chqPMVmi

1import java.math.BigInteger;
2import java.nio.charset.StandardCharsets;
3
4import javax.crypto.Cipher;
5import javax.crypto.KeyGenerator;
6import javax.crypto.SecretKey;
7import javax.crypto.spec.GCMParameterSpec;
8
9public class Scribble {
10
11	public static void main(String[] args) throws Exception {
12
13		SecretKey secret = KeyGenerator.getInstance("AES").generateKey();
14		byte[] iv = new byte[16];
15		
16		Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
17		cipher.init(Cipher.ENCRYPT_MODE, secret, new GCMParameterSpec(128, iv));
18		
19		byte[] ctFromEmpty = cipher.doFinal(new byte[16]);
20		
21		cipher = Cipher.getInstance("AES/GCM/NoPadding");
22		cipher.init(Cipher.ENCRYPT_MODE, secret, new GCMParameterSpec(128, iv));
23		
24		byte[] plain = "--Hello World!--".getBytes(StandardCharsets.US_ASCII);
25		
26		byte[] ct = cipher.doFinal(plain);
27		
28		byte[] zeroCiphertext = new byte[16];
29		System.arraycopy(ctFromEmpty, 0, zeroCiphertext, 0, 16);
30		
31		byte[] targetCiphertext = new byte[16];
32		System.arraycopy(ct, 0, targetCiphertext, 0, 16);
33		
34		byte[] result = new BigInteger(1, zeroCiphertext).xor(new BigInteger(1,targetCiphertext)).toByteArray();
35		
36		System.out.println(new String(result, StandardCharsets.US_ASCII));
37	}
38}