682yxL9s

1import java.security.SecureRandom;
2import java.util.Arrays;
3import javax.crypto.Cipher;
4import javax.crypto.SecretKey;
5import javax.crypto.spec.IvParameterSpec;
6
7
8    public static void main(String[] args) throws Exception {
9    //Generate a random AES Key
10    SecretKey key1 = generateAESKey();
11    byte[] plainText = "some plain text".getBytes();
12
13    //Gerate random IV
14    byte[] iv = new byte[16];
15    SecureRandom random = new SecureRandom();
16    random.nextBytes(iv);
17
18    //Encrypt plainText using the generated key1 using CTR
19    byte[] encryptedWithKey1 = encryptCTR(plainText, iv, key1);
20    //Now encrypt the IV using key1 with ECB
21    byte[] encryptedIvWithKey1 = encryptECB(iv, key1);
22
23    //Generate another key
24    SecretKey key2 = generateAESKey();
25    //First decrypt IV with wrong key, which resuts in wrong IV
26    byte[] decryptedIvWithKey2 = decryptECB(encryptedIvWithKey1, key2);
27    //Using this wrong IV decrypt encrypted payload with wrong key
28    byte[] decryptedWithKey2 = decryptCTR(encryptedWithKey1, decryptedIvWithKey2, key2);
29
30    //Expect plaintext and decrypted cipher using wrong key to NOT be equal
31    System.out.println("should print false: " + Arrays.equals(plainText, decryptedWithKey2));
32}
33
34    private static byte[] encryptCTR(byte[] plainText, byte[] iv, SecretKey key) throws Exception {
35    IvParameterSpec ivParameterSpec = new IvParameterSpec(iv);
36
37    Cipher cipher = Cipher.getInstance("AES/CTR/NoPadding");
38    cipher.init(Cipher.ENCRYPT_MODE, key, ivParameterSpec);
39
40    return cipher.doFinal(plainText);
41}
42
43private static byte[] decryptCTR(byte[] encrypted, byte[] iv, SecretKey key) throws Exception {
44    IvParameterSpec ivParameterSpec = new IvParameterSpec(iv);
45
46    Cipher cipherDecrypt = Cipher.getInstance("AES/CTR/NoPadding");
47    cipherDecrypt.init(Cipher.DECRYPT_MODE, key, ivParameterSpec);
48    return cipherDecrypt.doFinal(encrypted);
49}
50
51private static byte[] encryptECB(byte[] plainText, SecretKey key) throws Exception {
52    Cipher cipher = Cipher.getInstance("AES/ECB/NoPadding");
53    cipher.init(Cipher.ENCRYPT_MODE, key);
54
55    return cipher.doFinal(plainText);
56}
57
58private static byte[] decryptECB(byte[] encrypted, SecretKey key) throws Exception {
59    Cipher cipherDecrypt = Cipher.getInstance("AES/ECB/NoPadding");
60    cipherDecrypt.init(Cipher.DECRYPT_MODE, key);
61    return cipherDecrypt.doFinal(encrypted);
62}
63    public static SecretKey generateAESKey() {
64    SecureRandom random = new SecureRandom();
65    byte[] keyBytes = new byte[16];
66    random.nextBytes(keyBytes);
67    SecretKeySpec key = new SecretKeySpec(keyBytes, "AES");
68    return key;
69}