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 <stdlib.h> 29 #include <fcntl.h> 30 #include <unistd.h> 31 #include <sys/types.h> 32 #include <sys/time.h> 33 34 struct arc4_stream { 35 u_int8_t i; 36 u_int8_t j; 37 u_int8_t s[256]; 38 }; 39 40 static int rs_initialized; 41 static struct arc4_stream rs; 42 43 static inline void 44 arc4_init(as) 45 struct arc4_stream *as; 46 { 47 int n; 48 49 for (n = 0; n < 256; n++) 50 as->s[n] = n; 51 as->i = 0; 52 as->j = 0; 53 } 54 55 static inline void 56 arc4_addrandom(as, dat, datlen) 57 struct arc4_stream *as; 58 u_char *dat; 59 int datlen; 60 { 61 int n; 62 u_int8_t si; 63 64 as->i--; 65 for (n = 0; n < 256; n++) { 66 as->i = (as->i + 1); 67 si = as->s[as->i]; 68 as->j = (as->j + si + dat[n % datlen]); 69 as->s[as->i] = as->s[as->j]; 70 as->s[as->j] = si; 71 } 72 } 73 74 static void 75 arc4_stir(as) 76 struct arc4_stream *as; 77 { 78 int fd; 79 struct { 80 struct timeval tv; 81 pid_t pid; 82 u_int8_t rnd[128 - sizeof(struct timeval) - sizeof(pid_t)]; 83 } rdat; 84 85 gettimeofday(&rdat.tv, NULL); 86 rdat.pid = getpid(); 87 fd = _open("/dev/urandom", O_RDONLY, 0); 88 if (fd >= 0) { 89 (void) _read(fd, rdat.rnd, sizeof(rdat.rnd)); 90 _close(fd); 91 } 92 /* fd < 0? Ah, what the heck. We'll just take whatever was on the 93 * stack... */ 94 95 arc4_addrandom(as, (void *) &rdat, sizeof(rdat)); 96 } 97 98 static inline u_int8_t 99 arc4_getbyte(as) 100 struct arc4_stream *as; 101 { 102 u_int8_t si, sj; 103 104 as->i = (as->i + 1); 105 si = as->s[as->i]; 106 as->j = (as->j + si); 107 sj = as->s[as->j]; 108 as->s[as->i] = sj; 109 as->s[as->j] = si; 110 return (as->s[(si + sj) & 0xff]); 111 } 112 113 static inline u_int32_t 114 arc4_getword(as) 115 struct arc4_stream *as; 116 { 117 u_int32_t val; 118 val = arc4_getbyte(as) << 24; 119 val |= arc4_getbyte(as) << 16; 120 val |= arc4_getbyte(as) << 8; 121 val |= arc4_getbyte(as); 122 return val; 123 } 124 125 void 126 arc4random_stir() 127 { 128 if (!rs_initialized) { 129 arc4_init(&rs); 130 rs_initialized = 1; 131 } 132 arc4_stir(&rs); 133 } 134 135 void 136 arc4random_addrandom(dat, datlen) 137 u_char *dat; 138 int datlen; 139 { 140 if (!rs_initialized) 141 arc4random_stir(); 142 arc4_addrandom(&rs, dat, datlen); 143 } 144 145 u_int32_t 146 arc4random() 147 { 148 if (!rs_initialized) 149 arc4random_stir(); 150 return arc4_getword(&rs); 151 } 152 153 #if 0 154 /*-------- Test code for i386 --------*/ 155 #include <stdio.h> 156 #include <machine/pctr.h> 157 int 158 main(int argc, char **argv) 159 { 160 const int iter = 1000000; 161 int i; 162 pctrval v; 163 164 v = rdtsc(); 165 for (i = 0; i < iter; i++) 166 arc4random(); 167 v = rdtsc() - v; 168 v /= iter; 169 170 printf("%qd cycles\n", v); 171 } 172 #endif 173