1 /* $NetBSD: arc4random.c,v 1.2 2002/05/24 04:53:07 itojun Exp $ */ 2 /* $OpenBSD: arc4random.c,v 1.6 2001/06/05 05:05:38 pvalchev 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 by leaving this copyright notice 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 <fcntl.h> 29 #include <stdlib.h> 30 #include <unistd.h> 31 #include <sys/types.h> 32 #include <sys/param.h> 33 #include <sys/time.h> 34 #include <sys/sysctl.h> 35 36 #ifdef __GNUC__ 37 #define inline __inline 38 #else /* !__GNUC__ */ 39 #define inline 40 #endif /* !__GNUC__ */ 41 42 struct arc4_stream { 43 u_int8_t i; 44 u_int8_t j; 45 u_int8_t s[256]; 46 }; 47 48 int rs_initialized; 49 static struct arc4_stream rs; 50 51 static inline void arc4_init(struct arc4_stream *); 52 static inline void arc4_addrandom(struct arc4_stream *, u_char *, int); 53 static void arc4_stir(struct arc4_stream *); 54 static inline u_int8_t arc4_getbyte(struct arc4_stream *); 55 static inline u_int32_t arc4_getword(struct arc4_stream *); 56 57 static inline void 58 arc4_init(as) 59 struct arc4_stream *as; 60 { 61 int n; 62 63 for (n = 0; n < 256; n++) 64 as->s[n] = n; 65 as->i = 0; 66 as->j = 0; 67 } 68 69 static inline void 70 arc4_addrandom(as, dat, datlen) 71 struct arc4_stream *as; 72 u_char *dat; 73 int datlen; 74 { 75 int n; 76 u_int8_t si; 77 78 as->i--; 79 for (n = 0; n < 256; n++) { 80 as->i = (as->i + 1); 81 si = as->s[as->i]; 82 as->j = (as->j + si + dat[n % datlen]); 83 as->s[as->i] = as->s[as->j]; 84 as->s[as->j] = si; 85 } 86 as->j = as->i; 87 } 88 89 static void 90 arc4_stir(as) 91 struct arc4_stream *as; 92 { 93 int fd; 94 struct { 95 struct timeval tv; 96 u_int rnd[(128 - sizeof(struct timeval)) / sizeof(u_int)]; 97 } rdat; 98 99 gettimeofday(&rdat.tv, NULL); 100 fd = open("/dev/urandom", O_RDONLY); 101 if (fd != -1) { 102 read(fd, rdat.rnd, sizeof(rdat.rnd)); 103 close(fd); 104 } 105 #ifdef KERN_ARND 106 else { 107 int i, mib[2]; 108 size_t len; 109 110 /* Device could not be opened, we might be chrooted, take 111 * randomness from sysctl. */ 112 113 mib[0] = CTL_KERN; 114 mib[1] = KERN_ARND; 115 116 for (i = 0; i < sizeof(rdat.rnd) / sizeof(u_int); i ++) { 117 len = sizeof(u_int); 118 if (sysctl(mib, 2, &rdat.rnd[i], &len, NULL, 0) == -1) 119 break; 120 } 121 } 122 #endif 123 /* fd < 0 or failed sysctl ? Ah, what the heck. We'll just take 124 * whatever was on the stack... */ 125 126 arc4_addrandom(as, (void *) &rdat, sizeof(rdat)); 127 } 128 129 static inline u_int8_t 130 arc4_getbyte(as) 131 struct arc4_stream *as; 132 { 133 u_int8_t si, sj; 134 135 as->i = (as->i + 1); 136 si = as->s[as->i]; 137 as->j = (as->j + si); 138 sj = as->s[as->j]; 139 as->s[as->i] = sj; 140 as->s[as->j] = si; 141 return (as->s[(si + sj) & 0xff]); 142 } 143 144 static inline u_int32_t 145 arc4_getword(as) 146 struct arc4_stream *as; 147 { 148 u_int32_t val; 149 val = arc4_getbyte(as) << 24; 150 val |= arc4_getbyte(as) << 16; 151 val |= arc4_getbyte(as) << 8; 152 val |= arc4_getbyte(as); 153 return val; 154 } 155 156 void 157 arc4random_stir() 158 { 159 if (!rs_initialized) { 160 arc4_init(&rs); 161 rs_initialized = 1; 162 } 163 arc4_stir(&rs); 164 } 165 166 void 167 arc4random_addrandom(dat, datlen) 168 u_char *dat; 169 int datlen; 170 { 171 if (!rs_initialized) 172 arc4random_stir(); 173 arc4_addrandom(&rs, dat, datlen); 174 } 175 176 u_int32_t 177 arc4random() 178 { 179 if (!rs_initialized) 180 arc4random_stir(); 181 return arc4_getword(&rs); 182 } 183 184 #if 0 185 /*-------- Test code for i386 --------*/ 186 #include <stdio.h> 187 #include <machine/pctr.h> 188 int 189 main(int argc, char **argv) 190 { 191 const int iter = 1000000; 192 int i; 193 pctrval v; 194 195 v = rdtsc(); 196 for (i = 0; i < iter; i++) 197 arc4random(); 198 v = rdtsc() - v; 199 v /= iter; 200 201 printf("%qd cycles\n", v); 202 } 203 #endif 204