1 /* $FreeBSD$ */ 2 3 /* 4 * Arc4 random number generator for OpenBSD. 5 * Copyright 1996 David Mazieres <dm@lcs.mit.edu>. 6 * 7 * Modification and redistribution in source and binary forms is 8 * permitted provided that due credit is given to the author and the 9 * OpenBSD project (for instance by leaving this copyright notice 10 * intact). 11 */ 12 13 /* 14 * This code is derived from section 17.1 of Applied Cryptography, 15 * second edition, which describes a stream cipher allegedly 16 * compatible with RSA Labs "RC4" cipher (the actual description of 17 * which is a trade secret). The same algorithm is used as a stream 18 * cipher called "arcfour" in Tatu Ylonen's ssh package. 19 * 20 * Here the stream cipher has been modified always to include the time 21 * when initializing the state. That makes it impossible to 22 * regenerate the same random sequence twice, so this can't be used 23 * for encryption, but will generate good random numbers. 24 * 25 * RC4 is a registered trademark of RSA Laboratories. 26 */ 27 28 #include <sys/cdefs.h> 29 __FBSDID("$FreeBSD$"); 30 31 #include "namespace.h" 32 #include <sys/types.h> 33 #include <sys/time.h> 34 #include <stdlib.h> 35 #include <fcntl.h> 36 #include <unistd.h> 37 #include "un-namespace.h" 38 39 struct arc4_stream { 40 u_int8_t i; 41 u_int8_t j; 42 u_int8_t s[256]; 43 }; 44 45 static int rs_initialized; 46 static struct arc4_stream rs; 47 48 static inline void 49 arc4_init(as) 50 struct arc4_stream *as; 51 { 52 int n; 53 54 for (n = 0; n < 256; n++) 55 as->s[n] = n; 56 as->i = 0; 57 as->j = 0; 58 } 59 60 static inline void 61 arc4_addrandom(as, dat, datlen) 62 struct arc4_stream *as; 63 u_char *dat; 64 int datlen; 65 { 66 int n; 67 u_int8_t si; 68 69 as->i--; 70 for (n = 0; n < 256; n++) { 71 as->i = (as->i + 1); 72 si = as->s[as->i]; 73 as->j = (as->j + si + dat[n % datlen]); 74 as->s[as->i] = as->s[as->j]; 75 as->s[as->j] = si; 76 } 77 } 78 79 static void 80 arc4_stir(as) 81 struct arc4_stream *as; 82 { 83 int fd; 84 struct { 85 struct timeval tv; 86 pid_t pid; 87 u_int8_t rnd[128 - sizeof(struct timeval) - sizeof(pid_t)]; 88 } rdat; 89 90 gettimeofday(&rdat.tv, NULL); 91 rdat.pid = getpid(); 92 fd = _open("/dev/urandom", O_RDONLY, 0); 93 if (fd >= 0) { 94 (void) _read(fd, rdat.rnd, sizeof(rdat.rnd)); 95 _close(fd); 96 } 97 /* fd < 0? Ah, what the heck. We'll just take whatever was on the 98 * stack... */ 99 100 arc4_addrandom(as, (void *) &rdat, sizeof(rdat)); 101 } 102 103 static inline u_int8_t 104 arc4_getbyte(as) 105 struct arc4_stream *as; 106 { 107 u_int8_t si, sj; 108 109 as->i = (as->i + 1); 110 si = as->s[as->i]; 111 as->j = (as->j + si); 112 sj = as->s[as->j]; 113 as->s[as->i] = sj; 114 as->s[as->j] = si; 115 return (as->s[(si + sj) & 0xff]); 116 } 117 118 static inline u_int32_t 119 arc4_getword(as) 120 struct arc4_stream *as; 121 { 122 u_int32_t val; 123 val = arc4_getbyte(as) << 24; 124 val |= arc4_getbyte(as) << 16; 125 val |= arc4_getbyte(as) << 8; 126 val |= arc4_getbyte(as); 127 return val; 128 } 129 130 void 131 arc4random_stir() 132 { 133 if (!rs_initialized) { 134 arc4_init(&rs); 135 rs_initialized = 1; 136 } 137 arc4_stir(&rs); 138 } 139 140 void 141 arc4random_addrandom(dat, datlen) 142 u_char *dat; 143 int datlen; 144 { 145 if (!rs_initialized) 146 arc4random_stir(); 147 arc4_addrandom(&rs, dat, datlen); 148 } 149 150 u_int32_t 151 arc4random() 152 { 153 if (!rs_initialized) 154 arc4random_stir(); 155 return arc4_getword(&rs); 156 } 157 158 #if 0 159 /*-------- Test code for i386 --------*/ 160 #include <stdio.h> 161 #include <machine/pctr.h> 162 int 163 main(int argc, char **argv) 164 { 165 const int iter = 1000000; 166 int i; 167 pctrval v; 168 169 v = rdtsc(); 170 for (i = 0; i < iter; i++) 171 arc4random(); 172 v = rdtsc() - v; 173 v /= iter; 174 175 printf("%qd cycles\n", v); 176 } 177 #endif 178