arc4random.c - platform/external/libevent - Gitiles

 /* Portable arc4random.c based on arc4random.c from OpenBSD.
  * Portable version by Chris Davis, adapted for Libevent by Nick Mathewson
  * Copyright (c) 2010 Chris Davis, Niels Provos, and Nick Mathewson
  * Copyright (c) 2010-2012 Niels Provos and Nick Mathewson
  *
  * Note that in Libevent, this file isn't compiled directly.  Instead,
  * it's included from evutil_rand.c
  */

 /*
  * 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.
  *
  * 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.
  */

 #ifndef ARC4RANDOM_EXPORT
 #define ARC4RANDOM_EXPORT
 #endif

 #ifndef ARC4RANDOM_UINT32
 #define ARC4RANDOM_UINT32 uint32_t
 #endif

 #ifndef ARC4RANDOM_NO_INCLUDES
 #include "evconfig-private.h"
 #ifdef _WIN32
 #include <wincrypt.h>
 #include <process.h>
 #else
 #include <fcntl.h>
 #include <unistd.h>
 #include <sys/param.h>
 #include <sys/time.h>
 #ifdef EVENT__HAVE_SYS_SYSCTL_H
 #include <sys/sysctl.h>
 #endif
 #endif
 #include <limits.h>
 #include <stdlib.h>
 #include <string.h>
 #endif

 /* Add platform entropy 32 bytes (256 bits) at a time. */
 #define ADD_ENTROPY 32

 /* Re-seed from the platform RNG after generating this many bytes. */
 #define BYTES_BEFORE_RESEED 1600000

 struct arc4_stream {
 	unsigned char i;
 	unsigned char j;
 	unsigned char s[256];
 };

 #ifdef _WIN32
 #define getpid _getpid
 #define pid_t int
 #endif

 static int rs_initialized;
 static struct arc4_stream rs;
 static pid_t arc4_stir_pid;
 static int arc4_count;
 static int arc4_seeded_ok;

 static inline unsigned char 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(const unsigned char *dat, int datlen)
 {
 	int     n;
 	unsigned char 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;
 }

 #ifndef _WIN32
 static ssize_t
 read_all(int fd, unsigned char *buf, size_t count)
 {
 	size_t numread = 0;
 	ssize_t result;

 	while (numread < count) {
 		result = read(fd, buf+numread, count-numread);
 		if (result<0)
 			return -1;
 		else if (result == 0)
 			break;
 		numread += result;
 	}

 	return (ssize_t)numread;
 }
 #endif

 #ifdef _WIN32
 #define TRY_SEED_WIN32
 static int
 arc4_seed_win32(void)
 {
 	/* This is adapted from Tor's crypto_seed_rng() */
 	static int provider_set = 0;
 	static HCRYPTPROV provider;
 	unsigned char buf[ADD_ENTROPY];

 	if (!provider_set) {
 		if (!CryptAcquireContext(&provider, NULL, NULL, PROV_RSA_FULL,
 		    CRYPT_VERIFYCONTEXT)) {
 			if (GetLastError() != (DWORD)NTE_BAD_KEYSET)
 				return -1;
 		}
 		provider_set = 1;
 	}
 	if (!CryptGenRandom(provider, sizeof(buf), buf))
 		return -1;
 	arc4_addrandom(buf, sizeof(buf));
 	evutil_memclear_(buf, sizeof(buf));
 	arc4_seeded_ok = 1;
 	return 0;
 }
 #endif

 #if defined(EVENT__HAVE_SYS_SYSCTL_H) && defined(EVENT__HAVE_SYSCTL)
 #if EVENT__HAVE_DECL_CTL_KERN && EVENT__HAVE_DECL_KERN_RANDOM && EVENT__HAVE_DECL_RANDOM_UUID
 #define TRY_SEED_SYSCTL_LINUX
 static int
 arc4_seed_sysctl_linux(void)
 {
 	/* Based on code by William Ahern, this function tries to use the
 	 * RANDOM_UUID sysctl to get entropy from the kernel.  This can work
 	 * even if /dev/urandom is inaccessible for some reason (e.g., we're
 	 * running in a chroot). */
 	int mib[] = { CTL_KERN, KERN_RANDOM, RANDOM_UUID };
 	unsigned char buf[ADD_ENTROPY];
 	size_t len, n;
 	unsigned i;
 	int any_set;

 	memset(buf, 0, sizeof(buf));

 	for (len = 0; len < sizeof(buf); len += n) {
 		n = sizeof(buf) - len;

 		if (0 != sysctl(mib, 3, &buf[len], &n, NULL, 0))
 			return -1;
 	}
 	/* make sure that the buffer actually got set. */
 	for (i=0,any_set=0; i<sizeof(buf); ++i) {
 		any_set |= buf[i];
 	}
 	if (!any_set)
 		return -1;

 	arc4_addrandom(buf, sizeof(buf));
 	evutil_memclear_(buf, sizeof(buf));
 	arc4_seeded_ok = 1;
 	return 0;
 }
 #endif

 #if EVENT__HAVE_DECL_CTL_KERN && EVENT__HAVE_DECL_KERN_ARND
 #define TRY_SEED_SYSCTL_BSD
 static int
 arc4_seed_sysctl_bsd(void)
 {
 	/* Based on code from William Ahern and from OpenBSD, this function
 	 * tries to use the KERN_ARND syscall to get entropy from the kernel.
 	 * This can work even if /dev/urandom is inaccessible for some reason
 	 * (e.g., we're running in a chroot). */
 	int mib[] = { CTL_KERN, KERN_ARND };
 	unsigned char buf[ADD_ENTROPY];
 	size_t len, n;
 	int i, any_set;

 	memset(buf, 0, sizeof(buf));

 	len = sizeof(buf);
 	if (sysctl(mib, 2, buf, &len, NULL, 0) == -1) {
 		for (len = 0; len < sizeof(buf); len += sizeof(unsigned)) {
 			n = sizeof(unsigned);
 			if (n + len > sizeof(buf))
 			    n = len - sizeof(buf);
 			if (sysctl(mib, 2, &buf[len], &n, NULL, 0) == -1)
 				return -1;
 		}
 	}
 	/* make sure that the buffer actually got set. */
 	for (i=any_set=0; i<sizeof(buf); ++i) {
 		any_set |= buf[i];
 	}
 	if (!any_set)
 		return -1;

 	arc4_addrandom(buf, sizeof(buf));
 	evutil_memclear_(buf, sizeof(buf));
 	arc4_seeded_ok = 1;
 	return 0;
 }
 #endif
 #endif /* defined(EVENT__HAVE_SYS_SYSCTL_H) */

 #ifdef __linux__
 #define TRY_SEED_PROC_SYS_KERNEL_RANDOM_UUID
 static int
 arc4_seed_proc_sys_kernel_random_uuid(void)
 {
 	/* Occasionally, somebody will make /proc/sys accessible in a chroot,
 	 * but not /dev/urandom.  Let's try /proc/sys/kernel/random/uuid.
 	 * Its format is stupid, so we need to decode it from hex.
 	 */
 	int fd;
 	char buf[128];
 	unsigned char entropy[64];
 	int bytes, n, i, nybbles;
 	for (bytes = 0; bytes<ADD_ENTROPY; ) {
 		fd = evutil_open_closeonexec_("/proc/sys/kernel/random/uuid", O_RDONLY, 0);
 		if (fd < 0)
 			return -1;
 		n = read(fd, buf, sizeof(buf));
 		close(fd);
 		if (n<=0)
 			return -1;
 		memset(entropy, 0, sizeof(entropy));
 		for (i=nybbles=0; i<n; ++i) {
 			if (EVUTIL_ISXDIGIT_(buf[i])) {
 				int nyb = evutil_hex_char_to_int_(buf[i]);
 				if (nybbles & 1) {
 					entropy[nybbles/2] |= nyb;
 				} else {
 					entropy[nybbles/2] |= nyb<<4;
 				}
 				++nybbles;
 			}
 		}
 		if (nybbles < 2)
 			return -1;
 		arc4_addrandom(entropy, nybbles/2);
 		bytes += nybbles/2;
 	}
 	evutil_memclear_(entropy, sizeof(entropy));
 	evutil_memclear_(buf, sizeof(buf));
 	arc4_seeded_ok = 1;
 	return 0;
 }
 #endif

 #ifndef _WIN32
 #define TRY_SEED_URANDOM
 static char *arc4random_urandom_filename = NULL;

 static int arc4_seed_urandom_helper_(const char *fname)
 {
 	unsigned char buf[ADD_ENTROPY];
 	int fd;
 	size_t n;

 	fd = evutil_open_closeonexec_(fname, O_RDONLY, 0);
 	if (fd<0)
 		return -1;
 	n = read_all(fd, buf, sizeof(buf));
 	close(fd);
 	if (n != sizeof(buf))
 		return -1;
 	arc4_addrandom(buf, sizeof(buf));
 	evutil_memclear_(buf, sizeof(buf));
 	arc4_seeded_ok = 1;
 	return 0;
 }

 static int
 arc4_seed_urandom(void)
 {
 	/* This is adapted from Tor's crypto_seed_rng() */
 	static const char *filenames[] = {
 		"/dev/srandom", "/dev/urandom", "/dev/random", NULL
 	};
 	int i;
 	if (arc4random_urandom_filename)
 		return arc4_seed_urandom_helper_(arc4random_urandom_filename);

 	for (i = 0; filenames[i]; ++i) {
 		if (arc4_seed_urandom_helper_(filenames[i]) == 0) {
 			return 0;
 		}
 	}

 	return -1;
 }
 #endif

 static int
 arc4_seed(void)
 {
 	int ok = 0;
 	/* We try every method that might work, and don't give up even if one
 	 * does seem to work.  There's no real harm in over-seeding, and if
 	 * one of these sources turns out to be broken, that would be bad. */
 #ifdef TRY_SEED_WIN32
 	if (0 == arc4_seed_win32())
 		ok = 1;
 #endif
 #ifdef TRY_SEED_URANDOM
 	if (0 == arc4_seed_urandom())
 		ok = 1;
 #endif
 #ifdef TRY_SEED_PROC_SYS_KERNEL_RANDOM_UUID
 	if (arc4random_urandom_filename == NULL &&
 	    0 == arc4_seed_proc_sys_kernel_random_uuid())
 		ok = 1;
 #endif
 #ifdef TRY_SEED_SYSCTL_LINUX
 	/* Apparently Linux is deprecating sysctl, and spewing warning
 	 * messages when you try to use it. */
 	if (!ok && 0 == arc4_seed_sysctl_linux())
 		ok = 1;
 #endif
 #ifdef TRY_SEED_SYSCTL_BSD
 	if (0 == arc4_seed_sysctl_bsd())
 		ok = 1;
 #endif
 	return ok ? 0 : -1;
 }

 static int
 arc4_stir(void)
 {
 	int     i;

 	if (!rs_initialized) {
 		arc4_init();
 		rs_initialized = 1;
 	}

 	arc4_seed();
 	if (!arc4_seeded_ok)
 		return -1;

 	/*
 	 * Discard early keystream, as per recommendations in
 	 * "Weaknesses in the Key Scheduling Algorithm of RC4" by
 	 * Scott Fluhrer, Itsik Mantin, and Adi Shamir.
 	 * http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Rc4_ksa.ps
 	 *
 	 * Ilya Mironov's "(Not So) Random Shuffles of RC4" suggests that
 	 * we drop at least 2*256 bytes, with 12*256 as a conservative
 	 * value.
 	 *
 	 * RFC4345 says to drop 6*256.
 	 *
 	 * At least some versions of this code drop 4*256, in a mistaken
 	 * belief that "words" in the Fluhrer/Mantin/Shamir paper refers
 	 * to processor words.
 	 *
 	 * We add another sect to the cargo cult, and choose 12*256.
 	 */
 	for (i = 0; i < 12*256; i++)
 		(void)arc4_getbyte();

 	arc4_count = BYTES_BEFORE_RESEED;

 	return 0;
 }


 static void
 arc4_stir_if_needed(void)
 {
 	pid_t pid = getpid();

 	if (arc4_count <= 0 || !rs_initialized || arc4_stir_pid != pid)
 	{
 		arc4_stir_pid = pid;
 		arc4_stir();
 	}
 }

 static inline unsigned char
 arc4_getbyte(void)
 {
 	unsigned char 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 unsigned int
 arc4_getword(void)
 {
 	unsigned int val;

 	val = arc4_getbyte() << 24;
 	val |= arc4_getbyte() << 16;
 	val |= arc4_getbyte() << 8;
 	val |= arc4_getbyte();

 	return val;
 }

 #ifndef ARC4RANDOM_NOSTIR
 ARC4RANDOM_EXPORT int
 arc4random_stir(void)
 {
 	int val;
 	ARC4_LOCK_();
 	val = arc4_stir();
 	ARC4_UNLOCK_();
 	return val;
 }
 #endif

 #ifndef ARC4RANDOM_NOADDRANDOM
 ARC4RANDOM_EXPORT void
 arc4random_addrandom(const unsigned char *dat, int datlen)
 {
 	int j;
 	ARC4_LOCK_();
 	if (!rs_initialized)
 		arc4_stir();
 	for (j = 0; j < datlen; j += 256) {
 		/* arc4_addrandom() ignores all but the first 256 bytes of
 		 * its input.  We want to make sure to look at ALL the
 		 * data in 'dat', just in case the user is doing something
 		 * crazy like passing us all the files in /var/log. */
 		arc4_addrandom(dat + j, datlen - j);
 	}
 	ARC4_UNLOCK_();
 }
 #endif

 #ifndef ARC4RANDOM_NORANDOM
 ARC4RANDOM_EXPORT ARC4RANDOM_UINT32
 arc4random(void)
 {
 	ARC4RANDOM_UINT32 val;
 	ARC4_LOCK_();
 	arc4_count -= 4;
 	arc4_stir_if_needed();
 	val = arc4_getword();
 	ARC4_UNLOCK_();
 	return val;
 }
 #endif

 ARC4RANDOM_EXPORT void
 arc4random_buf(void *buf_, size_t n)
 {
 	unsigned char *buf = buf_;
 	ARC4_LOCK_();
 	arc4_stir_if_needed();
 	while (n--) {
 		if (--arc4_count <= 0)
 			arc4_stir();
 		buf[n] = arc4_getbyte();
 	}
 	ARC4_UNLOCK_();
 }

 #ifndef ARC4RANDOM_NOUNIFORM
 /*
  * 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.
  */
 ARC4RANDOM_EXPORT unsigned int
 arc4random_uniform(unsigned int upper_bound)
 {
 	ARC4RANDOM_UINT32 r, min;

 	if (upper_bound < 2)
 		return 0;

 #if (UINT_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;
 }
 #endif
	/* Portable arc4random.c based on arc4random.c from OpenBSD.
	* Portable version by Chris Davis, adapted for Libevent by Nick Mathewson
	* Copyright (c) 2010 Chris Davis, Niels Provos, and Nick Mathewson
	* Copyright (c) 2010-2012 Niels Provos and Nick Mathewson
	*
	* Note that in Libevent, this file isn't compiled directly. Instead,
	* it's included from evutil_rand.c
	*/

	/*
	* 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.
	*
	* 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.
	*/

	#ifndef ARC4RANDOM_EXPORT
	#define ARC4RANDOM_EXPORT
	#endif

	#ifndef ARC4RANDOM_UINT32
	#define ARC4RANDOM_UINT32 uint32_t
	#endif

	#ifndef ARC4RANDOM_NO_INCLUDES
	#include "evconfig-private.h"
	#ifdef _WIN32
	#include <wincrypt.h>
	#include <process.h>
	#else
	#include <fcntl.h>
	#include <unistd.h>
	#include <sys/param.h>
	#include <sys/time.h>
	#ifdef EVENT__HAVE_SYS_SYSCTL_H
	#include <sys/sysctl.h>
	#endif
	#endif
	#include <limits.h>
	#include <stdlib.h>
	#include <string.h>
	#endif

	/* Add platform entropy 32 bytes (256 bits) at a time. */
	#define ADD_ENTROPY 32

	/* Re-seed from the platform RNG after generating this many bytes. */
	#define BYTES_BEFORE_RESEED 1600000

	struct arc4_stream {
	unsigned char i;
	unsigned char j;
	unsigned char s[256];
	};

	#ifdef _WIN32
	#define getpid _getpid
	#define pid_t int
	#endif

	static int rs_initialized;
	static struct arc4_stream rs;
	static pid_t arc4_stir_pid;
	static int arc4_count;
	static int arc4_seeded_ok;

	static inline unsigned char 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(const unsigned char *dat, int datlen)
	{
	int n;
	unsigned char 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;
	}

	#ifndef _WIN32
	static ssize_t
	read_all(int fd, unsigned char *buf, size_t count)
	{
	size_t numread = 0;
	ssize_t result;

	while (numread < count) {
	result = read(fd, buf+numread, count-numread);
	if (result<0)
	return -1;
	else if (result == 0)
	break;
	numread += result;
	}

	return (ssize_t)numread;
	}
	#endif

	#ifdef _WIN32
	#define TRY_SEED_WIN32
	static int
	arc4_seed_win32(void)
	{
	/* This is adapted from Tor's crypto_seed_rng() */
	static int provider_set = 0;
	static HCRYPTPROV provider;
	unsigned char buf[ADD_ENTROPY];

	if (!provider_set) {
	if (!CryptAcquireContext(&provider, NULL, NULL, PROV_RSA_FULL,
	CRYPT_VERIFYCONTEXT)) {
	if (GetLastError() != (DWORD)NTE_BAD_KEYSET)
	return -1;
	}
	provider_set = 1;
	}
	if (!CryptGenRandom(provider, sizeof(buf), buf))
	return -1;
	arc4_addrandom(buf, sizeof(buf));
	evutil_memclear_(buf, sizeof(buf));
	arc4_seeded_ok = 1;
	return 0;
	}
	#endif

	#if defined(EVENT__HAVE_SYS_SYSCTL_H) && defined(EVENT__HAVE_SYSCTL)
	#if EVENT__HAVE_DECL_CTL_KERN && EVENT__HAVE_DECL_KERN_RANDOM && EVENT__HAVE_DECL_RANDOM_UUID
	#define TRY_SEED_SYSCTL_LINUX
	static int
	arc4_seed_sysctl_linux(void)
	{
	/* Based on code by William Ahern, this function tries to use the
	* RANDOM_UUID sysctl to get entropy from the kernel. This can work
	* even if /dev/urandom is inaccessible for some reason (e.g., we're
	* running in a chroot). */
	int mib[] = { CTL_KERN, KERN_RANDOM, RANDOM_UUID };
	unsigned char buf[ADD_ENTROPY];
	size_t len, n;
	unsigned i;
	int any_set;

	memset(buf, 0, sizeof(buf));

	for (len = 0; len < sizeof(buf); len += n) {
	n = sizeof(buf) - len;

	if (0 != sysctl(mib, 3, &buf[len], &n, NULL, 0))
	return -1;
	}
	/* make sure that the buffer actually got set. */
	for (i=0,any_set=0; i<sizeof(buf); ++i) {
	any_set \|= buf[i];
	}
	if (!any_set)
	return -1;

	arc4_addrandom(buf, sizeof(buf));
	evutil_memclear_(buf, sizeof(buf));
	arc4_seeded_ok = 1;
	return 0;
	}
	#endif

	#if EVENT__HAVE_DECL_CTL_KERN && EVENT__HAVE_DECL_KERN_ARND
	#define TRY_SEED_SYSCTL_BSD
	static int
	arc4_seed_sysctl_bsd(void)
	{
	/* Based on code from William Ahern and from OpenBSD, this function
	* tries to use the KERN_ARND syscall to get entropy from the kernel.
	* This can work even if /dev/urandom is inaccessible for some reason
	* (e.g., we're running in a chroot). */
	int mib[] = { CTL_KERN, KERN_ARND };
	unsigned char buf[ADD_ENTROPY];
	size_t len, n;
	int i, any_set;

	memset(buf, 0, sizeof(buf));

	len = sizeof(buf);
	if (sysctl(mib, 2, buf, &len, NULL, 0) == -1) {
	for (len = 0; len < sizeof(buf); len += sizeof(unsigned)) {
	n = sizeof(unsigned);
	if (n + len > sizeof(buf))
	n = len - sizeof(buf);
	if (sysctl(mib, 2, &buf[len], &n, NULL, 0) == -1)
	return -1;
	}
	}
	/* make sure that the buffer actually got set. */
	for (i=any_set=0; i<sizeof(buf); ++i) {
	any_set \|= buf[i];
	}
	if (!any_set)
	return -1;

	arc4_addrandom(buf, sizeof(buf));
	evutil_memclear_(buf, sizeof(buf));
	arc4_seeded_ok = 1;
	return 0;
	}
	#endif
	#endif /* defined(EVENT__HAVE_SYS_SYSCTL_H) */

	#ifdef __linux__
	#define TRY_SEED_PROC_SYS_KERNEL_RANDOM_UUID
	static int
	arc4_seed_proc_sys_kernel_random_uuid(void)
	{
	/* Occasionally, somebody will make /proc/sys accessible in a chroot,
	* but not /dev/urandom. Let's try /proc/sys/kernel/random/uuid.
	* Its format is stupid, so we need to decode it from hex.
	*/
	int fd;
	char buf[128];
	unsigned char entropy[64];
	int bytes, n, i, nybbles;
	for (bytes = 0; bytes<ADD_ENTROPY; ) {
	fd = evutil_open_closeonexec_("/proc/sys/kernel/random/uuid", O_RDONLY, 0);
	if (fd < 0)
	return -1;
	n = read(fd, buf, sizeof(buf));
	close(fd);
	if (n<=0)
	return -1;
	memset(entropy, 0, sizeof(entropy));
	for (i=nybbles=0; i<n; ++i) {
	if (EVUTIL_ISXDIGIT_(buf[i])) {
	int nyb = evutil_hex_char_to_int_(buf[i]);
	if (nybbles & 1) {
	entropy[nybbles/2] \|= nyb;
	} else {
	entropy[nybbles/2] \|= nyb<<4;
	}
	++nybbles;
	}
	}
	if (nybbles < 2)
	return -1;
	arc4_addrandom(entropy, nybbles/2);
	bytes += nybbles/2;
	}
	evutil_memclear_(entropy, sizeof(entropy));
	evutil_memclear_(buf, sizeof(buf));
	arc4_seeded_ok = 1;
	return 0;
	}
	#endif

	#ifndef _WIN32
	#define TRY_SEED_URANDOM
	static char *arc4random_urandom_filename = NULL;

	static int arc4_seed_urandom_helper_(const char *fname)
	{
	unsigned char buf[ADD_ENTROPY];
	int fd;
	size_t n;

	fd = evutil_open_closeonexec_(fname, O_RDONLY, 0);
	if (fd<0)
	return -1;
	n = read_all(fd, buf, sizeof(buf));
	close(fd);
	if (n != sizeof(buf))
	return -1;
	arc4_addrandom(buf, sizeof(buf));
	evutil_memclear_(buf, sizeof(buf));
	arc4_seeded_ok = 1;
	return 0;
	}

	static int
	arc4_seed_urandom(void)
	{
	/* This is adapted from Tor's crypto_seed_rng() */
	static const char *filenames[] = {
	"/dev/srandom", "/dev/urandom", "/dev/random", NULL
	};
	int i;
	if (arc4random_urandom_filename)
	return arc4_seed_urandom_helper_(arc4random_urandom_filename);

	for (i = 0; filenames[i]; ++i) {
	if (arc4_seed_urandom_helper_(filenames[i]) == 0) {
	return 0;
	}
	}

	return -1;
	}
	#endif

	static int
	arc4_seed(void)
	{
	int ok = 0;
	/* We try every method that might work, and don't give up even if one
	* does seem to work. There's no real harm in over-seeding, and if
	* one of these sources turns out to be broken, that would be bad. */
	#ifdef TRY_SEED_WIN32
	if (0 == arc4_seed_win32())
	ok = 1;
	#endif
	#ifdef TRY_SEED_URANDOM
	if (0 == arc4_seed_urandom())
	ok = 1;
	#endif
	#ifdef TRY_SEED_PROC_SYS_KERNEL_RANDOM_UUID
	if (arc4random_urandom_filename == NULL &&
	0 == arc4_seed_proc_sys_kernel_random_uuid())
	ok = 1;
	#endif
	#ifdef TRY_SEED_SYSCTL_LINUX
	/* Apparently Linux is deprecating sysctl, and spewing warning
	* messages when you try to use it. */
	if (!ok && 0 == arc4_seed_sysctl_linux())
	ok = 1;
	#endif
	#ifdef TRY_SEED_SYSCTL_BSD
	if (0 == arc4_seed_sysctl_bsd())
	ok = 1;
	#endif
	return ok ? 0 : -1;
	}

	static int
	arc4_stir(void)
	{
	int i;

	if (!rs_initialized) {
	arc4_init();
	rs_initialized = 1;
	}

	arc4_seed();
	if (!arc4_seeded_ok)
	return -1;

	/*
	* Discard early keystream, as per recommendations in
	* "Weaknesses in the Key Scheduling Algorithm of RC4" by
	* Scott Fluhrer, Itsik Mantin, and Adi Shamir.
	* http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Rc4_ksa.ps
	*
	* Ilya Mironov's "(Not So) Random Shuffles of RC4" suggests that
	* we drop at least 2256 bytes, with 12256 as a conservative
	* value.
	*
	* RFC4345 says to drop 6*256.
	*
	* At least some versions of this code drop 4*256, in a mistaken
	* belief that "words" in the Fluhrer/Mantin/Shamir paper refers
	* to processor words.
	*
	* We add another sect to the cargo cult, and choose 12*256.
	*/
	for (i = 0; i < 12*256; i++)
	(void)arc4_getbyte();

	arc4_count = BYTES_BEFORE_RESEED;

	return 0;
	}


	static void
	arc4_stir_if_needed(void)
	{
	pid_t pid = getpid();

	if (arc4_count <= 0 \|\| !rs_initialized \|\| arc4_stir_pid != pid)
	{
	arc4_stir_pid = pid;
	arc4_stir();
	}
	}

	static inline unsigned char
	arc4_getbyte(void)
	{
	unsigned char 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 unsigned int
	arc4_getword(void)
	{
	unsigned int val;

	val = arc4_getbyte() << 24;
	val \|= arc4_getbyte() << 16;
	val \|= arc4_getbyte() << 8;
	val \|= arc4_getbyte();

	return val;
	}

	#ifndef ARC4RANDOM_NOSTIR
	ARC4RANDOM_EXPORT int
	arc4random_stir(void)
	{
	int val;
	ARC4_LOCK_();
	val = arc4_stir();
	ARC4_UNLOCK_();
	return val;
	}
	#endif

	#ifndef ARC4RANDOM_NOADDRANDOM
	ARC4RANDOM_EXPORT void
	arc4random_addrandom(const unsigned char *dat, int datlen)
	{
	int j;
	ARC4_LOCK_();
	if (!rs_initialized)
	arc4_stir();
	for (j = 0; j < datlen; j += 256) {
	/* arc4_addrandom() ignores all but the first 256 bytes of
	* its input. We want to make sure to look at ALL the
	* data in 'dat', just in case the user is doing something
	* crazy like passing us all the files in /var/log. */
	arc4_addrandom(dat + j, datlen - j);
	}
	ARC4_UNLOCK_();
	}
	#endif

	#ifndef ARC4RANDOM_NORANDOM
	ARC4RANDOM_EXPORT ARC4RANDOM_UINT32
	arc4random(void)
	{
	ARC4RANDOM_UINT32 val;
	ARC4_LOCK_();
	arc4_count -= 4;
	arc4_stir_if_needed();
	val = arc4_getword();
	ARC4_UNLOCK_();
	return val;
	}
	#endif

	ARC4RANDOM_EXPORT void
	arc4random_buf(void *buf_, size_t n)
	{
	unsigned char *buf = buf_;
	ARC4_LOCK_();
	arc4_stir_if_needed();
	while (n--) {
	if (--arc4_count <= 0)
	arc4_stir();
	buf[n] = arc4_getbyte();
	}
	ARC4_UNLOCK_();
	}

	#ifndef ARC4RANDOM_NOUNIFORM
	/*
	* 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
	* [232 % upper_bound, 232) which maps back to [0, upper_bound)
	* after reduction modulo upper_bound.
	*/
	ARC4RANDOM_EXPORT unsigned int
	arc4random_uniform(unsigned int upper_bound)
	{
	ARC4RANDOM_UINT32 r, min;

	if (upper_bound < 2)
	return 0;

	#if (UINT_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 == 232 % x when x <= 231 */
	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;
	}
	#endif