/* 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 <bcrypt.h>

#include <process.h>

#include <winerror.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

#ifdef EVENT__HAVE_SYS_RANDOM_H

#include <sys/random.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

#define REKEY_BASE (1024*1024) /* NB. should be a power of 2 */

struct arc4_stream {

  unsigned char i;

  unsigned char j;

  unsigned char s[256];

};

#ifdef _WIN32

#define getpid _getpid

#define pid_t int

#endif

#ifndef O_RDONLY

#define O_RDONLY _O_RDONLY

#endif

static int rs_initialized;

static struct arc4_stream rs;

static pid_t arc4_stir_pid;

static int arc4_count;

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)

{

  unsigned char buf[ADD_ENTROPY];

  if (BCryptGenRandom(NULL, buf, sizeof(buf),

    BCRYPT_USE_SYSTEM_PREFERRED_RNG))

    return -1;

  arc4_addrandom(buf, sizeof(buf));

  evutil_memclear_(buf, sizeof(buf));

  return 0;

}

#endif

#if defined(EVENT__HAVE_GETRANDOM)

#define TRY_SEED_GETRANDOM

static int

arc4_seed_getrandom(void)

{

  unsigned char buf[ADD_ENTROPY];

  size_t len;

  ssize_t n = 0;

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

    n = getrandom(&buf[len], sizeof(buf) - len, 0);

    if (n < 0)

      return -1;

  }

  arc4_addrandom(buf, sizeof(buf));

  evutil_memclear_(buf, sizeof(buf));

  return 0;

}

#endif /* EVENT__HAVE_GETRANDOM */

#if defined(EVENT__HAVE_SYS_SYSCTL_H) && defined(EVENT__HAVE_SYSCTL)

#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));

  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));

  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));

  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_GETRANDOM

  if (0 == arc4_seed_getrandom())

    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_BSD

  if (0 == arc4_seed_sysctl_bsd())

    ok = 1;

#endif

  return ok ? 0 : -1;

}

static inline unsigned int

arc4_getword(void);

static int

arc4_stir(void)

{

  int     i;

  ARC4RANDOM_UINT32 rekey_fuzz; 

  if (!rs_initialized) {

    arc4_init();

    rs_initialized = 1;

  }

  if (0 != arc4_seed())

    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();

  rekey_fuzz = arc4_getword();

  /* rekey interval should not be predictable */

  arc4_count = REKEY_BASE + (rekey_fuzz % REKEY_BASE);

  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 = (unsigned)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

#ifndef EVENT__HAVE_ARC4RANDOM_BUF

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_();

}

#endif  /* #ifndef EVENT__HAVE_ARC4RANDOM_BUF */

#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;

  /* 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 = arc4random();

    if (r >= min)

      break;

  }

  return r % upper_bound;

}

#endif