Task 1a
import java.util.*;
class T1{
public static void main(String args[]){
Scanner sc=new Scanner(System.in);
System.out.println("Enter Plain Text:");
String txt=sc.next();
System.out.println("Enter key:");
int key=sc.nextInt();
txt=encrypt(txt,key);
System.err.println("Encrypted Text: "+txt);
txt=decrypt(txt,key);
System.err.println("Decrypted Text: "+txt);
}
static String encrypt(String txt,int key){
String etxt="";
for(int i=0;i<txt.length();i++){
char j=txt.charAt(i);
if(Character.isUpperCase(j)){
etxt+=(char)(((j-'A')+key)%26 +'A');
}
else etxt+=(char)(((j-'a')+key)%26 +'a');
}
return etxt;
}
static String decrypt(String txt,int key){
String etxt="";
for(int i=0;i<txt.length();i++){
char j=txt.charAt(i);
if(Character.isUpperCase(j)){
etxt+=(char)(((j-'A')-key+26)%26 +'A');
}
else etxt+=(char)(((j-'a')-key+26)%26 +'a');
}
return etxt;
}
}
Task 1b
import java.util.*;
class T1b{
static String abc="abcdefghijklmnopqrstuvwxyz";
public static void main(String args[]){
Scanner sc=new Scanner(System.in);
System.out.println("Enter Plain Text:");
String txt=sc.next();
txt=encrypt(txt);
System.err.println("Encrypted Text: "+txt);
txt=decrypt(txt);
System.err.println("Decrypted Text: "+txt);
}
static String encrypt(String txt){
String etxt="";
for (int i=0;i<txt.length();i++){
int a=abc.indexOf(txt.charAt(i));
etxt+=abc.charAt(25-a);
}
return etxt;
}
static String decrypt(String txt){
String etxt="";
for (int i=0;i<txt.length();i++){
int a=abc.indexOf(txt.charAt(i));
etxt+=abc.charAt(25-a);
}
return etxt;
}
}
Task 2,3,4,5
import javax.crypto.*;
public class T2 {
private static Cipher encryptCipher;
private static Cipher decryptCipher;
public static void main(String[] args) throws Exception{
KeyGenerator keygenerator = KeyGenerator.getInstance("RC4");
SecretKey secretKey = keygenerator.generateKey();
encryptCipher = Cipher.getInstance("RC4");
encryptCipher.init(Cipher.ENCRYPT_MODE, secretKey);
byte[] encryptedData = encryptData("Classified Information!");
decryptCipher = Cipher.getInstance("RC4");
decryptCipher.init(Cipher.DECRYPT_MODE, secretKey);
decryptData(encryptedData);
}
private static byte[] encryptData(String data) throws Exception {
System.out.println("Data Before Encryption :" + data);
byte[] dataToEncrypt = data.getBytes();
byte[] encryptedData = encryptCipher.doFinal(dataToEncrypt);
System.out.println("Encryted Data: " + encryptedData);
return encryptedData;
}
private static void decryptData(byte[] data) throws Exception {
byte[] textDecrypted = decryptCipher.doFinal(data);
System.out.println("Decryted Data: " + new String(textDecrypted));
}
}
Task 7
import java.io.*;
import java.math.BigInteger;
import java.util.Random;
public class T7 {
private BigInteger p;
private BigInteger q;
private BigInteger N;
private BigInteger phi;
private BigInteger e;
private BigInteger d;
private int bitlength = 1024;
private Random r;
public T7() {
r = new Random();
p = BigInteger.probablePrime(bitlength, r);
q = BigInteger.probablePrime(bitlength, r);
N = p.multiply(q);
phi = p.subtract(BigInteger.ONE).multiply(q.subtract(BigInteger.ONE));
e = BigInteger.probablePrime(bitlength / 2, r);
while (phi.gcd(e).compareTo(BigInteger.ONE) > 0 && e.compareTo(phi) < 0) {
e = e.add(BigInteger.ONE);
}
d = e.modInverse(phi);
}
public static void main(String[] args) throws IOException {
T7 rsa = new T7();
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
String testString;
System.out.println("Enter the plain text:");
testString = in.readLine();
byte[] encrypted = rsa.encrypt(testString.getBytes());
System.out.println("Encrypted String in Bytes: " + encrypted);
byte[] decrypted = rsa.decrypt(encrypted);
System.out.println("Decrypted String: " + new String(decrypted));
}
public byte[] encrypt(byte[] message) {
return (new BigInteger(message)).modPow(e, N).toByteArray();
}
public byte[] decrypt(byte[] message) {
return (new BigInteger(message)).modPow(d, N).toByteArray();
}
Task 8
import java.io.*;
import java.math.BigInteger;
public class T8
{
public static void main(String[]args)throws IOException
{
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
System.out.println("Enter prime number:");
BigInteger p=new BigInteger(br.readLine());
System.out.print("Enter primitive root of "+p+":");
BigInteger g=new BigInteger(br.readLine());
System.out.println("Enter value for x less than " +p+":");
BigInteger x=new BigInteger(br.readLine());
BigInteger R1=g.modPow(x,p);
System.out.println("R1="+R1);
System.out.print("Enter value for y less than "+p+":");
BigInteger y=new BigInteger(br.readLine());
BigInteger R2=g.modPow(y,p);
System.out.println("R2="+R2);
BigInteger k1=R2.modPow(x,p);
System.out.println("Key1 calculated :"+k1);
BigInteger k2=R1.modPow(y,p);
System.out.println("Key2 calculated :"+k2);
System.out.println("deffie hellman secret key Encryption has Taken");
}
}
Task 9,10
import java.security.*;
public class T9 {
public static void main(String[] args) {
try {
MessageDigest md = MessageDigest.getInstance("SHA1");
System.out.println("Message digest object info:");
System.out.println("Algorithm = " + md.getAlgorithm());
System.out.println("ToString = " + md.toString());
String input;
input = "";
md.update(input.getBytes());
byte[] output = md.digest();
System.out.println("\nSHA1(\"" + input + "\") = " + bytesToHex(output));
input = "abc";
md.update(input.getBytes());
output = md.digest();
System.out.println("\nSHA1(\"" + input + "\") = " + bytesToHex(output));
input = "abcdefghijklmnopqrstuvwxyz";
md.update(input.getBytes());
output = md.digest();
System.out.println("\nSHA1(\"" + input + "\") = " + bytesToHex(output));
} catch (Exception e) {
System.out.println("Exception: " + e);
}
}
public static String bytesToHex(byte[] b) {
char hexDigit[] = {
'0', '1', '2', '3', '4', '5', '6', '7',
'8', '9', 'A', 'B', 'C', 'D', 'E', 'F'
};
StringBuffer buf = new StringBuffer();
for (int j = 0; j < b.length; j++) {
buf.append(hexDigit[(b[j] >> 4) & 0x0f]);
buf.append(hexDigit[b[j] & 0x0f]);
}
return buf.toString();
}
Task 12
import java.security.*;
import java.util.Base64;
public class T12 {
public static void main(String[] args) throws Exception {
KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
kpg.initialize(1024);
KeyPair keyPair = kpg.genKeyPair();
byte[] data = "Sample Text".getBytes();
Signature sig = Signature.getInstance("MD5WithRSA");
sig.initSign(keyPair.getPrivate());
sig.update(data);
byte[] signatureBytes = sig.sign();
System.out.println("Signature: \n" + Base64.getEncoder().encodeToString(signatureBytes));
sig.initVerify(keyPair.getPublic());
sig.update(data);
System.out.println("Signature verification result: " + sig.verify(signatureBytes));
}
}
