public static function getBinary($length = 32)
{
if ($length < 1) {
return '';
}
// There's not much point reading more than 256 bits of entropy from any single source.
$capped_length = min($length, 32);
// As usual, Windows requires special consideration.
$is_windows = strtoupper(substr(PHP_OS, 0, 3)) === 'WIN';
// Variables to store state during entropy collection.
$entropy = array();
$sources = array();
$total_strength = 0;
$required_strength = 5;
// Try getting entropy from various sources that are known to be good.
if (function_exists('openssl_random_pseudo_bytes') && (!$is_windows || version_compare(PHP_VERSION, '5.4', '>='))) {
$entropy[] = openssl_random_pseudo_bytes($capped_length, $crypto_strong);
$sources[] = 'openssl';
$total_strength += $crypto_strong ? 3 : 1;
} elseif (function_exists('mcrypt_create_iv') && (!$is_windows || version_compare(PHP_VERSION, '5.3.7', '>='))) {
$entropy[] = mcrypt_create_iv($capped_length, MCRYPT_DEV_URANDOM);
$sources[] = 'mcrypt_dev_urandom';
$total_strength += 4;
} elseif ($is_windows && function_exists('mcrypt_create_iv') && defined('MCRYPT_RAND')) {
$entropy[] = mcrypt_create_iv($capped_length, MCRYPT_RAND);
$sources[] = 'mcrypt_rand';
$total_strength += 2;
} elseif (!$is_windows && file_exists('/dev/urandom') && is_readable('/dev/urandom')) {
$entropy[] = fread($fp = fopen('/dev/urandom', 'rb'), $capped_length);
fclose($fp);
$sources[] = 'dev_urandom';
$total_strength += 4;
}
// Supplement with multiple calls to rand() and mt_rand().
while ($total_strength < $required_strength) {
$rand = '';
for ($i = 0; $i < $capped_length; $i += 4) {
$rand .= pack('L', rand(0, 0x7fffffff) ^ mt_rand(0, 0x7fffffff));
}
$entropy[] = $rand;
$sources[] = 'mt_rand';
$total_strength += 1;
}
// Mix the entropy sources together using SHA-512.
$mixer_content = end($entropy);
$mixer_output = '';
if (function_exists('hash_hmac') && in_array('sha256', hash_algos())) {
for ($i = 0; $i < $length; $i += 32) {
foreach ($entropy as $item) {
$mixer_content = hash_hmac('sha256', $item, $mixer_content . $i, true);
}
$mixer_output .= $mixer_content;
}
} else {
for ($i = 0; $i < $length; $i += 20) {
foreach ($entropy as $item) {
$mixer_content = sha1($item . $mixer_content . $i . microtime(), true);
}
$mixer_output .= $mixer_content;
}
}
self::$_sources = $sources;
return substr($mixer_output, 0, $length);
}
