1 /* $FreeBSD: src/lib/libc/gen/arc4random.c,v 1.4 2000/01/27 23:06:13 jasone Exp $ */ 2 /* $DragonFly: src/lib/libc/gen/arc4random.c,v 1.4 2004/06/19 18:55:47 joerg Exp $ */ 3 4 /* 5 * Arc4 random number generator for OpenBSD. 6 * Copyright 1996 David Mazieres <dm@lcs.mit.edu>. 7 * 8 * Modification and redistribution in source and binary forms is 9 * permitted provided that due credit is given to the author and the 10 * OpenBSD project (for instance by leaving this copyright notice 11 * intact). 12 */ 13 14 /* 15 * This code is derived from section 17.1 of Applied Cryptography, 16 * second edition, which describes a stream cipher allegedly 17 * compatible with RSA Labs "RC4" cipher (the actual description of 18 * which is a trade secret). The same algorithm is used as a stream 19 * cipher called "arcfour" in Tatu Ylonen's ssh package. 20 * 21 * Here the stream cipher has been modified always to include the time 22 * when initializing the state. That makes it impossible to 23 * regenerate the same random sequence twice, so this can't be used 24 * for encryption, but will generate good random numbers. 25 * 26 * RC4 is a registered trademark of RSA Laboratories. 27 */ 28 29 #include <stdlib.h> 30 #include <fcntl.h> 31 #include <unistd.h> 32 #include <sys/types.h> 33 #include <sys/time.h> 34 35 struct arc4_stream { 36 u_int8_t i; 37 u_int8_t j; 38 u_int8_t s[256]; 39 }; 40 41 static int rs_initialized; 42 static struct arc4_stream rs; 43 44 static inline u_int8_t arc4_getbyte(struct arc4_stream *); 45 46 static inline void 47 arc4_init(as) 48 struct arc4_stream *as; 49 { 50 int n; 51 52 for (n = 0; n < 256; n++) 53 as->s[n] = n; 54 as->i = 0; 55 as->j = 0; 56 } 57 58 static inline void 59 arc4_addrandom(as, dat, datlen) 60 struct arc4_stream *as; 61 u_char *dat; 62 int datlen; 63 { 64 int n; 65 u_int8_t si; 66 67 as->i--; 68 for (n = 0; n < 256; n++) { 69 as->i = (as->i + 1); 70 si = as->s[as->i]; 71 as->j = (as->j + si + dat[n % datlen]); 72 as->s[as->i] = as->s[as->j]; 73 as->s[as->j] = si; 74 } 75 } 76 77 static void 78 arc4_stir(as) 79 struct arc4_stream *as; 80 { 81 int fd, n; 82 struct { 83 struct timeval tv; 84 pid_t pid; 85 u_int8_t rnd[128 - sizeof(struct timeval) - sizeof(pid_t)]; 86 } rdat; 87 88 gettimeofday(&rdat.tv, NULL); 89 rdat.pid = getpid(); 90 fd = _open("/dev/urandom", O_RDONLY, 0); 91 if (fd >= 0) { 92 (void) _read(fd, rdat.rnd, sizeof(rdat.rnd)); 93 _close(fd); 94 } 95 /* fd < 0? Ah, what the heck. We'll just take whatever was on the 96 * stack... */ 97 98 arc4_addrandom(as, (void *) &rdat, sizeof(rdat)); 99 100 /* 101 * Throw away the first N bytes of output, as suggested in the 102 * paper "Weaknesses in the Key Scheduling Algorithm of RC4" 103 * by Fluher, Mantin, and Shamir. N=1024 is based on 104 * suggestions in the paper "(Not So) Random Shuffles of RC4" 105 * by Ilya Mironov. 106 */ 107 for (n = 0; n < 1024; n++) 108 arc4_getbyte(as); 109 } 110 111 static inline u_int8_t 112 arc4_getbyte(struct arc4_stream *as) 113 { 114 u_int8_t si, sj; 115 116 as->i = (as->i + 1); 117 si = as->s[as->i]; 118 as->j = (as->j + si); 119 sj = as->s[as->j]; 120 as->s[as->i] = sj; 121 as->s[as->j] = si; 122 return (as->s[(si + sj) & 0xff]); 123 } 124 125 static inline u_int32_t 126 arc4_getword(as) 127 struct arc4_stream *as; 128 { 129 u_int32_t val; 130 val = arc4_getbyte(as) << 24; 131 val |= arc4_getbyte(as) << 16; 132 val |= arc4_getbyte(as) << 8; 133 val |= arc4_getbyte(as); 134 return val; 135 } 136 137 void 138 arc4random_stir() 139 { 140 if (!rs_initialized) { 141 arc4_init(&rs); 142 rs_initialized = 1; 143 } 144 arc4_stir(&rs); 145 } 146 147 void 148 arc4random_addrandom(dat, datlen) 149 u_char *dat; 150 int datlen; 151 { 152 if (!rs_initialized) 153 arc4random_stir(); 154 arc4_addrandom(&rs, dat, datlen); 155 } 156 157 u_int32_t 158 arc4random() 159 { 160 if (!rs_initialized) 161 arc4random_stir(); 162 return arc4_getword(&rs); 163 } 164 165 #if 0 166 /*-------- Test code for i386 --------*/ 167 #include <stdio.h> 168 #include <machine/pctr.h> 169 int 170 main(int argc, char **argv) 171 { 172 const int iter = 1000000; 173 int i; 174 pctrval v; 175 176 v = rdtsc(); 177 for (i = 0; i < iter; i++) 178 arc4random(); 179 v = rdtsc() - v; 180 v /= iter; 181 182 printf("%qd cycles\n", v); 183 } 184 #endif 185