public function getRandomKey($length = 20)
{
$chars = "A1B2C3D4E5F6G7H8I9J0K1L2M3N4O5P6Q7R8S9T0U1V2W3X4Y5Z6a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6q7r8s9t0u1v2w3x4y5z6";
$key = "";
for ($i = 0; $i < $length; $i++) {
$key .= $chars[mt_rand(0, strlen($chars) - 1)];
}
return $key;
}