某资金盘程序的密码解密脚本

<?php
header("Content-type: text/html; charset=gbk");

?>
<form action="post.php" method="post">
<input type="text" name="content" value="">
<input type="submit" value="提交">
</form>
<?php
//$a=authcode($_POST[‘content‘], "DECODE");
$a=$_POST[‘content‘];
$a=authcode($a, "DECODE");
echo $a;

function authcode($string, $operation = "ENCODE", $key = "", $expiry = 0) {
    $ckey_length = 4;
    $key = md5($key ? $key : "default_key");
    $keya = md5(substr($key, 0, 16));
    $keyb = md5(substr($key, 16, 16));
    $keyc = ($ckey_length ? ($operation == "DECODE" ? substr($string, 0, $ckey_length) : substr(md5(microtime()), -$ckey_length)) : "");
    $cryptkey = $keya . md5($keya . $keyc);
    $key_length = strlen($cryptkey);
    $string = ($operation == "DECODE" ? base64_decode(substr($string, $ckey_length)) : sprintf("%010d", $expiry ? $expiry + time() : 0) . substr(md5($string . $keyb), 0, 16) . $string);
    $string_length = strlen($string);
    $result = "";
    $box = range(0, 255);
    $rndkey = array();

    for ($i = 0; $i <= 255; $i++) {
        $rndkey[$i] = ord($cryptkey[$i % $key_length]);
    }

    for ($j = $i = 0; $i < 256; $i++) {
        $j = ($j + $box[$i] + $rndkey[$i]) % 256;
        $tmp = $box[$i];
        $box[$i] = $box[$j];
        $box[$j] = $tmp;
    }

    for ($a = $j = $i = 0; $i < $string_length; $i++) {
        $a = ($a + 1) % 256;
        $j = ($j + $box[$a]) % 256;
        $tmp = $box[$a];
        $box[$a] = $box[$j];
        $box[$j] = $tmp;
        $result .= chr(ord($string[$i]) ^ $box[($box[$a] + $box[$j]) % 256]);
    }

    if ($operation == "DECODE") {
        if (((substr($result, 0, 10) == 0) || (0 < (substr($result, 0, 10) - time()))) && (substr($result, 10, 16) == substr(md5(substr($result, 26) . $keyb), 0, 16))) {
            return substr($result, 26);
        }
        else {
            return "";
        }
    }
    else {
        return $keyc . str_replace("=", "", base64_encode($result));
    }
}
?>

某次搞定一传销资金盘程序，看了算法，解密如上。