NAS Codes

1)Demonstrate use of symmetric encryption and decryption algorithm.

//Transposition(one of Encryption Technique)==NAS Prac_No-1

class Test_Transposition {

public static void main(String[] args){

String PlainText = "Welcome To Network Administration and Security";

String rst = transposition_encrypt(PlainText, 8);

System.out.println("Original Message==\n"+PlainText);

System.out.println("After Transposition==\n"+rst);

public static String transposition_encrypt(String plain, int Key){

int col = 0;

int a = 0;

String result = "";

String row;

col = plain.length()/Key;

if( plain.length()%Key != 0 )

col += 1;

char[] Plain_Arr = plain.toCharArray();

char[][] Plain_Arr2 = new char[col][Key];

for(int i=0;i<col;i++){

for(int j=0;j<Key;j++){

if(a<plain.length()){
 Plain_Arr2[i][j]=Plain_Arr[a++];

}else break;

for(int i=0;i<Key;i++){

for(int j=0;j<col;j++){

if(Plain_Arr2[j][i]!=0)

result += Plain_Arr2[j][i];

return result;

OP==

2) To implement a single DES

//DES==NAS Prac_No-2
import java.util.*;

import javax.crypto.BadPaddingException;

import javax.crypto.Cipher;

import javax.crypto.IllegalBlockSizeException;

import javax.crypto.KeyGenerator;

import javax.crypto.NoSuchPaddingException;

import javax.crypto.SecretKey;

import javax.crypto.SecretKeyFactory;

import javax.crypto.spec.DESKeySpec;

import java.io.*;

import java.security.InvalidKeyException;

import java.security.NoSuchAlgorithmException;

import java.security.spec.InvalidKeySpecException;

class DES{

public static void main(String[] args) throws IOException, NoSuchAlgorithmException,

String message="This is a confidential message.";

byte[] myMessage =message.getBytes(); //string to byte array as DES works on bytes

KeyGenerator Mygenerator = KeyGenerator.getInstance("DES");

SecretKey myDesKey = Mygenerator.generateKey();

Cipher myCipher = Cipher.getInstance("DES");

myCipher.init(Cipher.ENCRYPT_MODE, myDesKey);

byte[] myEncryptedBytes=myCipher.doFinal(myMessage);
 myCipher.init(Cipher.DECRYPT_MODE, myDesKey);

byte[] myDecryptedBytes=myCipher.doFinal(myEncryptedBytes);

String encrypteddata=new String(myEncryptedBytes);

String decrypteddata=new String(myDecryptedBytes);

System.out.println("Message : "+ message);

System.out.println("Encrypted - "+ encrypteddata);

System.out.println("Decrypted Message - "+ decrypteddata);

OP==

3)To implement a single AES

//AES==NAS Prac_No-3

import java.nio.charset.StandardCharsets;

import java.security.spec.KeySpec;
import java.util.Base64;

import javax.crypto.Cipher;

import javax.crypto.SecretKey;

import javax.crypto.SecretKeyFactory;

import javax.crypto.spec.IvParameterSpec;

import javax.crypto.spec.PBEKeySpec;

import javax.crypto.spec.SecretKeySpec;

class AES {

private static final String SECRET_KEY

= "my_super_secret_key_ho_ho_ho";

private static final String SALT = "ssshhhhhhhhhhh!!!!";

public static String encrypt(String strToEncrypt)

try {

byte[] iv = { 0, 0, 0, 0, 0, 0, 0, 0,

0, 0, 0, 0, 0, 0, 0, 0 };

IvParameterSpec ivspec

= new IvParameterSpec(iv);

SecretKeyFactory factory

= SecretKeyFactory.getInstance(

"PBKDF2WithHmacSHA256");

KeySpec spec = new PBEKeySpec(

65536, 256);

SecretKey tmp = factory.generateSecret(spec);

SecretKeySpec secretKey = new SecretKeySpec(

tmp.getEncoded(), "AES");

Cipher cipher = Cipher.getInstance(

"AES/CBC/PKCS5Padding");

cipher.init(Cipher.ENCRYPT_MODE, secretKey,

ivspec);

return Base64.getEncoder().encodeToString(

cipher.doFinal(strToEncrypt.getBytes(

StandardCharsets.UTF_8)));

catch (Exception e) {

System.out.println("Error while encrypting: "

+ e.toString());

return null;

public static String decrypt(String strToDecrypt)

try {

byte[] iv = { 0, 0, 0, 0, 0, 0, 0, 0,

0, 0, 0, 0, 0, 0, 0, 0 };

IvParameterSpec ivspec
 = new IvParameterSpec(iv);

SecretKeyFactory factory

= SecretKeyFactory.getInstance(

"PBKDF2WithHmacSHA256");

KeySpec spec = new PBEKeySpec(

SECRET_KEY.toCharArray(), SALT.getBytes(),

65536, 256);

SecretKey tmp = factory.generateSecret(spec);

SecretKeySpec secretKey = new SecretKeySpec(

tmp.getEncoded(), "AES");

Cipher cipher = Cipher.getInstance(

"AES/CBC/PKCS5PADDING");

cipher.init(Cipher.DECRYPT_MODE, secretKey,

ivspec);

return new String(cipher.doFinal(

Base64.getDecoder().decode(strToDecrypt)));

catch (Exception e) {

System.out.println("Error while decrypting: "

+ e.toString());

return null;

class AES_Main {
 public static void main(String[] args)

String originalString = "HelloPRMITR";

String encryptedString

= AES.encrypt(originalString);

String decryptedString

= AES.decrypt(encryptedString);

System.out.println("Oginal String=="+originalString);

System.out.println("Encrypted String=="+encryptedString);

System.out.println("Decrypted String=="+decryptedString);

OP==

4) To implement RSA encryption /decryption algorithm.

//RSA==NAS Prac_No-4

import java.math.*;
import java.util.*;

class Test_RSA {

public static void main(String args[])

int p, q, n, z, d = 0, e, i;

int msg = 12;

double c;

BigInteger msgback;

p = 3;

q = 11;

n = p * q;

z = (p - 1) * (q - 1);

System.out.println("the value of z = " + z);

for (e = 2; e < z; e++) {

if (gcd(e, z) == 1) {

break;

System.out.println("the value of e = " + e);

for (i = 0; i <= 9; i++) {

int x = 1 + (i * z);
 if (x % e == 0) {

d = x / e;

break;

System.out.println("the value of d = " + d);

c = (Math.pow(msg, e)) % n;

System.out.println("Encrypted message is : " + c);

BigInteger N = BigInteger.valueOf(n);

BigInteger C = BigDecimal.valueOf(c).toBigInteger();

msgback = (C.pow(d)).mod(N);

System.out.println("Decrypted message is : "

+ msgback);

static int gcd(int e, int z)

if (e == 0)

return z;

else

return gcd(z % e, e);

OP==
5)Diffie-Hellman key exchange (exponential key exchange)

//Diffie-Hellman key exchange==NAS Prac_No-5

import java.util.*;

class Test_DHAlgEx {

public static void main(String[] args)

long P, G, x, a, y, b, ka, kb;

Scanner sc = new Scanner(System.in);

System.out.println("Both the users should be agreed upon the public keys G and P");

System.out.println("Enter value for public key G:");

G = sc.nextLong();

System.out.println("Enter value for public key P:");

P = sc.nextLong();

System.out.println("Enter value for private key a selected by user1:");

a = sc.nextLong();

System.out.println("Enter value for private key b selected by user2:");

b = sc.nextLong();

x = calculatePower(G, a, P);
 y = calculatePower(G, b, P);

ka = calculatePower(y, a, P);

kb = calculatePower(x, b, P);

System.out.println("Secret key for User1 is:" + ka);

System.out.println("Secret key for User2 is:" + kb);

private static long calculatePower(long x, long y, long P)

long result = 0;

if (y == 1){

return x;

else{

result = ((long)Math.pow(x, y)) % P;

return result;

OP==
6) To find MAC (Message Authentication Code) algorithm for cryptographic checksum.

//MAC==NAS Prac_No-6

import java.security.Key;

import java.security.SecureRandom;

import javax.crypto.KeyGenerator;

import javax.crypto.Mac;

class Test_MacSample {

public static void main(String args[]) throws Exception{

KeyGenerator keyGen = KeyGenerator.getInstance("DES");

SecureRandom secRandom = new SecureRandom();

keyGen.init(secRandom);
 Key key = keyGen.generateKey();

Mac mac = Mac.getInstance("HmacSHA256");

mac.init(key);

String msg = new String("HelloPrmitrStudents");

byte[] bytes = msg.getBytes();

byte[] macResult = mac.doFinal(bytes);

System.out.println("Mac result:");

System.out.println(new String(macResult));

OP==

7) //MD==NAS Prac_No-7

import java.math.BigInteger;

import java.security.MessageDigest;

import java.security.NoSuchAlgorithmException;

class Test_MD5 {
 public static String getMd5(String input)

try {

MessageDigest md = MessageDigest.getInstance("MD5");

byte[] messageDigest = md.digest(input.getBytes());

BigInteger no = new BigInteger(1, messageDigest);

String hashtext = no.toString(16);

while (hashtext.length() < 32) {

hashtext = "0" + hashtext;

return hashtext;

catch (NoSuchAlgorithmException e) {

throw new RuntimeException(e);

public static void main(String args[]) throws NoSuchAlgorithmException

String s = "GeeksForGeeks";

System.out.println("Your HashCode Generated by MD5 is: " + getMd5(s));

}
OP==