1/* 2 * Copyright (c) 1996, David Mazieres <dm@uun.org> 3 * Copyright (c) 2008, Damien Miller <djm@openbsd.org> 4 * 5 * Permission to use, copy, modify, and distribute this software for any 6 * purpose with or without fee is hereby granted, provided that the above 7 * copyright notice and this permission notice appear in all copies. 8 * 9 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 10 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 11 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 12 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 13 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 14 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 15 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 16 */ 17 18/* 19 * Arc4 random number generator for OpenBSD. 20 * 21 * This code is derived from section 17.1 of Applied Cryptography, 22 * second edition, which describes a stream cipher allegedly 23 * compatible with RSA Labs "RC4" cipher (the actual description of 24 * which is a trade secret). The same algorithm is used as a stream 25 * cipher called "arcfour" in Tatu Ylonen's ssh package. 26 * 27 * Here the stream cipher has been modified always to include the time 28 * when initializing the state. That makes it impossible to 29 * regenerate the same random sequence twice, so this can't be used 30 * for encryption, but will generate good random numbers. 31 * 32 * RC4 is a registered trademark of RSA Laboratories. 33 */ 34 35#include <sys/cdefs.h> 36__FBSDID("$FreeBSD: src/lib/libc/gen/arc4random.c,v 1.25 2008/09/09 09:46:36 ache Exp $"); 37 38#include "namespace.h" 39#include <sys/types.h> 40#include <sys/time.h> 41#include <stdlib.h> 42#include <fcntl.h> 43#include <unistd.h> 44#include <pthread.h> 45 46#include "libc_private.h" 47#include "un-namespace.h" 48 49struct arc4_stream { 50 u_int8_t i; 51 u_int8_t j; 52 u_int8_t s[256]; 53}; 54 55static int lock = 0; 56extern void spin_lock(int*); 57extern void spin_unlock(int*); 58 59#define RANDOMDEV "/dev/random" 60#define KEYSIZE 128 61#define THREAD_LOCK() \ 62 do { \ 63 if (__isthreaded) \ 64 spin_lock(&lock); \ 65 } while (0) 66 67#define THREAD_UNLOCK() \ 68 do { \ 69 if (__isthreaded) \ 70 spin_unlock(&lock); \ 71 } while (0) 72 73static struct arc4_stream rs = { 74 .i = 0, 75 .j = 0, 76 .s = { 77 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 78 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 79 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 80 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 81 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 82 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 83 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 84 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 85 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 86 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 87 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 88 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191, 89 192, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207, 90 208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 218, 219, 220, 221, 222, 223, 91 224, 225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239, 92 240, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255 93 } 94}; 95static int rs_stired; 96static int arc4_count; 97 98static inline u_int8_t arc4_getbyte(void); 99static void arc4_stir(void); 100 101static struct { 102 struct timeval tv; 103 pid_t pid; 104 u_int8_t rnd[KEYSIZE]; 105} rdat; 106static volatile int rs_data_available = 0; 107 108static inline void 109arc4_addrandom(u_char *dat, int datlen) 110{ 111 int n; 112 u_int8_t si; 113 114 rs.i--; 115 for (n = 0; n < 256; n++) { 116 rs.i = (rs.i + 1); 117 si = rs.s[rs.i]; 118 rs.j = (rs.j + si + dat[n % datlen]); 119 rs.s[rs.i] = rs.s[rs.j]; 120 rs.s[rs.j] = si; 121 } 122 rs.j = rs.i; 123} 124 125static void 126arc4_fetch(void) 127{ 128 int done, fd; 129 fd = _open(RANDOMDEV, O_RDONLY, 0); 130 done = 0; 131 if (fd >= 0) { 132 if (_read(fd, &rdat, KEYSIZE) == KEYSIZE) 133 done = 1; 134 (void)_close(fd); 135 } 136 if (!done) { 137 (void)gettimeofday(&rdat.tv, NULL); 138 rdat.pid = getpid(); 139 /* We'll just take whatever was on the stack too... */ 140 } 141} 142 143static void 144arc4_stir(void) 145{ 146 int n; 147 /* 148 * If we don't have data, we need some now before we can integrate 149 * it into the static buffers 150 */ 151 if (!rs_data_available) 152 { 153 arc4_fetch(); 154 } 155 rs_data_available = 0; 156 __sync_synchronize(); 157 158 arc4_addrandom((u_char *)&rdat, KEYSIZE); 159 160 /* 161 * Throw away the first N bytes of output, as suggested in the 162 * paper "Weaknesses in the Key Scheduling Algorithm of RC4" 163 * by Fluher, Mantin, and Shamir. N=1024 is based on 164 * suggestions in the paper "(Not So) Random Shuffles of RC4" 165 * by Ilya Mironov. 166 */ 167 for (n = 0; n < 1024; n++) 168 (void) arc4_getbyte(); 169 arc4_count = 1600000; 170 rs_stired = 1; 171} 172 173static inline u_int8_t 174arc4_getbyte(void) 175{ 176 u_int8_t si, sj; 177 178 rs.i = (rs.i + 1); 179 si = rs.s[rs.i]; 180 rs.j = (rs.j + si); 181 sj = rs.s[rs.j]; 182 rs.s[rs.i] = sj; 183 rs.s[rs.j] = si; 184 185 return (rs.s[(si + sj) & 0xff]); 186} 187 188static inline u_int32_t 189arc4_getword(void) 190{ 191 u_int32_t val; 192 193 val = arc4_getbyte() << 24; 194 val |= arc4_getbyte() << 16; 195 val |= arc4_getbyte() << 8; 196 val |= arc4_getbyte(); 197 198 return (val); 199} 200 201/* 7944700: force restir in child */ 202__private_extern__ void 203_arc4_fork_child(void) 204{ 205 rs_stired = 0; 206 rs_data_available = 0; 207} 208 209static inline int 210arc4_check_stir(void) 211{ 212 if (!rs_stired || arc4_count <= 0) { 213 arc4_stir(); 214 return 1; 215 } 216 return 0; 217} 218 219void 220arc4random_stir(void) 221{ 222 THREAD_LOCK(); 223 arc4_stir(); 224 THREAD_UNLOCK(); 225} 226 227void 228arc4random_addrandom(u_char *dat, int datlen) 229{ 230 THREAD_LOCK(); 231 arc4_check_stir(); 232 arc4_addrandom(dat, datlen); 233 THREAD_UNLOCK(); 234} 235 236u_int32_t 237arc4random(void) 238{ 239 u_int32_t rnd; 240 241 THREAD_LOCK(); 242 243 int did_stir = arc4_check_stir(); 244 rnd = arc4_getword(); 245 arc4_count -= 4; 246 247 THREAD_UNLOCK(); 248 if (did_stir) 249 { 250 /* stirring used up our data pool, we need to read in new data outside of the lock */ 251 arc4_fetch(); 252 rs_data_available = 1; 253 __sync_synchronize(); 254 } 255 256 return (rnd); 257} 258 259void 260arc4random_buf(void *_buf, size_t n) 261{ 262 u_char *buf = (u_char *)_buf; 263 int did_stir = 0; 264 265 THREAD_LOCK(); 266 267 while (n--) { 268 if (arc4_check_stir()) 269 { 270 did_stir = 1; 271 } 272 buf[n] = arc4_getbyte(); 273 arc4_count--; 274 } 275 276 THREAD_UNLOCK(); 277 if (did_stir) 278 { 279 /* stirring used up our data pool, we need to read in new data outside of the lock */ 280 arc4_fetch(); 281 rs_data_available = 1; 282 __sync_synchronize(); 283 } 284} 285 286/* 287 * Calculate a uniformly distributed random number less than upper_bound 288 * avoiding "modulo bias". 289 * 290 * Uniformity is achieved by generating new random numbers until the one 291 * returned is outside the range [0, 2**32 % upper_bound). This 292 * guarantees the selected random number will be inside 293 * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound) 294 * after reduction modulo upper_bound. 295 */ 296u_int32_t 297arc4random_uniform(u_int32_t upper_bound) 298{ 299 u_int32_t r, min; 300 301 if (upper_bound < 2) 302 return (0); 303 304#if (ULONG_MAX > 0xffffffffUL) 305 min = 0x100000000UL % upper_bound; 306#else 307 /* Calculate (2**32 % upper_bound) avoiding 64-bit math */ 308 if (upper_bound > 0x80000000) 309 min = 1 + ~upper_bound; /* 2**32 - upper_bound */ 310 else { 311 /* (2**32 - (x * 2)) % x == 2**32 % x when x <= 2**31 */ 312 min = ((0xffffffff - (upper_bound * 2)) + 1) % upper_bound; 313 } 314#endif 315 316 /* 317 * This could theoretically loop forever but each retry has 318 * p > 0.5 (worst case, usually far better) of selecting a 319 * number inside the range we need, so it should rarely need 320 * to re-roll. 321 */ 322 for (;;) { 323 r = arc4random(); 324 if (r >= min) 325 break; 326 } 327 328 return (r % upper_bound); 329} 330 331#if 0 332/*-------- Test code for i386 --------*/ 333#include <stdio.h> 334#include <machine/pctr.h> 335int 336main(int argc, char **argv) 337{ 338 const int iter = 1000000; 339 int i; 340 pctrval v; 341 342 v = rdtsc(); 343 for (i = 0; i < iter; i++) 344 arc4random(); 345 v = rdtsc() - v; 346 v /= iter; 347 348 printf("%qd cycles\n", v); 349} 350#endif 351