/*  $OpenBSD: arc4random.c,v 1.58 2022/07/31 13:41:45 tb Exp $  */

/*

 * Copyright (c) 1996, David Mazieres <dm@uun.org>

 * Copyright (c) 2008, Damien Miller <djm@openbsd.org>

 * Copyright (c) 2013, Markus Friedl <markus@openbsd.org>

 * Copyright (c) 2014, Theo de Raadt <deraadt@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.

 */

/*

 * ChaCha based random number generator for OpenBSD.

 */

#include <fcntl.h>

#include <limits.h>

#include <signal.h>

#include <stdint.h>

#include <stdlib.h>

#include <string.h>

#include <unistd.h>

#include <sys/types.h>

#include <sys/time.h>

#define KEYSTREAM_ONLY

#include "chacha_private.h"

#define minimum(a, b) ((a) < (b) ? (a) : (b))

#if defined(__GNUC__) || defined(_MSC_VER)

#define inline __inline

#else       /* __GNUC__ || _MSC_VER */

#define inline

#endif        /* !__GNUC__ && !_MSC_VER */

#define KEYSZ 32

#define IVSZ  8

#define BLOCKSZ 64

#define RSBUFSZ (16*BLOCKSZ)

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

/* Marked MAP_INHERIT_ZERO, so zero'd out in fork children. */

static struct _rs {

  size_t    rs_have;  /* valid bytes at end of rs_buf */

  size_t    rs_count; /* bytes till reseed */

} *rs;

/* Maybe be preserved in fork children, if _rs_allocate() decides. */

static struct _rsx {

  chacha_ctx  rs_chacha;  /* chacha context for random keystream */

  u_char    rs_buf[RSBUFSZ];  /* keystream blocks */

} *rsx;

static inline int _rs_allocate(struct _rs **, struct _rsx **);

static inline void _rs_forkdetect(void);

#include "arc4random.h"

static inline void _rs_rekey(u_char *dat, size_t datlen);

static inline void

_rs_init(u_char *buf, size_t n)

{

  if (n < KEYSZ + IVSZ)

    return;

  if (rs == NULL) {

    if (_rs_allocate(&rs, &rsx) == -1)

      _exit(1);

  }

  chacha_keysetup(&rsx->rs_chacha, buf, KEYSZ * 8);

  chacha_ivsetup(&rsx->rs_chacha, buf + KEYSZ);

}

static void

_rs_stir(void)

{

  u_char rnd[KEYSZ + IVSZ];

  uint32_t rekey_fuzz = 0;

  if (getentropy(rnd, sizeof rnd) == -1)

    _getentropy_fail();

  if (!rs)

    _rs_init(rnd, sizeof(rnd));

  else

    _rs_rekey(rnd, sizeof(rnd));

  explicit_bzero(rnd, sizeof(rnd)); /* discard source seed */

  /* invalidate rs_buf */

  rs->rs_have = 0;

  memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));

  /* rekey interval should not be predictable */

  chacha_encrypt_bytes(&rsx->rs_chacha, (uint8_t *)&rekey_fuzz,

      (uint8_t *)&rekey_fuzz, sizeof(rekey_fuzz));

  rs->rs_count = REKEY_BASE + (rekey_fuzz % REKEY_BASE);

}

static inline void

_rs_stir_if_needed(size_t len)

{

  _rs_forkdetect();

  if (!rs || rs->rs_count <= len)

    _rs_stir();

  if (rs->rs_count <= len)

    rs->rs_count = 0;

  else

    rs->rs_count -= len;

}

static inline void

_rs_rekey(u_char *dat, size_t datlen)

{

#ifndef KEYSTREAM_ONLY

  memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));

#endif

  /* fill rs_buf with the keystream */

  chacha_encrypt_bytes(&rsx->rs_chacha, rsx->rs_buf,

      rsx->rs_buf, sizeof(rsx->rs_buf));

  /* mix in optional user provided data */

  if (dat) {

    size_t i, m;

    m = minimum(datlen, KEYSZ + IVSZ);

    for (i = 0; i < m; i++)

      rsx->rs_buf[i] ^= dat[i];

  }

  /* immediately reinit for backtracking resistance */

  _rs_init(rsx->rs_buf, KEYSZ + IVSZ);

  memset(rsx->rs_buf, 0, KEYSZ + IVSZ);

  rs->rs_have = sizeof(rsx->rs_buf) - KEYSZ - IVSZ;

}

static inline void

_rs_random_buf(void *_buf, size_t n)

{

  u_char *buf = (u_char *)_buf;

  u_char *keystream;

  size_t m;

  _rs_stir_if_needed(n);

  while (n > 0) {

    if (rs->rs_have > 0) {

      m = minimum(n, rs->rs_have);

      keystream = rsx->rs_buf + sizeof(rsx->rs_buf)

          - rs->rs_have;

      memcpy(buf, keystream, m);

      memset(keystream, 0, m);

      buf += m;

      n -= m;

      rs->rs_have -= m;

    }

    if (rs->rs_have == 0)

      _rs_rekey(NULL, 0);

  }

}

static inline void

_rs_random_u32(uint32_t *val)

{

  u_char *keystream;

  _rs_stir_if_needed(sizeof(*val));

  if (rs->rs_have < sizeof(*val))

    _rs_rekey(NULL, 0);

  keystream = rsx->rs_buf + sizeof(rsx->rs_buf) - rs->rs_have;

  memcpy(val, keystream, sizeof(*val));

  memset(keystream, 0, sizeof(*val));

  rs->rs_have -= sizeof(*val);

}

uint32_t

arc4random(void)

{

  uint32_t val;

  _ARC4_LOCK();

  _rs_random_u32(&val);

  _ARC4_UNLOCK();

  return val;

}

void

arc4random_buf(void *buf, size_t n)

{

  _ARC4_LOCK();

  _rs_random_buf(buf, n);

  _ARC4_UNLOCK();

}