Youtube - Decrypt cipher signature

youtube_decrypt_cipher.php

<?php
// 2017-02-28
function decrypt_signature($s){
	$nF = function(&$a, $b){
		$c = $a[0];
		$a[0] = $a[$b % count($a)];
		$a[$b] = $c;
	};
	$fj = function(&$a, $b){
		array_splice($a, 0, $b);
	};
	$c0 = function(&$a){
		$a = array_reverse($a);
	};

	$a = str_split($s);
	$c0($a, 46);
	$fj($a, 3);
	$nF($a, 53);
	$fj($a, 1);
	$c0($a, 42);
	$nF($a, 25);
	$c0($a, 58);
	return join('', $a);
}