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1Encryption in Java
2import java.security.*;
3import javax.crypto.*;
4import javax.crypto.spec.*;
5import java.io.*;
6
7/**
8 * This program generates a AES key, retrieves its raw bytes, and
9 * then reinstantiates a AES key from the key bytes.
10 * The reinstantiated key is used to initialize a AES cipher for
11 * encryption and decryption.
12 */
13public class AES
14{
15
16    /**
17     * Turns array of bytes into string
18     *
19     * @param buf   Array of bytes to convert to hex string
20     * @return  Generated hex string
21     */
22    public static String asHex(byte buf[])
23    {
24        StringBuilder strbuf = new StringBuilder(buf.length * 2);
25        int i;
26
27        for (i = 0; i &lt buf.length; i++)
28        {
29            if (((int) buf[i] & 0xff) &lt 0x10)
30            {
31                strbuf.append("0");
32            }
33
34            strbuf.append(Long.toString((int) buf[i] & 0xff, 16));
35        }
36
37        return strbuf.toString();
38    }
39
40    public static void main(String[] args) throws Exception
41    {
42
43        String message = "This is just an example";
44
45        // Get the KeyGenerator
46
47        KeyGenerator kgen = KeyGenerator.getInstance("AES");
48        kgen.init(128); // 192 and 256 bits may not be available
49
50
51        // Generate the secret key specs.
52        SecretKey skey = kgen.generateKey();
53        byte[] raw = skey.getEncoded();
54
55        SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
56
57
58        // Instantiate the cipher
59
60        Cipher cipher = Cipher.getInstance("AES");
61
62        cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
63
64        byte[] encrypted = cipher.doFinal(message.getBytes());
65        System.out.println("encrypted string: " + asHex(encrypted));
66
67        cipher.init(Cipher.DECRYPT_MODE, skeySpec);
68        byte[] original = cipher.doFinal(encrypted);
69        String originalString = new String(original);
70        System.out.println("Original string: " + originalString + " " + asHex(original));
71    }
72}