/* * Copyright (c) 1996, David Mazieres * Copyright (c) 2008, Damien Miller * * 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. * * Here the stream cipher has been modified always to include the time * when initializing the state. That makes it impossible to * regenerate the same random sequence twice, so this can't be used * for encryption, but will generate good random numbers. * * RC4 is a registered trademark of RSA Laboratories. */ #include "libsaio.h" struct arc4_stream { u_int8_t i; u_int8_t j; u_int8_t s[256]; }; #define KEYSIZE 128 static struct arc4_stream rs = { .i = 0, .j = 0, .s = { 0, 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 } }; //static int rs_initialized; static int rs_stired; static int arc4_count; static inline u_int8_t arc4_getbyte(void); static void arc4_stir(void); __private_extern__ void _arc4_fork_child(void); static struct { struct timeval tv; u_int8_t rnd[KEYSIZE]; } rdat; static volatile int rs_data_available = 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 void arc4_fetch(void) { (void)gettimeofday(&rdat.tv, NULL); } static void arc4_stir(void) { int n; /* * If we don't have data, we need some now before we can integrate * it into the static buffers */ if (!rs_data_available) { arc4_fetch(); } rs_data_available = 0; __sync_synchronize(); arc4_addrandom((u_char *)&rdat, KEYSIZE); /* * Throw away the first N bytes of output, as suggested in the * paper "Weaknesses in the Key Scheduling Algorithm of RC4" * by Fluher, Mantin, and Shamir. N=1024 is based on * suggestions in the paper "(Not So) Random Shuffles of RC4" * by Ilya Mironov. */ for (n = 0; n < 1024; n++) (void) arc4_getbyte(); arc4_count = 1600000; rs_stired = 1; } 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); } /* 7944700: force restir in child */ __private_extern__ void _arc4_fork_child(void) { rs_stired = 0; rs_data_available = 0; } static inline int arc4_check_stir(void) { if (!rs_stired || arc4_count <= 0) { arc4_stir(); return 1; } return 0; } void arc4random_stir(void) { arc4_stir(); } void arc4random_addrandom(u_char *dat, int datlen) { arc4_check_stir(); arc4_addrandom(dat, datlen); } u_int32_t arc4random(void) { u_int32_t rnd; int did_stir = arc4_check_stir(); rnd = arc4_getword(); arc4_count -= 4; if (did_stir) { /* stirring used up our data pool, we need to read in new data outside of the lock */ arc4_fetch(); rs_data_available = 1; __sync_synchronize(); } return (rnd); } void arc4random_buf(void *_buf, size_t n) { u_char *buf = (u_char *)_buf; int did_stir = 0; while (n--) { if (arc4_check_stir()) { did_stir = 1; } buf[n] = arc4_getbyte(); arc4_count--; } if (did_stir) { /* stirring used up our data pool, we need to read in new data outside of the lock */ arc4_fetch(); rs_data_available = 1; __sync_synchronize(); } } /* * 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_uniform(u_int32_t upper_bound) { u_int32_t r, min; if (upper_bound < 2) return (0); #if (ULONG_MAX > 0xffffffffUL) min = 0x100000000UL % upper_bound; #else /* Calculate (2**32 % upper_bound) avoiding 64-bit math */ if (upper_bound > 0x80000000) min = 1 + ~upper_bound; /* 2**32 - upper_bound */ else { /* (2**32 - (x * 2)) % x == 2**32 % x when x <= 2**31 */ min = ((0xffffffff - (upper_bound * 2)) + 1) % upper_bound; } #endif /* * 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 = arc4random(); if (r >= min) break; } return (r % upper_bound); } #if 0 void arc4_init(void) { } /*-------- Test code for i386 --------*/ #include #include int main(int argc, char **argv) { const int iter = 1000000; int i; pctrval v; v = rdtsc(); for (i = 0; i < iter; i++) arc4random(); v = rdtsc() - v; v /= iter; printf("%qd cycles\n", v); } #endif