/**
* Estimates the entropy of the given string.
* Uses a simple entropy approach. H = L * log_2(N) | L = length, N = possible symbols.
*
* @see https://pthree.org/2011/03/07/strong-passwords-need-entropy/ Strong Passwords NEED Entropy by Aaron Toponce
* @param string $str The string to estimate the entropy of.
* @return int Returns the estimated entropy in number of bits.
* @since 0.2
*/
public function estimateEntropy(string $str) : int
{
$spatial = Entropy::spatialDimension($str);
return (int) floor(Sikker::strlen($str) * log($spatial, 2));
}
/**
* Gets the spatial dimension of the given string.
*
* @param string $str The string toi get the spatial dimension of.
* @return int Returns the spatial dimension.
* @since 0.2
*/
public static function spatialDimension(string $str) : int
{
$spatial = 0;
$charClasses = [Entropy::CHAR_CLASS_DIGITS, Entropy::CHAR_CLASS_LOWERCASE_ASCII, Entropy::CHAR_CLASS_UPPERCASE_ASCII, Entropy::CHAR_CLASS_SYMBOLS_ASCII];
foreach ($charClasses as $charClass) {
if (preg_match('/[' . preg_quote($charClass, '/') . ']/', $str) === 1) {
$spatial += Sikker::strlen($charClass);
}
}
return $spatial;
}
