/* * 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 __FBSDID("$FreeBSD$"); #include #include #include #include #include #include struct arc4_stream { u_int8_t i; u_int8_t j; u_int8_t s[256]; }; #define RANDOMDEV "/dev/urandom" #define KEYSIZE 128 #ifdef __REENTRANT static pthread_mutex_t arc4random_mtx = PTHREAD_MUTEX_INITIALIZER; #define THREAD_LOCK() pthread_mutex_lock(&arc4random_mtx) #define THREAD_UNLOCK() pthread_mutex_unlock(&arc4random_mtx) #else #define THREAD_LOCK() #define THREAD_UNLOCK() #endif static struct arc4_stream rs; 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); 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 void arc4_stir(void) { int done, fd, n; struct { struct timeval tv; pid_t pid; u_int8_t rnd[KEYSIZE]; } rdat; fd = open(RANDOMDEV, O_RDONLY, 0); done = 0; if (fd >= 0) { if (read(fd, &rdat, KEYSIZE) == KEYSIZE) done = 1; (void)close(fd); } if (!done) { (void)gettimeofday(&rdat.tv, NULL); rdat.pid = getpid(); /* We'll just take whatever was on the stack too... */ } 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; } 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); } static void arc4_check_init(void) { if (!rs_initialized) { arc4_init(); rs_initialized = 1; } } static inline void arc4_check_stir(void) { if (!rs_stired || arc4_count <= 0) { arc4_stir(); rs_stired = 1; } } void arc4random_stir(void) { THREAD_LOCK(); arc4_check_init(); arc4_stir(); rs_stired = 1; THREAD_UNLOCK(); } void arc4random_addrandom(u_char *dat, int datlen) { THREAD_LOCK(); arc4_check_init(); arc4_check_stir(); arc4_addrandom(dat, datlen); THREAD_UNLOCK(); } u_int32_t arc4random(void) { u_int32_t rnd; THREAD_LOCK(); arc4_check_init(); arc4_check_stir(); rnd = arc4_getword(); arc4_count -= 4; THREAD_UNLOCK(); return (rnd); } void arc4random_buf(void *_buf, size_t n) { u_char *buf = (u_char *)_buf; THREAD_LOCK(); arc4_check_init(); while (n--) { arc4_check_stir(); buf[n] = arc4_getbyte(); arc4_count--; } THREAD_UNLOCK(); } /* * 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 /*-------- 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