func pkcs5(data: NSData, blocksize: Int = 16) -> NSMutableData {
    var data = NSMutableData(data: data)
    let count = blocksize - data.length % blocksize

    for _ in 0...count {
        // somehow append the equivalent of chr(count) to data
    }

    return data
}

def pkcs5_pad(data, blocksize=16):
    pad_count = blocksize - len(data) % blocksize
    return data + (chr(pad_count) * pad_count).encode('utf-8')