7rBrazV6

1package code;
2
3import java.nio.ByteBuffer;
4import java.security.InvalidAlgorithmParameterException;
5import java.security.InvalidKeyException;
6import java.security.NoSuchAlgorithmException;
7
8import javax.crypto.BadPaddingException;
9import javax.crypto.Cipher;
10import javax.crypto.IllegalBlockSizeException;
11import javax.crypto.NoSuchPaddingException;
12import javax.crypto.SecretKey;
13import javax.crypto.spec.GCMParameterSpec;
14import javax.crypto.spec.SecretKeySpec;
15
16public class GCM {
17
18	private static final int KEY_LENGTH_IN_BYTES = 16;
19
20	public static void main(String[] args) throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException,
21			InvalidAlgorithmParameterException, IllegalBlockSizeException, BadPaddingException {
22		ByteArrayGenerator generator = new ByteArrayGenerator();
23
24		byte[] key = generator.generateRandomByteArray(KEY_LENGTH_IN_BYTES);
25		SecretKey secretKey = new SecretKeySpec(key, "AES");
26
27		byte[] iv = generator.generateRandomByteArray(12);
28
29		final Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
30		GCMParameterSpec parameterSpec = new GCMParameterSpec(KEY_LENGTH_IN_BYTES * 8, iv);
31		cipher.init(Cipher.ENCRYPT_MODE, secretKey, parameterSpec);
32
33
34		byte[] associatedData = generator.generateRandomByteArray(50);
35		if (associatedData != null) {
36		    cipher.updateAAD(associatedData);
37		}
38		
39		byte[] cipherText = cipher.doFinal("Super woopy secret".getBytes());
40		
41		System.out.println(new String(cipherText));
42		// ENC finished
43		
44		
45		ByteBuffer byteBuffer = ByteBuffer.allocate(4 + iv.length + cipherText.length);
46		byteBuffer.putInt(iv.length);
47		byteBuffer.put(iv);
48		byteBuffer.put(cipherText);
49		
50		
51		
52		
53		
54		// Transmission start
55		byte[] cipherMessage = byteBuffer.array();
56		// Transmission completed
57		
58		
59		
60		ByteBuffer byteBuffer2 = ByteBuffer.wrap(cipherMessage);
61		int ivLength = byteBuffer2.getInt();
62		if(ivLength < 12 || ivLength >= 16) { // check input parameter
63		    throw new IllegalArgumentException("invalid iv length");
64		}
65		byte[] iv2 = new byte[ivLength];
66		byteBuffer2.get(iv2);
67		byte[] cipherText2 = new byte[byteBuffer2.remaining()];
68		byteBuffer2.get(cipherText2);// same as loop .get() -> und in byte array schreiben
69		
70		
71		
72		final Cipher cipher2 = Cipher.getInstance("AES/GCM/NoPadding");
73		GCMParameterSpec parameterSpec2 = new GCMParameterSpec(KEY_LENGTH_IN_BYTES * 8, iv2);
74		cipher2.init(Cipher.DECRYPT_MODE, new SecretKeySpec(key, "AES"), parameterSpec2);
75		
76		if (associatedData != null) {
77		    cipher2.updateAAD(associatedData);
78		}
79		
80		byte[] decryptedCipherText = cipher2.doFinal(cipherText2);
81		System.out.println(decryptedCipherText);
82		System.out.println(new String(decryptedCipherText));
83	}
84
85}