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 "un-namespace.h" 36 37 struct arc4_stream { 38 u_int8_t i; 39 u_int8_t j; 40 u_int8_t s[256]; 41 }; 42 43 static int rs_initialized; 44 static struct arc4_stream rs; 45 46 static inline u_int8_t arc4_getbyte(struct arc4_stream *); 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, n; 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 * Throw away the first N bytes of output, as suggested in the 104 * paper "Weaknesses in the Key Scheduling Algorithm of RC4" 105 * by Fluher, Mantin, and Shamir. N=1024 is based on 106 * suggestions in the paper "(Not So) Random Shuffles of RC4" 107 * by Ilya Mironov. 108 */ 109 for (n = 0; n < 1024; n++) 110 arc4_getbyte(as); 111 } 112 113 static inline u_int8_t 114 arc4_getbyte(as) 115 struct arc4_stream *as; 116 { 117 u_int8_t si, sj; 118 119 as->i = (as->i + 1); 120 si = as->s[as->i]; 121 as->j = (as->j + si); 122 sj = as->s[as->j]; 123 as->s[as->i] = sj; 124 as->s[as->j] = si; 125 126 return (as->s[(si + sj) & 0xff]); 127 } 128 129 static inline u_int32_t 130 arc4_getword(as) 131 struct arc4_stream *as; 132 { 133 u_int32_t val; 134 135 val = arc4_getbyte(as) << 24; 136 val |= arc4_getbyte(as) << 16; 137 val |= arc4_getbyte(as) << 8; 138 val |= arc4_getbyte(as); 139 140 return (val); 141 } 142 143 void 144 arc4random_stir() 145 { 146 if (!rs_initialized) { 147 arc4_init(&rs); 148 rs_initialized = 1; 149 } 150 arc4_stir(&rs); 151 } 152 153 void 154 arc4random_addrandom(dat, datlen) 155 u_char *dat; 156 int datlen; 157 { 158 if (!rs_initialized) 159 arc4random_stir(); 160 arc4_addrandom(&rs, dat, datlen); 161 } 162 163 u_int32_t 164 arc4random() 165 { 166 if (!rs_initialized) 167 arc4random_stir(); 168 169 return (arc4_getword(&rs)); 170 } 171 172 #if 0 173 /*-------- Test code for i386 --------*/ 174 #include <stdio.h> 175 #include <machine/pctr.h> 176 int 177 main(int argc, char **argv) 178 { 179 const int iter = 1000000; 180 int i; 181 pctrval v; 182 183 v = rdtsc(); 184 for (i = 0; i < iter; i++) 185 arc4random(); 186 v = rdtsc() - v; 187 v /= iter; 188 189 printf("%qd cycles\n", v); 190 } 191 #endif 192