kVsT5sHc

1 
2import java.security.SecureRandom;
3import java.util.Scanner;
4import javax.crypto.Cipher;
5import javax.crypto.KeyGenerator;
6import javax.crypto.SecretKey;
7import javax.crypto.spec.SecretKeySpec;
8
9/*
10 * To change this license header, choose License Headers in Project Properties.
11 * To change this template file, choose Tools | Templates
12 * and open the template in the editor.
13 */
14/**
15 *
16 * @author xyz abc
17 */
18public class DiffieHellman {
19
20    /**
21     * @param args the command line arguments
22     */
23    public static void main(String[] args) throws Exception {
24        Scanner input = new Scanner(System.in);
25        System.out.print("Enter P value: ");
26        int p = input.nextInt();
27        System.out.print("Enter G value: ");
28        int g = input.nextInt();
29
30        int aRandom = 0;
31        int bRandom = 0;
32        int aPublicKey = 0;
33        int bPublicKey = 0;
34        int aSecret = 0;
35        int bSecret = 0;
36        int aSharedSecret = 0;
37        int bSharedSecret = 0;
38        for (aSecret = 1; aSecret < p; aSecret++) {
39            for (bSecret = 1; bSecret < p; bSecret++) {
40                aRandom = (int) (Math.pow(g, aSecret));
41                bRandom = (int) (Math.pow(g, bSecret));
42                aPublicKey = aRandom % p;
43                bPublicKey = bRandom % p;
44                aSharedSecret = (int) ((Math.pow(bPublicKey, aSecret)) % 13);
45                bSharedSecret = (int) ((Math.pow(aPublicKey, bSecret)) % 13);
46                if (aSharedSecret == bSharedSecret) {
47                    break;
48                }
49            }
50        }
51        System.out.println("aSecret key = " + aSecret + ", bSecret key=" + bSecret);
52        System.out.println("aRandom is " + aRandom + " and bRandom is " + bRandom);
53        System.out.println("The public key that should be sent from a to b is p= " + p + ", g= " + g + ", aPublicKey=" + aPublicKey);
54        System.out.println("The public key that should be sent from b to b is p= " + p + ", g= " + g + ", bPublicKey=" + bPublicKey);
55        System.out.println("The shared key that should be used in DES is: (" + aSharedSecret + ", " + bSharedSecret + ")");
56
57        System.out.print("Please enter a message to encrypt: ");
58        input = new Scanner(System.in);
59        String message = input.nextLine();
60        byte[] messageByte = message.getBytes();
61
62        //converting shared secret to string then bytes
63        byte[] skey = getRawKey((String.valueOf(aSharedSecret)).getBytes());
64        //encrypting
65        byte[] encryptedByte = encrypt(skey, messageByte);
66        String encryptedMessage = new String(encryptedByte);
67        System.out.println("The Cipher text is: " + encryptedMessage);
68
69        byte[] dbyte = decrypt(skey, encryptedByte);
70        String decryptedMessage = new String(dbyte);
71        System.out.println("Decrypted message " + decryptedMessage);
72
73    }
74
75    /**
76     * Method to generate encoded key using DES
77     *
78     * @param seed
79     * @return
80     * @throws Exception
81     */
82    private static byte[] getRawKey(byte[] seed) throws Exception {
83        KeyGenerator kgen = KeyGenerator.getInstance("DES");
84        SecureRandom sr = SecureRandom.getInstance("SHA1PRNG");
85        sr.setSeed(seed);
86        kgen.init(56, sr);
87        SecretKey skey = kgen.generateKey();
88        return skey.getEncoded();
89
90    }
91
92    /**
93     * Method to encrypt
94     *
95     * @param raw
96     * @param clear
97     * @return
98     * @throws Exception
99     */
100    private static byte[] encrypt(byte[] raw, byte[] clear) throws Exception {
101        SecretKeySpec skeySpec = new SecretKeySpec(raw, "DES");
102        Cipher cipher = Cipher.getInstance("DES");
103        cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
104        byte[] encrypted = cipher.doFinal(clear);
105        return encrypted;
106    }
107
108    /**
109     * Method to decrypt
110     *
111     * @param raw
112     * @param encrypted
113     * @return
114     * @throws Exception
115     */
116    private static byte[] decrypt(byte[] raw, byte[] encrypted) throws Exception {
117        SecretKeySpec skeySpec = new SecretKeySpec(raw, "DES");
118        Cipher cipher = Cipher.getInstance("DES");
119        cipher.init(Cipher.DECRYPT_MODE, skeySpec);
120        byte[] decrypted = cipher.doFinal(encrypted);
121        return decrypted;
122    }
123
124}