randomid.c revision 1.1
1 /* $NetBSD: randomid.c,v 1.1 2003/09/09 22:10:34 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 (at) citi.umich.edu> 36 * All rights reserved. 37 * 38 * Theo de Raadt <deraadt (at) 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 1.1 2003/09/09 22:10:34 itojun Exp $"); 92 #endif 93 94 #include <sys/types.h> 95 #include <sys/time.h> 96 #include <stdlib.h> 97 #include <errno.h> 98 #include <randomid.h> 99 100 struct randomconf { 101 const int rc_bits; /* resulting bits */ 102 const u_int32_t rc_max; /* Uniq cycle, avoid blackjack prediction */ 103 const u_int32_t rc_gen; /* Starting generator */ 104 const u_int32_t rc_n; /* ru_n: prime, ru_n - 1: product of pfacts[] */ 105 const u_int32_t rc_agen; /* determine ru_a as ru_agen^(2*rand) */ 106 const u_int32_t rc_m; /* ru_m = 2^x*3^y */ 107 const u_int32_t rc_pfacts[4]; /* factors of ru_n */ 108 }; 109 110 struct randomid_ctx { 111 struct randomconf *ru_conf; 112 #define ru_bits ru_conf->rc_bits 113 #define ru_max ru_conf->rc_max 114 #define ru_gen ru_conf->rc_gen 115 #define ru_n ru_conf->rc_n 116 #define ru_agen ru_conf->rc_agen 117 #define ru_m ru_conf->rc_m 118 #define ru_pfacts ru_conf->rc_pfacts 119 long ru_out; /* Time after wich will be reseeded */ 120 u_int32_t ru_counter; 121 u_int32_t ru_msb; 122 123 u_int32_t ru_x; 124 u_int32_t ru_seed, ru_seed2; 125 u_int32_t ru_a, ru_b; 126 u_int32_t ru_g; 127 long ru_reseed; 128 }; 129 130 static struct randomconf randomconf[] = { 131 { 132 32, /* resulting bits */ 133 1000000000, /* Uniq cycle, avoid blackjack prediction */ 134 2, /* Starting generator */ 135 2147483629, /* RU_N-1 = 2^2*3^2*59652323 */ 136 7, /* determine ru_a as RU_AGEN^(2*rand) */ 137 1836660096, /* RU_M = 2^7*3^15 - don't change */ 138 { 2, 3, 59652323, 0 }, /* factors of ru_n */ 139 }, 140 { 141 20, /* resulting bits */ 142 200000, /* Uniq cycle, avoid blackjack prediction */ 143 2, /* Starting generator */ 144 524269, /* RU_N-1 = 2^2*3^2*14563 */ 145 7, /* determine ru_a as RU_AGEN^(2*rand) */ 146 279936, /* RU_M = 2^7*3^7 - don't change */ 147 { 2, 3, 14563, 0 }, /* factors of ru_n */ 148 }, 149 { 150 16, /* resulting bits */ 151 30000, /* Uniq cycle, avoid blackjack prediction */ 152 2, /* Starting generator */ 153 32749, /* RU_N-1 = 2^2*3*2729 */ 154 7, /* determine ru_a as RU_AGEN^(2*rand) */ 155 31104, /* RU_M = 2^7*3^5 - don't change */ 156 { 2, 3, 2729, 0 }, /* factors of ru_n */ 157 }, 158 { 159 -1, /* termination */ 160 }, 161 }; 162 163 static u_int32_t pmod(u_int32_t, u_int32_t, u_int32_t); 164 static void initid(struct randomid_ctx *); 165 166 struct randomid_ctx *randomid_new(int, long); 167 void randomid_delete(struct randomid_ctx *); 168 u_int32_t randomid(struct randomid_ctx *); 169 170 /* 171 * Do a fast modular exponation, returned value will be in the range 172 * of 0 - (mod-1) 173 */ 174 175 static u_int32_t 176 pmod(u_int32_t gen, u_int32_t exp, u_int32_t mod) 177 { 178 u_int64_t s, t, u; 179 180 s = 1; 181 t = gen; 182 u = exp; 183 184 while (u) { 185 if (u & 1) 186 s = (s * t) % mod; 187 u >>= 1; 188 t = (t * t) % mod; 189 } 190 return ((u_int32_t)s & UINT32_MAX); 191 } 192 193 /* 194 * Initalizes the seed and chooses a suitable generator. Also toggles 195 * the msb flag. The msb flag is used to generate two distinct 196 * cycles of random numbers and thus avoiding reuse of ids. 197 * 198 * This function is called from id_randomid() when needed, an 199 * application does not have to worry about it. 200 */ 201 static void 202 initid(struct randomid_ctx *p) 203 { 204 u_int32_t j, i; 205 int noprime = 1; 206 struct timeval tv; 207 208 p->ru_x = arc4random() % p->ru_m; 209 210 /* (bits - 1) bits of random seed */ 211 p->ru_seed = arc4random() & (~0U >> (32 - p->ru_bits + 1)); 212 p->ru_seed2 = arc4random() & (~0U >> (32 - p->ru_bits + 1)); 213 214 /* Determine the LCG we use */ 215 p->ru_b = arc4random() | 1; 216 p->ru_a = pmod(p->ru_agen, arc4random() & (~1U), p->ru_m); 217 while (p->ru_b % 3 == 0) 218 p->ru_b += 2; 219 220 j = arc4random() % p->ru_n; 221 222 /* 223 * Do a fast gcd(j, RU_N - 1), so we can find a j with 224 * gcd(j, RU_N - 1) == 1, giving a new generator for 225 * RU_GEN^j mod RU_N 226 */ 227 while (noprime) { 228 for (i = 0; p->ru_pfacts[i] > 0; i++) 229 if (j % p->ru_pfacts[i] == 0) 230 break; 231 232 if (p->ru_pfacts[i] == 0) 233 noprime = 0; 234 else 235 j = (j + 1) % p->ru_n; 236 } 237 238 p->ru_g = pmod(p->ru_gen, j, p->ru_n); 239 p->ru_counter = 0; 240 241 gettimeofday(&tv, NULL); 242 p->ru_reseed = tv.tv_sec + p->ru_out; 243 p->ru_msb = p->ru_msb ? 0 : (1U << (p->ru_bits - 1)); 244 } 245 246 struct randomid_ctx * 247 randomid_new(int bits, long timeo) 248 { 249 struct randomconf *conf; 250 struct randomid_ctx *ctx; 251 252 if (timeo < RANDOMID_TIMEO_MIN) { 253 errno = EINVAL; 254 return (NULL); 255 } 256 257 for (conf = randomconf; conf->rc_bits > 0; conf++) { 258 if (bits == conf->rc_bits) 259 break; 260 } 261 262 /* unsupported bits */ 263 if (bits != conf->rc_bits) { 264 errno = ENOTSUP; 265 return (NULL); 266 } 267 268 ctx = malloc(sizeof(*ctx)); 269 memset(ctx, 0, sizeof(*ctx)); 270 ctx->ru_conf = conf; 271 ctx->ru_out = timeo; 272 273 return (ctx); 274 } 275 276 void 277 randomid_delete(struct randomid_ctx *ctx) 278 { 279 280 memset(ctx, 0, sizeof(*ctx)); 281 free(ctx); 282 } 283 284 u_int32_t 285 randomid(struct randomid_ctx *p) 286 { 287 int i, n; 288 u_int32_t tmp; 289 struct timeval tv; 290 291 gettimeofday(&tv, NULL); 292 if (p->ru_counter >= p->ru_max || tv.tv_sec > p->ru_reseed) 293 initid(p); 294 295 tmp = arc4random(); 296 297 /* Skip a random number of ids */ 298 n = tmp & 0x3; tmp = tmp >> 2; 299 if (p->ru_counter + n >= p->ru_max) 300 initid(p); 301 302 for (i = 0; i <= n; i++) { 303 /* Linear Congruential Generator */ 304 p->ru_x = (p->ru_a * p->ru_x + p->ru_b) % p->ru_m; 305 } 306 307 p->ru_counter += i; 308 309 return (p->ru_seed ^ pmod(p->ru_g, p->ru_seed2 ^ p->ru_x, p->ru_n)) | 310 p->ru_msb; 311 } 312
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