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/* 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
#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));
memset(buf, 0, 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));
memset(buf, 0, 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));
memset(buf, 0, 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;
}
memset(entropy, 0, sizeof(entropy));
memset(buf, 0, sizeof(buf));
return 0;
}
#endif
#ifndef WIN32
#define TRY_SEED_URANDOM
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
};
unsigned char buf[ADD_ENTROPY];
int fd, i;
size_t n;
for (i = 0; filenames[i]; ++i) {
fd = evutil_open_closeonexec(filenames[i], O_RDONLY, 0);
if (fd<0)
continue;
n = read_all(fd, buf, sizeof(buf));
close(fd);
if (n != sizeof(buf))
return -1;
arc4_addrandom(buf, sizeof(buf));
memset(buf, 0, sizeof(buf));
arc4_seeded_ok = 1;
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 (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
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