Question

Problem

1. Write two computer programs to simulate a Unicode stream cipher that consists of both
encryption and decryption algorithms. The encryption program accepts inputs from an
existing text file, called “letter.txt.” The encryption program produces an output ciphertext
file, called “secret” The decryption program takes “secret” as input and decrypts it into a
plaintext, called “message.txt.”

- The random “seed” must be known, but be kept secure, by the pseudorandom number
generators in both encryption and decryption programs.

Note from me: Use Java.

Answer 1

PROGRAM :

//EncryptDecrypt.java

import javax.crypto.Cipher;

import javax.crypto.SecretKey;

import javax.crypto.KeyGenerator;

import java.io.File;

import java.io.FileNotFoundException;

import java.util.Scanner;

import java.io.FileWriter;

import java.io.IOException;

public class EncryptDecrypt{

public static void main(String[] args) {

try{

//Generate private key............

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

SecretKey myPrivateKey = key_generator.generateKey();

Cipher cipher;

cipher = Cipher.getInstance("DES");

//Read text from a file named letter.txt

String data = "";

try {

File readFile = new File("/Users/hari-mohan/Desktop/files/letter.txt");

Scanner sc = new Scanner(readFile);

while (sc.hasNextLine()) {

data = sc.nextLine();

}

System.out.println("Read data successfully.");

sc.close();

}

catch (FileNotFoundException e) {

System.out.println("File not found.");

}

//Encrypt the data................

byte[] byteData = data.getBytes("UTF8");

cipher.init(Cipher.ENCRYPT_MODE, myPrivateKey);

byte[] dataEncrypted = cipher.doFinal(byteData);

String s = new String(dataEncrypted);

System.out.println(s);

//Write the encrypted data into the file named secret.txt

try {

FileWriter fileWriter = new FileWriter("/Users/hari-mohan/Desktop/files/secret.txt");

fileWriter.write(s+"");

System.out.println("Write encrypted data successfully.");

fileWriter.close();

} catch (IOException e) {

System.out.println("An error occurred.");

}

//Decrypt the data................

cipher.init(Cipher.DECRYPT_MODE, myPrivateKey);

byte[] textDecrypted = cipher.doFinal(dataEncrypted);

s = new String(textDecrypted);

System.out.println(s);

//Write decrypted data into the file named message.txt

try {

FileWriter fileWriter = new FileWriter("/Users/hari-mohan/Desktop/files/message.txt");

fileWriter.write(s+"");

System.out.println("Write original data successfully.");

fileWriter.close();

} catch (IOException e) {

System.out.println("An error occurred.");

}

}catch(Exception e)

{

System.out.println("Exception"+e.getMessage());

}

}

}