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("$FreeBSD$"); 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 40 struct arc4_stream { 41 u_int8_t i; 42 u_int8_t j; 43 u_int8_t s[256]; 44 }; 45 46 static 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 61 static struct arc4_stream rs; 62 static int rs_initialized; 63 static int rs_stired; 64 static int arc4_count; 65 66 static inline u_int8_t arc4_getbyte(struct arc4_stream *); 67 static void arc4_stir(struct arc4_stream *); 68 69 static inline void 70 arc4_init(as) 71 struct arc4_stream *as; 72 { 73 int n; 74 75 for (n = 0; n < 256; n++) 76 as->s[n] = n; 77 as->i = 0; 78 as->j = 0; 79 } 80 81 static inline void 82 arc4_addrandom(as, dat, datlen) 83 struct arc4_stream *as; 84 u_char *dat; 85 int datlen; 86 { 87 int n; 88 u_int8_t si; 89 90 as->i--; 91 for (n = 0; n < 256; n++) { 92 as->i = (as->i + 1); 93 si = as->s[as->i]; 94 as->j = (as->j + si + dat[n % datlen]); 95 as->s[as->i] = as->s[as->j]; 96 as->s[as->j] = si; 97 } 98 } 99 100 static void 101 arc4_stir(as) 102 struct arc4_stream *as; 103 { 104 int fd, n; 105 struct { 106 struct timeval tv; 107 pid_t pid; 108 u_int8_t rnd[128 - sizeof(struct timeval) - sizeof(pid_t)]; 109 } rdat; 110 111 gettimeofday(&rdat.tv, NULL); 112 rdat.pid = getpid(); 113 fd = _open(RANDOMDEV, O_RDONLY, 0); 114 if (fd >= 0) { 115 (void) _read(fd, rdat.rnd, sizeof(rdat.rnd)); 116 _close(fd); 117 } 118 /* fd < 0? Ah, what the heck. We'll just take whatever was on the 119 * stack... */ 120 121 arc4_addrandom(as, (void *) &rdat, sizeof(rdat)); 122 123 /* 124 * Throw away the first N bytes of output, as suggested in the 125 * paper "Weaknesses in the Key Scheduling Algorithm of RC4" 126 * by Fluher, Mantin, and Shamir. N=1024 is based on 127 * suggestions in the paper "(Not So) Random Shuffles of RC4" 128 * by Ilya Mironov. 129 */ 130 for (n = 0; n < 1024; n++) 131 (void) arc4_getbyte(as); 132 arc4_count = 400000; 133 } 134 135 static inline u_int8_t 136 arc4_getbyte(as) 137 struct arc4_stream *as; 138 { 139 u_int8_t si, sj; 140 141 as->i = (as->i + 1); 142 si = as->s[as->i]; 143 as->j = (as->j + si); 144 sj = as->s[as->j]; 145 as->s[as->i] = sj; 146 as->s[as->j] = si; 147 148 return (as->s[(si + sj) & 0xff]); 149 } 150 151 static inline u_int32_t 152 arc4_getword(as) 153 struct arc4_stream *as; 154 { 155 u_int32_t val; 156 157 val = arc4_getbyte(as) << 24; 158 val |= arc4_getbyte(as) << 16; 159 val |= arc4_getbyte(as) << 8; 160 val |= arc4_getbyte(as); 161 162 return (val); 163 } 164 165 static void 166 arc4_check_init(void) 167 { 168 if (!rs_initialized) { 169 arc4_init(&rs); 170 rs_initialized = 1; 171 } 172 } 173 174 static void 175 arc4_check_stir(void) 176 { 177 if (!rs_stired || --arc4_count == 0) { 178 arc4_stir(&rs); 179 rs_stired = 1; 180 } 181 } 182 183 void 184 arc4random_stir() 185 { 186 THREAD_LOCK(); 187 arc4_check_init(); 188 arc4_stir(&rs); 189 THREAD_UNLOCK(); 190 } 191 192 void 193 arc4random_addrandom(dat, datlen) 194 u_char *dat; 195 int datlen; 196 { 197 THREAD_LOCK(); 198 arc4_check_init(); 199 arc4_check_stir(); 200 arc4_addrandom(&rs, dat, datlen); 201 THREAD_UNLOCK(); 202 } 203 204 u_int32_t 205 arc4random() 206 { 207 u_int32_t rnd; 208 209 THREAD_LOCK(); 210 arc4_check_init(); 211 arc4_check_stir(); 212 rnd = arc4_getword(&rs); 213 THREAD_UNLOCK(); 214 215 return (rnd); 216 } 217 218 #if 0 219 /*-------- Test code for i386 --------*/ 220 #include <stdio.h> 221 #include <machine/pctr.h> 222 int 223 main(int argc, char **argv) 224 { 225 const int iter = 1000000; 226 int i; 227 pctrval v; 228 229 v = rdtsc(); 230 for (i = 0; i < iter; i++) 231 arc4random(); 232 v = rdtsc() - v; 233 v /= iter; 234 235 printf("%qd cycles\n", v); 236 } 237 #endif 238