Two-way Number Hashing

Pair of functions for two-way number hashing. Not secure in any way, just obscures the number for appearances and to discourage people from experimenting with query arguments and URLs (for the kind of person, like me, who tries ?id=1, ?id=2).

Test

Source code

Encoder and decoder functions. Change $key = 'etc' to alter the encoding, but make sure it matches in both.

// Number encoder (1 -> '41259616' | 2 -> '92519226').
function num_encode($in)
{
	if (is_numeric($in) && $in > 0)
	{
		$key = '0495861273';

		for($i=0; $i < strlen($in); $i++) $out .= $key[substr($in, $i, 1)]; // Encode string according to key.

		if (strlen($out) < 7)
		{
			$padding = (7 - strlen($out));
			$out .= substr(($in * 125961), 0, $padding); // Add padding characters.
			$out .= $padding; // Add number of padding characters.
		}
		else $out .= '0'; // No padding characters.

		return $out;
	}
	return false;
}

// Equivalent decoder function ('41259616' -> 1 | '92519226' -> 2).
function num_decode($in)
{
	if (is_numeric($in) && $in > 0)
	{
		$padding = substr($in, -1);

		if ($padding > 0) $in = substr($in, 0, 0 - (1 + $padding)); // Remove padding characters.
		else $in = substr($in, 0, -1); // Remove the padding.

		$key = '0495861273';
		for($i=0; $i<strlen($in); $i++) $out .= strpos($key, $in[$i]); // Decode string according to key.

		return $out;
	}
	return false;
}