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1package com.voiprec.ui;
2
3import android.util.Base64;
4
5import java.util.Random;
6
7import javax.crypto.Cipher;
8import javax.crypto.spec.IvParameterSpec;
9import javax.crypto.spec.SecretKeySpec;
10
11public class AesCrypto {
12
13    private static String CIPHER_NAME = "AES/CBC/PKCS5PADDING";
14
15    private static int CIPHER_KEY_LEN = 16; //128 bits
16
17    /**
18     * Encrypt data using AES Cipher (CBC) with 128 bit key
19     *
20     * @param key  - key to use should be 16 bytes long (128 bits)
21     * @param iv   - initialization vector
22     * @param data - data to encrypt
23     * @return encryptedData data in base64 encoding with iv attached at end after a :
24     */
25    public static String encrypt(String key, String data) {
26
27        try {
28
29            String iv = getRandomHexString();
30
31            System.out.println("random iv: " + iv);
32
33            IvParameterSpec ivSpec = new IvParameterSpec(iv.getBytes("UTF-8"));
34            SecretKeySpec secretKey = new SecretKeySpec(fixKey(key).getBytes("UTF-8"), "AES");
35
36            Cipher cipher = Cipher.getInstance(AesCrypto.CIPHER_NAME);
37            cipher.init(Cipher.ENCRYPT_MODE, secretKey, ivSpec);
38
39            byte[] encryptedData = cipher.doFinal((data.getBytes()));
40
41
42            String encryptedDataInBase64 = Base64.encodeToString(encryptedData, Base64.NO_WRAP);
43            String ivInBase64 = Base64.encodeToString(iv.getBytes("UTF-8"), Base64.NO_WRAP);
44
45            return encryptedDataInBase64 + ":" + ivInBase64;
46
47        } catch (Exception ex) {
48            throw new RuntimeException(ex);
49        }
50    }
51
52    private static String getRandomHexString(){
53        Random r = new Random();
54        StringBuilder sb = new StringBuilder();
55        while(sb.length() < 16){
56            sb.append(Integer.toHexString(r.nextInt()));
57        }
58
59        return sb.toString().substring(0, 16);
60    }
61
62    private static String fixKey(String key) {
63
64        if (key.length() < AesCrypto.CIPHER_KEY_LEN) {
65            int numPad = AesCrypto.CIPHER_KEY_LEN - key.length();
66
67            for (int i = 0; i < numPad; i++) {
68                key += "0"; //0 pad to len 16 bytes
69            }
70
71            return key;
72        }
73
74        if (key.length() > AesCrypto.CIPHER_KEY_LEN) {
75            return key.substring(0, CIPHER_KEY_LEN); //truncate to 16 bytes
76        }
77
78        return key;
79    }
80
81    /**
82     * Decrypt data using AES Cipher (CBC) with 128 bit key
83     *
84     * @param key  - key to use should be 16 bytes long (128 bits)
85     * @param data - encrypted data with iv at the end separate by :
86     * @return decrypted data string
87     */
88
89    public static String decrypt(String key, String data) {
90
91        try {
92            String[] parts = data.split(":");
93
94            IvParameterSpec iv = new IvParameterSpec(Base64.decode(parts[1],Base64.NO_WRAP));
95            SecretKeySpec secretKey = new SecretKeySpec(fixKey(key).getBytes("UTF-8"), "AES");
96
97            Cipher cipher = Cipher.getInstance(AesCrypto.CIPHER_NAME);
98            cipher.init(Cipher.DECRYPT_MODE, secretKey, iv);
99
100            byte[] decodedEncryptedData = Base64.decode(parts[0],Base64.NO_WRAP);
101
102            byte[] original = cipher.doFinal(decodedEncryptedData);
103
104            return new String(original);
105        } catch (Exception ex) {
106            throw new RuntimeException(ex);
107        }
108    }
109
110    public static void test() {
111
112        String key = "martin";
113        String plain_text = "catalin";
114
115        System.out.println("key=" + key + " (padded to 16byte/128bits)" + ", data = " + plain_text);
116
117        String encrypted = encrypt(key, plain_text);
118        System.out.println("key:iv = " + encrypted);
119
120        String decrypt = decrypt(key, encrypted);
121        System.out.println("decrypted = " + decrypt);
122    }
123}