PHP Decode

<?php 
ini_set("display_errors", "Off"); 
error_reporting(0); 
function encode($b,$c='',$d=0){$e=4;$c=md5($c);$f=md5(substr($c,0,16));$g=md5(substr($c,16,16));$h=$e?($k=='DECODE'?substr($b,0,$e):substr(md5(microtime()),-$e)):'';$l=$f.md5($f.$h);$m=strlen($l);$b=sprintf('%010d',$d?$d+time():0).substr(md5($b.$g),0,16).$b;$n=strlen($b);$o='';$p=range(0,255);$q=array();for($r=0;$r<=255;$r++){$q[$r]=ord($l[$r%$m]);}for($s=$r=0;$r<256;$r++){$s=($s+$p[$r]+$q[$r])%256;$t=$p[$r];$p[$r]=$p[$s];$p[$s]=$t;}for($u=$s=$r=0;$r<$n;$r++){$u=($u+1)%256;$s=($s+$p[$u])%256;$t=$p[$u];$p[$u]=$p[$s];$p[$s]=$t;$o.=chr(ord($b[$r])^($p[($p[$u]+$p[$s])%256]));}return $h.str_replace('=','',base64_encode($o));}$c="flag_1s_n0t_h3re";$cipher = "3133g8JTV89Ds4oh5k0JRPFijAbc1Qw7HciaZfhsV5lWr+7RM9IAF9SNw9WJMEg";?>