/*

 * random.c

 *    Acquire randomness from system, for seeding RNG.

 *    Get pseudo random numbers from RNG.

 *

 * Copyright (c) 2001 Marko Kreen

 * Copyright (c) 2019 Henning Westerholt

 * All rights reserved.

 *

 * Based on https://github.com/waitman/libfortuna, refactoring

 * done in this version: https://github.com/henningw/libfortuna

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 * 1. Redistributions of source code must retain the above copyright

 *    notice, this list of conditions and the following disclaimer.

 * 2. Redistributions in binary form must reproduce the above copyright

 *    notice, this list of conditions and the following disclaimer in the

 *    documentation and/or other materials provided with the distribution.

 *

 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND

 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE

 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE

 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL

 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS

 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)

 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT

 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY

 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF

 * SUCH DAMAGE.

 *

 * contrib/pgcrypto/random.c

 */

#include <errno.h>

#include <time.h>

#include <sys/types.h>

#include <string.h>

#include "../../dprint.h"

#include "random.h"

#include "fortuna.h"

/* how many bytes to ask from system random provider */

#define RND_BYTES 32

/*

 * Try to read from /dev/urandom or /dev/random on these OS'es.

 *

 * The list can be pretty liberal, as the device not existing

 * is expected event.

 */

#include <fcntl.h>

#include <unistd.h>

static time_t seed_time = 0;

static time_t check_time = 0;

int sr_get_pseudo_random_bytes(u_int8_t *dst, unsigned count);

/* private functions */

static int safe_read(int fd, void *buf, size_t count)

{

  int done = 0;

  char *p = buf;

  int res;

  while(count) {

    res = read(fd, p, count);

    if(res <= 0) {

      if(errno == EINTR)

        continue;

      return -10;

    }

    p += res;

    done += res;

    count -= res;

  }

  return done;

}

static u_int8_t *try_dev_random(u_int8_t *dst)

{

  int fd;

  int res;

  fd = open("/dev/urandom", O_RDONLY, 0);

  if(fd == -1) {

    fd = open("/dev/random", O_RDONLY, 0);

    if(fd == -1)

      return dst;

  }

  res = safe_read(fd, dst, RND_BYTES);

  close(fd);

  if(res > 0)

    dst += res;

  return dst;

}

/*

 * try to extract some randomness for initial seeding

 *

 * dst should have room for 1024 bytes.

 */

static unsigned acquire_system_randomness(u_int8_t *dst)

{

  u_int8_t *p = dst;

  p = try_dev_random(p);

  return p - dst;

}

static void system_reseed(void)

{

  u_int8_t buf[1024];

  int n;

  time_t t;

  int skip = 1;

  t = time(NULL);

  if(seed_time == 0)

    skip = 0;

  else if((t - seed_time) < SYSTEM_RESEED_MIN)

    skip = 1;

  else if((t - seed_time) > SYSTEM_RESEED_MAX)

    skip = 0;

  else if(check_time == 0 || (t - check_time) > SYSTEM_RESEED_CHECK_TIME) {

    check_time = t;

    /* roll dice */

    sr_get_pseudo_random_bytes(buf, 1);

    skip = buf[0] >= SYSTEM_RESEED_CHANCE;

  }

  /* clear 1 byte */

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

  if(skip)

    return;

  n = acquire_system_randomness(buf);

  if(n > 0) {

    fortuna_add_entropy(buf, n);

    LM_DBG("cryptographic PRNG reseed done with %u bytes\n", n);

  }

  seed_time = t;

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

}

/* public functions */

int sr_get_pseudo_random_bytes(u_int8_t *dst, unsigned count)

{

  system_reseed();

  fortuna_get_bytes(count, dst);

  return 0;

}

int sr_add_entropy(const u_int8_t *data, unsigned count)

{

  system_reseed();

  LM_DBG("additional %u bytes entropy added to cryptographic PRNG\n", count);

  fortuna_add_entropy(data, count);

  return 0;

}