/*      $NetBSD: arc4random.c,v 1.6 2024/08/18 20:47:20 christos Exp $  */

/* 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 <[email protected]>
* Copyright (c) 2008, Damien Miller <[email protected]>
*
* 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>
#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

/* 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 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));
       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, 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 == getrandom(&buf[len], n, 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));
       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 int
arc4_stir(void)
{
       int     i;

       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();

       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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