1 /* $NetBSD: arc4random.c,v 1.4 2002/07/02 17:10:19 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 int n; 99 100 gettimeofday(&rdat.tv, NULL); 101 fd = open("/dev/urandom", O_RDONLY); 102 if (fd != -1) { 103 read(fd, rdat.rnd, sizeof(rdat.rnd)); 104 close(fd); 105 } 106 #ifdef KERN_URND 107 else { 108 int i, mib[2]; 109 size_t len; 110 111 /* Device could not be opened, we might be chrooted, take 112 * randomness from sysctl. */ 113 114 mib[0] = CTL_KERN; 115 mib[1] = KERN_URND; 116 117 for (i = 0; i < sizeof(rdat.rnd) / sizeof(u_int); i ++) { 118 len = sizeof(u_int); 119 if (sysctl(mib, 2, &rdat.rnd[i], &len, NULL, 0) == -1) 120 break; 121 } 122 } 123 #endif 124 /* fd < 0 or failed sysctl ? Ah, what the heck. We'll just take 125 * whatever was on the stack... */ 126 127 arc4_addrandom(as, (void *) &rdat, sizeof(rdat)); 128 129 /* 130 * Throw away the first N words of output, as suggested in the 131 * paper "Weaknesses in the Key Scheduling Algorithm of RC4" 132 * by Fluher, Mantin, and Shamir. (N = 256 in our case.) 133 */ 134 for (n = 0; n < 256 * 4; n++) 135 arc4_getbyte(as); 136 } 137 138 static inline u_int8_t 139 arc4_getbyte(as) 140 struct arc4_stream *as; 141 { 142 u_int8_t si, sj; 143 144 as->i = (as->i + 1); 145 si = as->s[as->i]; 146 as->j = (as->j + si); 147 sj = as->s[as->j]; 148 as->s[as->i] = sj; 149 as->s[as->j] = si; 150 return (as->s[(si + sj) & 0xff]); 151 } 152 153 static inline u_int32_t 154 arc4_getword(as) 155 struct arc4_stream *as; 156 { 157 u_int32_t val; 158 val = arc4_getbyte(as) << 24; 159 val |= arc4_getbyte(as) << 16; 160 val |= arc4_getbyte(as) << 8; 161 val |= arc4_getbyte(as); 162 return val; 163 } 164 165 void 166 arc4random_stir() 167 { 168 if (!rs_initialized) { 169 arc4_init(&rs); 170 rs_initialized = 1; 171 } 172 arc4_stir(&rs); 173 } 174 175 void 176 arc4random_addrandom(dat, datlen) 177 u_char *dat; 178 int datlen; 179 { 180 if (!rs_initialized) 181 arc4random_stir(); 182 arc4_addrandom(&rs, dat, datlen); 183 } 184 185 u_int32_t 186 arc4random() 187 { 188 if (!rs_initialized) 189 arc4random_stir(); 190 return arc4_getword(&rs); 191 } 192 193 #if 0 194 /*-------- Test code for i386 --------*/ 195 #include <stdio.h> 196 #include <machine/pctr.h> 197 int 198 main(int argc, char **argv) 199 { 200 const int iter = 1000000; 201 int i; 202 pctrval v; 203 204 v = rdtsc(); 205 for (i = 0; i < iter; i++) 206 arc4random(); 207 v = rdtsc() - v; 208 v /= iter; 209 210 printf("%qd cycles\n", v); 211 } 212 #endif 213