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1import java.io.File;
2import java.io.FileInputStream;
3import java.io.FileOutputStream;
4import java.io.IOException;
5import java.nio.charset.Charset;
6import java.security.GeneralSecurityException;
7import java.security.NoSuchAlgorithmException;
8import java.security.SecureRandom;
9import java.util.Base64;
10
11import javax.crypto.Cipher;
12import javax.crypto.KeyGenerator;
13import javax.crypto.SecretKey;
14import javax.crypto.spec.GCMParameterSpec;
15import javax.crypto.spec.SecretKeySpec;
16
17public enum AES {
18
19    INSTANCE;
20
21    private static final String CIPHER_ALGORITHM = "AES";
22    private static final String ALGORITHM_MODE_PADDING = "AES/GCM/NoPadding";
23
24    private static final int IV_LENGTH_BYTES = 16;
25    private static final int AES_KEY_SIZE = 128;
26    private static final int GCM_TAG_LENGTH = 128;
27
28    public String encrypt(String plainText, String authenticationTag) throws GeneralSecurityException, IOException {
29        createKeyFile(authenticationTag);
30        Cipher cipher = Cipher.getInstance(ALGORITHM_MODE_PADDING);
31        final int blockSize = cipher.getBlockSize();
32        SecretKey secretKey = readKeyFile(authenticationTag);
33        byte[] plainTextByte = plainText.trim().getBytes(Charset.forName("UTF-8"));
34        byte[] ivBytes = generateIV();
35        cipher.init(Cipher.ENCRYPT_MODE, secretKey, new GCMParameterSpec(GCM_TAG_LENGTH, ivBytes));
36        cipher.updateAAD(authenticationTag.getBytes(Charset.forName("UTF-8")));
37        byte[] encryptedMessage = cipher.doFinal(plainTextByte);
38        byte iv_and_encryptedMessage[] = concatIvAndCipher(ivBytes, encryptedMessage, blockSize);
39        Base64.Encoder encoder = Base64.getEncoder().withoutPadding();
40        String iv_and_encryptedText = encoder.encodeToString(iv_and_encryptedMessage);
41        return iv_and_encryptedText;
42    }
43
44    public String decrypt(String iv_and_encryptedTextBase64, String authenticationTag)
45            throws GeneralSecurityException, IOException {
46        Cipher cipher = Cipher.getInstance(ALGORITHM_MODE_PADDING);
47        final int blockSize = cipher.getBlockSize();
48        Base64.Decoder decoder = Base64.getDecoder();
49        byte[] iv_and_encryptedMessage = decoder.decode(iv_and_encryptedTextBase64.trim());
50        byte[] ivBytes = extractIvFrom(iv_and_encryptedMessage, blockSize);
51        byte[] encryptedTextBytes = extractEncryptedMessageFrom(iv_and_encryptedMessage, blockSize);
52        SecretKey secretKey = readKeyFile(authenticationTag);
53        cipher.init(Cipher.DECRYPT_MODE, secretKey, new GCMParameterSpec(GCM_TAG_LENGTH, ivBytes));
54        cipher.updateAAD(authenticationTag.getBytes(Charset.forName("UTF-8")));
55        byte[] decryptedByte = cipher.doFinal(encryptedTextBytes);
56        String decryptedMessage = new String(decryptedByte, Charset.forName("UTF-8"));
57        return decryptedMessage;
58    }
59
60    private SecretKey readKeyFile(String tag) {
61
62    }
63
64    private void createKeyFile(String tag) {
65
66    }
67
68    public byte[] generateIV() throws NoSuchAlgorithmException {
69        SecureRandom random = new SecureRandom();
70        byte[] ivBytes = new byte[IV_LENGTH_BYTES];
71        random.nextBytes(ivBytes);
72        return ivBytes;
73    }
74
75    public byte[] concatIvAndCipher(byte[] iv, byte[] cipher, int blockSize) {
76        final byte[] ivAndEncryptedMessage = new byte[iv.length + cipher.length];
77        System.arraycopy(iv, 0, ivAndEncryptedMessage, 0, blockSize);
78        System.arraycopy(cipher, 0, ivAndEncryptedMessage, blockSize, cipher.length);
79        return ivAndEncryptedMessage;
80    }
81
82    public byte[] extractIvFrom(byte[] iv_and_encryptedMessage, int blockSize) {
83        byte[] ivBytes = new byte[blockSize];
84        System.arraycopy(iv_and_encryptedMessage, 0, ivBytes, 0, blockSize);
85        return ivBytes;
86    }
87
88    public byte[] extractEncryptedMessageFrom(byte[] iv_and_encryptedMessage, int blockSize) {
89        byte[] encryptedTextBytes = new byte[iv_and_encryptedMessage.length - blockSize];
90        System.arraycopy(iv_and_encryptedMessage, blockSize, encryptedTextBytes, 0, encryptedTextBytes.length);
91        return encryptedTextBytes;
92    }
93}