Turns out native android development doesn’t supply you with a real ar4random method. However adapting the OpenBSD’s arc4random.c does the trick. And even works on windows without using CryptoAPI (thanks to Chris K. Jester-Young for these suggestions). Additionally with boost *ducks* it should be more or less multithreadsafe.
Mixed (red dots are generated by arc4; Math.Random() Arc4random)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 | /* $OpenBSD: arc4random.c,v 1.24 2013/06/11 16:59:50 deraadt Exp $ */ /* * Copyright (c) 1996, David Mazieres <dm@uun.org> * Copyright (c) 2008, Damien Miller <djm@openbsd.org> * * Permission to use, copy, modify, and distribute this software for any * purpose with or without fee is hereby granted, provided that the above * copyright notice and this permission notice appear in all copies. * * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */ /* * Arc4 random number generator for OpenBSD. * * This code is derived from section 17.1 of Applied Cryptography, * second edition, which describes a stream cipher allegedly * compatible with RSA Labs "RC4" cipher (the actual description of * which is a trade secret). The same algorithm is used as a stream * cipher called "arcfour" in Tatu Ylonen's ssh package. * * RC4 is a registered trademark of RSA Laboratories. */ #include <boost\thread.hpp> #if (CC_TARGET_PLATFORM == CC_PLATFORM_WIN32) #include <Windows.h> #endif typedef uint8_t u_int8_t; typedef uint16_t u_int16_t; typedef uint32_t u_int32_t; typedef uint64_t u_int64_t; typedef unsigned char u_char; struct arc4_stream { u_int8_t i; u_int8_t j; u_int8_t s[256]; }; #define pid_t boost::thread::id static int rs_initialized; static struct arc4_stream rs; static pid_t arc4_stir_pid; static int arc4_count; static inline u_int8_t arc4_getbyte(void); static inline void arc4_init(void) { int n; for (n = 0; n < 256; n++) rs.s[n] = n; rs.i = 0; rs.j = 0; } static inline void arc4_addrandom(u_char *dat, int datlen) { int n; u_int8_t si; rs.i--; for (n = 0; n < 256; n++) { rs.i = (rs.i + 1); si = rs.s[rs.i]; rs.j = (rs.j + si + dat[n % datlen]); rs.s[rs.i] = rs.s[rs.j]; rs.s[rs.j] = si; } rs.j = rs.i; } static const char * urandom = "/dev/urandom"; static void fillRandom(u_char *rnd, size_t len) { for (int i = 0; i < (int)len; ++i) rnd[i] = i & 255; for (int k = 0; k < (int)len*8; ++k) { int v1 = rand() % len; int v2 = rand() % len; u_char temp = rnd[v1]; rnd[v1] = rnd[v2]; rnd[v2] = temp; } } static void arc4_stir(void) { int i; u_char rnd[128]; if (!rs_initialized) { arc4_init(); rs_initialized = 1; } #if (CC_TARGET_PLATFORM == CC_PLATFORM_WIN32) HMODULE hLib=LoadLibraryA("ADVAPI32.DLL"); if (hLib) { BOOLEAN (APIENTRY *pfn)(void*, ULONG) = (BOOLEAN (APIENTRY *)(void*,ULONG))GetProcAddress(hLib,"SystemFunction036"); if (pfn) { if(pfn(rnd,sizeof(rnd))) { // use buff full of random goop } } FreeLibrary(hLib); } #elif (CC_TARGET_PLATFORM == CC_PLATFORM_ANDROID) size_t len = sizeof(rnd); // open /dev/urandom and read 128 bytes FILE *in = fopen(urandom,"r"); if (in == NULL) { CCLog("Couldn't open file %s", urandom); fillRandom(rnd,len); } else { size_t ret = fread(rnd,1,len,in); if(ret != len) { CCLog("%d != %d", ret, len); fillRandom(rnd,len); } fclose(in); } #elif (CC_TARGET_PLATFORM == CC_PLATFORM_LINUX) int mib[2]; // unix access to /dev/urandom even when urandom is accessable for some weird reason mib[0] = CTL_KERN; mib[1] = KERN_ARND; sysctl(mib, 2, rnd, &len, NULL, 0); #else fillRandom(rnd,len); #endif arc4_addrandom(rnd, sizeof(rnd)); /* * Discard early keystream, as per recommendations in: * http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Rc4_ksa.ps */ for (i = 0; i < 256; i++) (void)arc4_getbyte(); arc4_count = 1600000; } static void arc4_stir_if_needed(void) { pid_t pid = boost::this_thread::get_id(); if (arc4_count <= 0 || !rs_initialized /*|| arc4_stir_pid != pid*/) { // other threads use the same random generator for us arc4_stir_pid = pid; arc4_stir(); } } static inline u_int8_t arc4_getbyte(void) { u_int8_t si, sj; rs.i = (rs.i + 1); si = rs.s[rs.i]; rs.j = (rs.j + si); sj = rs.s[rs.j]; rs.s[rs.i] = sj; rs.s[rs.j] = si; return (rs.s[(si + sj) & 0xff]); } static inline u_int32_t arc4_getword(void) { u_int32_t val; val = arc4_getbyte() << 24; val |= arc4_getbyte() << 16; val |= arc4_getbyte() << 8; val |= arc4_getbyte(); return val; } void arc4random_stir(void) { arc4_stir(); } void arc4random_addrandom(u_char *dat, int datlen) { if (!rs_initialized) arc4_stir(); arc4_addrandom(dat, datlen); } u_int32_t arc4randomT(void) { u_int32_t val; arc4_count -= 4; arc4_stir_if_needed(); val = arc4_getword(); return val; } void arc4random_buf(void *_buf, size_t n) { u_char *buf = (u_char *)_buf; arc4_stir_if_needed(); while (n--) { if (--arc4_count <= 0) arc4_stir(); buf[n] = arc4_getbyte(); } } /* * Calculate a uniformly distributed random number less than upper_bound * avoiding "modulo bias". * * Uniformity is achieved by generating new random numbers until the one * returned is outside the range [0, 2**32 % upper_bound). This * guarantees the selected random number will be inside * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound) * after reduction modulo upper_bound. */ u_int32_t arc4random_uniformT(u_int32_t upper_bound) { u_int32_t r, min; if (upper_bound < 2) return 0; /* 2**32 % x == (2**32 - x) % x */ min = -upper_bound % upper_bound; /* * This could theoretically loop forever but each retry has * p > 0.5 (worst case, usually far better) of selecting a * number inside the range we need, so it should rarely need * to re-roll. */ for (;;) { r = arc4randomT(); if (r >= min) break; } return r % upper_bound; } static boost::mutex arc4mutex; unsigned int arc4random_uniform(unsigned int upper_bound) { arc4mutex.lock(); unsigned int ret = arc4random_uniformT(upper_bound); arc4mutex.unlock(); return ret; } unsigned int arc4random() { arc4mutex.lock(); unsigned int ret = arc4randomT(); arc4mutex.unlock(); return ret; } |
And here are the convinience methods for it:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | unsigned int arc4random(); unsigned int arc4random_uniform(unsigned int upper_bound); int earc4random() { return arc4random(); } int earc4random(int maxValue) { return arc4random_uniform(maxValue); } int earc4random(int minValue, int maxValue) { return arc4random_uniform(maxValue-minValue) + minValue; } |
So you can use it like:
1 2 3 4 5 | unsigned int random[100]; for(int i = 0 ; i < 100; ++i) { random[i] = earc4random(10,30); } |
Enjoy. (:
See also