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