我无法解密发送消息AES

Question

I have problem with decrypting message from UDP receive.

My code:

byte[] receiveData= new byte[1024];

DatagramPacket pakiet = new DatagramPacket(receiveData, receiveData.length);
udp.receive(pakiet);

String wiadomosc = new String(pakiet.getData());
publishProgress(wiadomosc);
String szyfr = main.preferences.getString("SZYFR_TCP", "");
if(!szyfr.equals("1"))
{
    enc = new Encryptor(kluczByte, getCode());
    Log.e("myApp", "jestem 2");
    Log.e("message = ","" + wiadomosc);

    wiadomosc = enc.decrypt(wiadomosc);
    publishProgress(wiadomosc);
}

In the log I saw that variable wiadomosc has data and many bad characters like this:

The byte array reciveData has 1024 elements. I think that my receive message is shorter, so it have to add elements to 1024. How to remove these characters from the string? Because I can't decrypt this string because I get a "corrupted pad block" exception.

Answer 1

I think that you just get the buffer returned when you call pakiet.getData() . So you could just call pakiet.getLength() to get to the exact amount of data within the buffer. If you call the decrypt function with the correct offset and length you should have more success.

Answer 2

UDP header contains the length of the UDP data. So there must be some API in java to extract that length. The length is in bytes. So initialize you receivedData wih that length.