randomid.c revision 1.3
1 /* $NetBSD: randomid.c,v 1.3 2003/09/10 07:20:13 tls 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 1.3 2003/09/10 07:20:13 tls Exp $"); 92 #endif 93 94 #include <sys/types.h> 95 #include <sys/time.h> 96 #include <stdlib.h> 97 #include <string.h> 98 #include <errno.h> 99 #include <randomid.h> 100 101 struct randomconf { 102 const int rc_bits; /* resulting bits */ 103 const u_int32_t rc_max; /* Uniq cycle, avoid blackjack prediction */ 104 const u_int32_t rc_gen; /* Starting generator */ 105 const u_int32_t rc_n; /* ru_n: prime, ru_n - 1: product of pfacts[] */ 106 const u_int32_t rc_agen; /* determine ru_a as ru_agen^(2*rand) */ 107 const u_int32_t rc_m; /* ru_m = 2^x*3^y */ 108 const u_int32_t rc_pfacts[4]; /* factors of ru_n */ 109 }; 110 111 struct randomid_ctx { 112 struct randomconf *ru_conf; 113 #define ru_bits ru_conf->rc_bits 114 #define ru_max ru_conf->rc_max 115 #define ru_gen ru_conf->rc_gen 116 #define ru_n ru_conf->rc_n 117 #define ru_agen ru_conf->rc_agen 118 #define ru_m ru_conf->rc_m 119 #define ru_pfacts ru_conf->rc_pfacts 120 long ru_out; /* Time after wich will be reseeded */ 121 u_int32_t ru_counter; 122 u_int32_t ru_msb; 123 124 u_int32_t ru_x; 125 u_int32_t ru_seed, ru_seed2; 126 u_int32_t ru_a, ru_b; 127 u_int32_t ru_g; 128 long ru_reseed; 129 }; 130 131 static struct randomconf randomconf[] = { 132 { 133 32, /* resulting bits */ 134 1000000000, /* Uniq cycle, avoid blackjack prediction */ 135 2, /* Starting generator */ 136 2147483629, /* RU_N-1 = 2^2*3^2*59652323 */ 137 7, /* determine ru_a as RU_AGEN^(2*rand) */ 138 1836660096, /* RU_M = 2^7*3^15 - don't change */ 139 { 2, 3, 59652323, 0 }, /* factors of ru_n */ 140 }, 141 { 142 20, /* resulting bits */ 143 200000, /* Uniq cycle, avoid blackjack prediction */ 144 2, /* Starting generator */ 145 524269, /* RU_N-1 = 2^2*3^2*14563 */ 146 7, /* determine ru_a as RU_AGEN^(2*rand) */ 147 279936, /* RU_M = 2^7*3^7 - don't change */ 148 { 2, 3, 14563, 0 }, /* factors of ru_n */ 149 }, 150 { 151 16, /* resulting bits */ 152 30000, /* Uniq cycle, avoid blackjack prediction */ 153 2, /* Starting generator */ 154 32749, /* RU_N-1 = 2^2*3*2729 */ 155 7, /* determine ru_a as RU_AGEN^(2*rand) */ 156 31104, /* RU_M = 2^7*3^5 - don't change */ 157 { 2, 3, 2729, 0 }, /* factors of ru_n */ 158 }, 159 { 160 -1, /* termination */ 161 }, 162 }; 163 164 static u_int32_t pmod(u_int32_t, u_int32_t, u_int32_t); 165 static void initid(struct randomid_ctx *); 166 167 struct randomid_ctx *randomid_new(int, long); 168 void randomid_delete(struct randomid_ctx *); 169 u_int32_t randomid(struct randomid_ctx *); 170 171 /* 172 * Do a fast modular exponation, returned value will be in the range 173 * of 0 - (mod-1) 174 */ 175 176 static u_int32_t 177 pmod(u_int32_t gen, u_int32_t expo, u_int32_t mod) 178 { 179 u_int64_t s, t, u; 180 181 s = 1; 182 t = gen; 183 u = expo; 184 185 while (u) { 186 if (u & 1) 187 s = (s * t) % mod; 188 u >>= 1; 189 t = (t * t) % mod; 190 } 191 return ((u_int32_t)s & UINT32_MAX); 192 } 193 194 /* 195 * Initalizes the seed and chooses a suitable generator. Also toggles 196 * the msb flag. The msb flag is used to generate two distinct 197 * cycles of random numbers and thus avoiding reuse of ids. 198 * 199 * This function is called from id_randomid() when needed, an 200 * application does not have to worry about it. 201 */ 202 static void 203 initid(struct randomid_ctx *p) 204 { 205 u_int32_t j, i; 206 int noprime = 1; 207 struct timeval tv; 208 209 p->ru_x = arc4random() % p->ru_m; 210 211 /* (bits - 1) bits of random seed */ 212 p->ru_seed = arc4random() & (~0U >> (32 - p->ru_bits + 1)); 213 p->ru_seed2 = arc4random() & (~0U >> (32 - p->ru_bits + 1)); 214 215 /* Determine the LCG we use */ 216 p->ru_b = arc4random() | 1; 217 p->ru_a = pmod(p->ru_agen, arc4random() & (~1U), p->ru_m); 218 while (p->ru_b % 3 == 0) 219 p->ru_b += 2; 220 221 j = arc4random() % p->ru_n; 222 223 /* 224 * Do a fast gcd(j, RU_N - 1), so we can find a j with 225 * gcd(j, RU_N - 1) == 1, giving a new generator for 226 * RU_GEN^j mod RU_N 227 */ 228 while (noprime) { 229 for (i = 0; p->ru_pfacts[i] > 0; i++) 230 if (j % p->ru_pfacts[i] == 0) 231 break; 232 233 if (p->ru_pfacts[i] == 0) 234 noprime = 0; 235 else 236 j = (j + 1) % p->ru_n; 237 } 238 239 p->ru_g = pmod(p->ru_gen, j, p->ru_n); 240 p->ru_counter = 0; 241 242 gettimeofday(&tv, NULL); 243 p->ru_reseed = tv.tv_sec + p->ru_out; 244 p->ru_msb = p->ru_msb ? 0 : (1U << (p->ru_bits - 1)); 245 } 246 247 struct randomid_ctx * 248 randomid_new(int bits, long timeo) 249 { 250 struct randomconf *conf; 251 struct randomid_ctx *ctx; 252 253 if (timeo < RANDOMID_TIMEO_MIN) { 254 errno = EINVAL; 255 return (NULL); 256 } 257 258 for (conf = randomconf; conf->rc_bits > 0; conf++) { 259 if (bits == conf->rc_bits) 260 break; 261 } 262 263 /* unsupported bits */ 264 if (bits != conf->rc_bits) { 265 errno = ENOTSUP; 266 return (NULL); 267 } 268 269 ctx = malloc(sizeof(*ctx)); 270 memset(ctx, 0, sizeof(*ctx)); 271 ctx->ru_conf = conf; 272 ctx->ru_out = timeo; 273 274 return (ctx); 275 } 276 277 void 278 randomid_delete(struct randomid_ctx *ctx) 279 { 280 281 memset(ctx, 0, sizeof(*ctx)); 282 free(ctx); 283 } 284 285 u_int32_t 286 randomid(struct randomid_ctx *p) 287 { 288 int i, n; 289 u_int32_t tmp; 290 struct timeval tv; 291 292 gettimeofday(&tv, NULL); 293 if (p->ru_counter >= p->ru_max || tv.tv_sec > p->ru_reseed) 294 initid(p); 295 296 tmp = arc4random(); 297 298 /* Skip a random number of ids */ 299 n = tmp & 0x3; tmp = tmp >> 2; 300 if (p->ru_counter + n >= p->ru_max) 301 initid(p); 302 303 for (i = 0; i <= n; i++) { 304 /* Linear Congruential Generator */ 305 p->ru_x = (p->ru_a * p->ru_x + p->ru_b) % p->ru_m; 306 } 307 308 p->ru_counter += i; 309 310 return (p->ru_seed ^ pmod(p->ru_g, p->ru_seed2 ^ p->ru_x, p->ru_n)) | 311 p->ru_msb; 312 } 313
Indexes created Thu Sep 25 16:09:42 GMT 2025