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1public final class AesEncoder implements Encoder {
2
3    private final Cipher cipher;
4    private final Mac mac;
5    private final byte[] salt;
6    private final byte[] derivedPasswordVerifier;
7
8    // AesStrength is an Enum with AES strength constants like salt or mac length
9    public static AesEncoder create(AesStrength strength, char[] password) throws Exception {
10        KeySpec spec = new PBEKeySpec(password, salt, 1000, strength.getSize());
11        SecretKey secretKey = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1").generateSecret(spec);
12        byte[] iv = { 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
13
14        Cipher cipher = Cipher.getInstance("AES/CTR/NoPadding");
15        cipher.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(secretKey.getEncoded(), "AES"), new IvParameterSpec(iv));
16
17        Mac mac = Mac.getInstance("HmacSHA1");
18        mac.init(new SecretKeySpec(macKey, "HmacSHA1"));
19        return new AesEncoder(cipher, mac, salt, derivedPasswordVerifier);
20    }
21
22    private static byte[] generateSalt(AesStrength strength) {
23        SecureRandom random = new SecureRandom();
24        byte[] buf = new byte[strength.getSaltLength()];
25        random.nextBytes(buf);
26        return buf;
27    }
28
29    @Override
30    public void encrypt(byte[] buf, int offs, int len) {
31        try {
32            // buf is INPUT DATA WITH LENGTH 16 bytes (alwasy, because AES requires it)
33            cipher.update(buf, offs, len, buf);
34            mac.update(buf, offs, len);
35        } catch(Exception e) {
36            throw new Zip4jException(e);
37        }
38    }
39
40    // ...
41
42} 
43     
44private static void increment(byte[] b) {
45    int n = b.length - 1;
46    while ((n >= 0) && (++b[n] == 0)) {
47        n--;
48    }
49}