will be in the range 181 * of 0 - (mod-1) 182 */ 183 184 static u_int32_t 185 pmod(u_int32_t gen, u_int32_t expo, u_int32_t mod) 186 { 187 u_int64_t s, t, u; 188 189 s = 1; 190 t = gen; 191 u = expo; 192 193 while (u) { 194 if (u & 1) 195 s = (s * t) % mod; 196 u >>= 1; 197 t = (t * t) % mod; 198 } 199 return ((u_int32_t)s & UINT32_MAX); 200 } 201 202 /* 203 * Initalizes the seed and chooses a suitable generator. Also toggles 204 * the msb flag. The msb flag is used to generate two distinct 205 * cycles of random numbers and thus avoiding reuse of ids. 206 * 207 * This function is called from id_randomid() when needed, an 208 * application does not have to worry about it. 209 */ 210 static void 211 initid(struct randomid_ctx *p) 212 { 213 u_int32_t j, i; 214 int noprime = 1; 215 struct timeval tv; 216 217 p->ru_x = arc4random() % p->ru_m; 218 219 /* (bits - 1) bits of random seed */ 220 p->ru_seed = arc4random() & (~0U >> (32 - p->ru_bits + 1)); 221 p->ru_seed2 = arc4random() & (~0U >> (32 - p->ru_bits + 1)); 222 223 /* Determine the LCG we use */ 224 p->ru_b = arc4random() | 1; 225 p->ru_a = pmod(p->ru_agen, arc4random() & (~1U), p->ru_m); 226 while (p->ru_b % 3 == 0) 227 p->ru_b += 2; 228 229 j = arc4random() % p->ru_n; 230 231 /* 232 * Do a fast gcd(j, RU_N - 1), so we can find a j with 233 * gcd(j, RU_N - 1) == 1, giving a new generator for 234 * RU_GEN^j mod RU_N 235 */ 236 while (noprime) { 237 for (i = 0; p->ru_pfacts[i] > 0; i++) 238 if (j % p->ru_pfacts[i] == 0) 239 break; 240 241 if (p->ru_pfacts[i] == 0) 242 noprime = 0; 243 else 244 j = (j + 1) % p->ru_n; 245 } 246 247 p->ru_g = pmod(p->ru_gen, j, p->ru_n); 248 p->ru_counter = 0; 249 250 gettimeofday(&tv, NULL); 251 p->ru_reseed = tv.tv_sec + p->ru_out; 252 p->ru_msb = p->ru_msb ? 0 : (1U << (p->ru_bits - 1)); 253 } 254 255 struct randomid_ctx * 256 randomid_new(int bits, long timeo) 257 { 258 struct randomconf *conf; 259 struct randomid_ctx *ctx; 260 261 if (timeo < RANDOMID_TIMEO_MIN) { 262 errno = EINVAL; 263 return (NULL); 264 } 265 266 for (conf = randomconf; conf->rc_bits > 0; conf++) { 267 if (bits == conf->rc_bits) 268 break; 269 } 270 271 /* unsupported bits */ 272 if (bits != conf->rc_bits) { 273 errno = ENOTSUP; 274 return (NULL); 275 } 276 277 ctx = malloc(sizeof(*ctx)); 278 if (!ctx) 279 return (NULL); 280 281 memset(ctx, 0, sizeof(*ctx)); 282 ctx->ru_conf = conf; 283 ctx->ru_out = timeo; 284 285 return (ctx); 286 } 287 288 void 289 randomid_delete(struct randomid_ctx *ctx) 290 { 291 292 memset(ctx, 0, sizeof(*ctx)); 293 free(ctx); 294 } 295 296 u_int32_t 297 randomid(struct randomid_ctx *p) 298 { 299 int i, n; 300 u_int32_t tmp; 301 struct timeval tv; 302 303 gettimeofday(&tv, NULL); 304 if (p->ru_counter >= p->ru_max || tv.tv_sec > p->ru_reseed) 305 initid(p); 306 307 tmp = arc4random(); 308 309 /* Skip a random number of ids */ 310 n = tmp & 0x3; tmp = tmp >> 2; 311 if (p->ru_counter + n >= p->ru_max) 312 initid(p); 313 314 for (i = 0; i <= n; i++) { 315 /* Linear Congruential Generator */ 316 p->ru_x = (p->ru_a * p->ru_x + p->ru_b) % p->ru_m; 317 } 318 319 p->ru_counter += i; 320 321 return (p->ru_seed ^ pmod(p->ru_g, p->ru_seed2 ^ p->ru_x, p->ru_n)) | 322 p->ru_msb; 323 } 324