简单有key的加密解密算法

define('KEY', '123456');
$data = 'oehpetyFTdYwZ3frZi1KkgtizgQs';        // 被加密信息  
$encrypt = encrypt($data);  
$decrypt = decrypt($encrypt);  
echo $encrypt, "\n", $decrypt;  
function decrypt($data) {
    $key = md5(KEY);
    $x = 0;
    $data = base64_decode($data);
    $len = strlen($data);
    $l = strlen($key);
    $char = $str = '';
    for ($i = 0; $i < $len; $i++) {
        if ($x == $l) {
            $x = 0;
        }
        $char .= substr($key, $x, 1);
        $x++;
    }
    for ($i = 0; $i < $len; $i++) {
        if (ord(substr($data, $i, 1)) < ord(substr($char, $i, 1))) {
            $str .= chr((ord(substr($data, $i, 1)) + 256) - ord(substr($char, $i, 1)));
        } else {
            $str .= chr(ord(substr($data, $i, 1)) - ord(substr($char, $i, 1)));
        }
    }
    return $str;
}

function encrypt($data) {
    $key = md5(KEY);
    $x = 0;
    $len = strlen($data);
    $l = strlen($key);
    $char = $str = '';
    for ($i = 0; $i < $len; $i++) {
        if ($x == $l) {
            $x = 0;
        }
        $char .= $key{$x};
        $x++;
    }
    for ($i = 0; $i < $len; $i++) {
        $str .= chr(ord($data{$i}) + (ord($char{$i})) % 256);
    }
    return base64_encode($str);
}