arc4random.c revision 169981
1/* 2 * Arc4 random number generator for OpenBSD. 3 * Copyright 1996 David Mazieres <dm@lcs.mit.edu>. 4 * 5 * Modification and redistribution in source and binary forms is 6 * permitted provided that due credit is given to the author and the 7 * OpenBSD project (for instance by leaving this copyright notice 8 * intact). 9 */ 10 11/* 12 * This code is derived from section 17.1 of Applied Cryptography, 13 * second edition, which describes a stream cipher allegedly 14 * compatible with RSA Labs "RC4" cipher (the actual description of 15 * which is a trade secret). The same algorithm is used as a stream 16 * cipher called "arcfour" in Tatu Ylonen's ssh package. 17 * 18 * Here the stream cipher has been modified always to include the time 19 * when initializing the state. That makes it impossible to 20 * regenerate the same random sequence twice, so this can't be used 21 * for encryption, but will generate good random numbers. 22 * 23 * RC4 is a registered trademark of RSA Laboratories. 24 */ 25 26#include <sys/cdefs.h> 27__FBSDID("$FreeBSD: head/lib/libc/gen/arc4random.c 169981 2007-05-25 10:40:33Z delphij $"); 28 29#include "namespace.h" 30#include <sys/types.h> 31#include <sys/time.h> 32#include <stdlib.h> 33#include <fcntl.h> 34#include <unistd.h> 35#include <pthread.h> 36 37#include "libc_private.h" 38#include "un-namespace.h" 39 40struct arc4_stream { 41 u_int8_t i; 42 u_int8_t j; 43 u_int8_t s[256]; 44}; 45 46static pthread_mutex_t arc4random_mtx = PTHREAD_MUTEX_INITIALIZER; 47 48#define RANDOMDEV "/dev/urandom" 49#define THREAD_LOCK() \ 50 do { \ 51 if (__isthreaded) \ 52 _pthread_mutex_lock(&arc4random_mtx); \ 53 } while (0) 54 55#define THREAD_UNLOCK() \ 56 do { \ 57 if (__isthreaded) \ 58 _pthread_mutex_unlock(&arc4random_mtx); \ 59 } while (0) 60 61static struct arc4_stream rs; 62static int rs_initialized; 63static int rs_stired; 64static int arc4_count; 65 66static inline u_int8_t arc4_getbyte(struct arc4_stream *); 67static void arc4_stir(struct arc4_stream *); 68 69static inline void 70arc4_init(struct arc4_stream *as) 71{ 72 int n; 73 74 for (n = 0; n < 256; n++) 75 as->s[n] = n; 76 as->i = 0; 77 as->j = 0; 78} 79 80static inline void 81arc4_addrandom(struct arc4_stream *as, u_char *dat, int datlen) 82{ 83 int n; 84 u_int8_t si; 85 86 as->i--; 87 for (n = 0; n < 256; n++) { 88 as->i = (as->i + 1); 89 si = as->s[as->i]; 90 as->j = (as->j + si + dat[n % datlen]); 91 as->s[as->i] = as->s[as->j]; 92 as->s[as->j] = si; 93 } 94} 95 96static void 97arc4_stir(struct arc4_stream *as) 98{ 99 int fd, n; 100 struct { 101 struct timeval tv; 102 pid_t pid; 103 u_int8_t rnd[128 - sizeof(struct timeval) - sizeof(pid_t)]; 104 } rdat; 105 106 gettimeofday(&rdat.tv, NULL); 107 rdat.pid = getpid(); 108 fd = _open(RANDOMDEV, O_RDONLY, 0); 109 if (fd >= 0) { 110 (void) _read(fd, rdat.rnd, sizeof(rdat.rnd)); 111 _close(fd); 112 } 113 /* fd < 0? Ah, what the heck. We'll just take whatever was on the 114 * stack... */ 115 116 arc4_addrandom(as, (void *) &rdat, sizeof(rdat)); 117 118 /* 119 * Throw away the first N bytes of output, as suggested in the 120 * paper "Weaknesses in the Key Scheduling Algorithm of RC4" 121 * by Fluher, Mantin, and Shamir. N=1024 is based on 122 * suggestions in the paper "(Not So) Random Shuffles of RC4" 123 * by Ilya Mironov. 124 */ 125 for (n = 0; n < 1024; n++) 126 (void) arc4_getbyte(as); 127 arc4_count = 400000; 128} 129 130static inline u_int8_t 131arc4_getbyte(struct arc4_stream *as) 132{ 133 u_int8_t si, sj; 134 135 as->i = (as->i + 1); 136 si = as->s[as->i]; 137 as->j = (as->j + si); 138 sj = as->s[as->j]; 139 as->s[as->i] = sj; 140 as->s[as->j] = si; 141 142 return (as->s[(si + sj) & 0xff]); 143} 144 145static inline u_int32_t 146arc4_getword(struct arc4_stream *as) 147{ 148 u_int32_t val; 149 150 val = arc4_getbyte(as) << 24; 151 val |= arc4_getbyte(as) << 16; 152 val |= arc4_getbyte(as) << 8; 153 val |= arc4_getbyte(as); 154 155 return (val); 156} 157 158static void 159arc4_check_init(void) 160{ 161 if (!rs_initialized) { 162 arc4_init(&rs); 163 rs_initialized = 1; 164 } 165} 166 167static void 168arc4_check_stir(void) 169{ 170 if (!rs_stired || --arc4_count == 0) { 171 arc4_stir(&rs); 172 rs_stired = 1; 173 } 174} 175 176void 177arc4random_stir(void) 178{ 179 THREAD_LOCK(); 180 arc4_check_init(); 181 arc4_stir(&rs); 182 THREAD_UNLOCK(); 183} 184 185void 186arc4random_addrandom(u_char *dat, int datlen) 187{ 188 THREAD_LOCK(); 189 arc4_check_init(); 190 arc4_check_stir(); 191 arc4_addrandom(&rs, dat, datlen); 192 THREAD_UNLOCK(); 193} 194 195u_int32_t 196arc4random(void) 197{ 198 u_int32_t rnd; 199 200 THREAD_LOCK(); 201 arc4_check_init(); 202 arc4_check_stir(); 203 rnd = arc4_getword(&rs); 204 THREAD_UNLOCK(); 205 206 return (rnd); 207} 208 209#if 0 210/*-------- Test code for i386 --------*/ 211#include <stdio.h> 212#include <machine/pctr.h> 213int 214main(int argc, char **argv) 215{ 216 const int iter = 1000000; 217 int i; 218 pctrval v; 219 220 v = rdtsc(); 221 for (i = 0; i < iter; i++) 222 arc4random(); 223 v = rdtsc() - v; 224 v /= iter; 225 226 printf("%qd cycles\n", v); 227} 228#endif 229