<?php
	class Base4 {
		public static function to($string) {
			$base4 = '';
			for ($i = 0, $strlen = strlen($string); $i < $strlen; $i++) {
				$base4 .= base_convert(ord($string[$i]), 10, 4);
			}
			return $base4;
		}
		
		public static function from($base4) {
			$string = '';
			for ($i = 0, $strlen = strlen($base4); $i < $strlen; $i += 4) {
				$string .= chr(base_convert(substr($base4, $i, 4), 4, 10));
			}
			return $string;
		}
	}
	
	$str = 'help';

	$base4 = Base4::to( $str ); 
	var_dump($base4); //string(16) "1220121112301300"
	
	$str = Base4::from( $base4 );
	var_dump($str); 
?>

string(16) "1220121112301300"
string(4) "help"