1 /* $NetBSD: randomid.c,v 1.16 2022/05/15 20:37:50 andvar 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 * 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 * Effectively 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/cdefs.h> 85 #if defined(LIBC_SCCS) && !defined(lint) 86 __RCSID("$NetBSD: randomid.c,v 1.16 2022/05/15 20:37:50 andvar Exp $"); 87 #endif 88 89 #include "namespace.h" 90 91 #include <sys/types.h> 92 #include <sys/time.h> 93 #include <stdlib.h> 94 #include <string.h> 95 #include <errno.h> 96 #include <randomid.h> 97 98 #ifdef __weak_alias 99 __weak_alias(randomid,_randomid) 100 __weak_alias(randomid_new,_randomid_new) 101 __weak_alias(randomid_delete,_randomid_delete) 102 #endif 103 104 struct randomconf { 105 const int rc_bits; /* resulting bits */ 106 const u_int32_t rc_max; /* Uniq cycle, avoid blackjack prediction */ 107 const u_int32_t rc_gen; /* Starting generator */ 108 const u_int32_t rc_n; /* ru_n: prime, ru_n - 1: product of pfacts[] */ 109 const u_int32_t rc_agen; /* determine ru_a as ru_agen^(2*rand) */ 110 const u_int32_t rc_m; /* ru_m = 2^x*3^y */ 111 const u_int32_t rc_pfacts[4]; /* factors of ru_n */ 112 const int rc_skip; /* skip values */ 113 }; 114 115 struct randomid_ctx { 116 struct randomconf *ru_conf; 117 #define ru_bits ru_conf->rc_bits 118 #define ru_max ru_conf->rc_max 119 #define ru_gen ru_conf->rc_gen 120 #define ru_n ru_conf->rc_n 121 #define ru_agen ru_conf->rc_agen 122 #define ru_m ru_conf->rc_m 123 #define ru_pfacts ru_conf->rc_pfacts 124 #define ru_skip ru_conf->rc_skip 125 long ru_out; /* Time after which will be reseeded */ 126 u_int32_t ru_counter; 127 u_int32_t ru_msb; 128 129 u_int32_t ru_x; 130 u_int32_t ru_seed, ru_seed2; 131 u_int32_t ru_a, ru_b; 132 u_int32_t ru_g; 133 time_t ru_reseed; 134 }; 135 136 static struct randomconf randomconf[] = { 137 { 138 32, /* resulting bits */ 139 1000000000, /* Uniq cycle, avoid blackjack prediction */ 140 2, /* Starting generator */ 141 2147483629, /* RU_N-1 = 2^2*3^2*59652323 */ 142 7, /* determine ru_a as RU_AGEN^(2*rand) */ 143 1836660096, /* RU_M = 2^7*3^15 - don't change */ 144 { 2, 3, 59652323, 0 }, /* factors of ru_n */ 145 3, /* skip values */ 146 }, 147 { 148 20, /* resulting bits */ 149 200000, /* Uniq cycle, avoid blackjack prediction */ 150 2, /* Starting generator */ 151 524269, /* RU_N-1 = 2^2*3^2*14563 */ 152 7, /* determine ru_a as RU_AGEN^(2*rand) */ 153 279936, /* RU_M = 2^7*3^7 - don't change */ 154 { 2, 3, 14563, 0 }, /* factors of ru_n */ 155 3, /* skip values */ 156 }, 157 { 158 16, /* resulting bits */ 159 30000, /* Uniq cycle, avoid blackjack prediction */ 160 2, /* Starting generator */ 161 32749, /* RU_N-1 = 2^2*3*2729 */ 162 7, /* determine ru_a as RU_AGEN^(2*rand) */ 163 31104, /* RU_M = 2^7*3^5 - don't change */ 164 { 2, 3, 2729, 0 }, /* factors of ru_n */ 165 0, /* skip values */ 166 }, 167 { 168 .rc_bits = -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 * Initializes 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() & (~0U >> (32 - p->ru_bits))) | 1; 225 p->ru_a = pmod(p->ru_agen, 226 (arc4random() & (~0U >> (32 - p->ru_bits))) & (~1U), p->ru_m); 227 while (p->ru_b % 3 == 0) 228 p->ru_b += 2; 229 230 j = arc4random() % p->ru_n; 231 232 /* 233 * Do a fast gcd(j, RU_N - 1), so we can find a j with 234 * gcd(j, RU_N - 1) == 1, giving a new generator for 235 * RU_GEN^j mod RU_N 236 */ 237 while (noprime) { 238 for (i = 0; p->ru_pfacts[i] > 0; i++) 239 if (j % p->ru_pfacts[i] == 0) 240 break; 241 242 if (p->ru_pfacts[i] == 0) 243 noprime = 0; 244 else 245 j = (j + 1) % p->ru_n; 246 } 247 248 p->ru_g = pmod(p->ru_gen, j, p->ru_n); 249 p->ru_counter = 0; 250 251 gettimeofday(&tv, NULL); 252 p->ru_reseed = tv.tv_sec + p->ru_out; 253 p->ru_msb = p->ru_msb ? 0 : (1U << (p->ru_bits - 1)); 254 } 255 256 struct randomid_ctx * 257 randomid_new(int bits, long timeo) 258 { 259 struct randomconf *conf; 260 struct randomid_ctx *ctx; 261 262 if (timeo < RANDOMID_TIMEO_MIN) { 263 errno = EINVAL; 264 return (NULL); 265 } 266 267 for (conf = randomconf; conf->rc_bits > 0; conf++) { 268 if (bits == conf->rc_bits) 269 break; 270 } 271 272 /* unsupported bits */ 273 if (bits != conf->rc_bits) { 274 errno = ENOTSUP; 275 return (NULL); 276 } 277 278 ctx = malloc(sizeof(*ctx)); 279 if (!ctx) 280 return (NULL); 281 282 memset(ctx, 0, sizeof(*ctx)); 283 ctx->ru_conf = conf; 284 ctx->ru_out = timeo; 285 286 return (ctx); 287 } 288 289 void 290 randomid_delete(struct randomid_ctx *ctx) 291 { 292 293 memset(ctx, 0, sizeof(*ctx)); 294 free(ctx); 295 } 296 297 u_int32_t 298 randomid(struct randomid_ctx *p) 299 { 300 int i, n; 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 /* Skip a random number of ids */ 308 if (p->ru_skip) { 309 n = arc4random() & p->ru_skip; 310 if (p->ru_counter + n >= p->ru_max) 311 initid(p); 312 } else 313 n = 0; 314 315 for (i = 0; i <= n; i++) { 316 /* Linear Congruential Generator */ 317 p->ru_x = (u_int32_t)(((u_int64_t)p->ru_a * p->ru_x + p->ru_b) % p->ru_m); 318 } 319 320 p->ru_counter += i; 321 322 return (p->ru_seed ^ pmod(p->ru_g, p->ru_seed2 + p->ru_x, p->ru_n)) | 323 p->ru_msb; 324 } 325
Indexes created Wed Sep 24 22:09:59 GMT 2025