Question

Binary file IO

Suppose a file has been encrypted using the Caesar cipher as described above, and you know the secret key. Write a program to decrypt (or decode) the file. Your program will prompt the user to enter an input file name for the encrypted file, an output file name for the unencrypted version of the input file, and the secret key.

Create a DataInputStream for the input file and a DataOutputStreams for the output file. Next, read the input file (the encrypted file) one byte at a time (use the method readByte), decode that byte, and then write the decoded byte to the output file (use the method writeByte). Don’t forget to close the output file (or output stream) if you didn’t use try-with-resources, when you are done writing to the file. Otherwise, your output file might get corrupted

Enter an input (or encrypted) file name: lab6E.txt
Enter an output (or unencrypted) file name: lab6D.txt
Enter the encryption key: 5

File is decrypted successfully!

Encrypted file text:
N%|nqq%jshw~uy%ymnx%knqj%zxnsl%Hfjxfw%hnumjw Hfjxfw%hnumjw%nx%sf
rji%fkyjw%Ozqnzx%Hfjxfw1%|mt%zxji%ny%ns%mnx%uwn{fyj%htwwjxutsijs
hj  Ozqnzx%Hfjxfw%|fx%f%Wtrfs%ljsjwfq%|mt%uqf~ji%f%rfotw%wtqj%ns
%jxyfgqnxmnsl%ymj%Wtrfs%Jrunwj  Ymnx%nx%f%y~uj%tk%xzgxynyzynts%h

numjw Ns%xzgxynyzynts%hnumjw%f%hmfwfhyjw%kwtr%ymj%uqfnsyj}y%nx%w
juqfhji%|nym%fstymjw%hmfwfhyjw3

Decrypted file text:
I will encrypt this file using Caesar cipher
Caesar cipher is named after Julius Caesar, who used it in his
private correspondence

Julius Caesar was a Roman general who played a major role in
establishing the Roman Empire

This is a type of substitution cipher
In substitution cipher a character from the plaintext is
replaced with another character.

Answer 1

Screenshot

Program

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Scanner;

public class CaesarCypher {

   public static void main(String[] args) {
       //Scanner object
       Scanner sc=new Scanner(System.in);
       //Prompt for input file name
       System.out.print("Enter an input (or encrypted) file name: ");
       String inputFile=sc.nextLine();
       //Prompt for output file name
       System.out.print("Enter an output (or unencrypted) file name: ");
       String outFile=sc.nextLine();
       //Prompt for key
       System.out.print("Enter the encryption key: ");
       int key=sc.nextInt();
       //Read write
        try {
           //Input stream
           InputStream input = new FileInputStream(inputFile);
            DataInputStream inp = new DataInputStream(input);
            //Output stream
            OutputStream output= new FileOutputStream(outFile);
            DataOutputStream out = new DataOutputStream(output);
            //Read data as byte
            int count = input.available();
            byte[] ary = new byte[count];
           inp.read(ary);
           //Decrypt each data
           for (byte bt : ary) {
                  char k = decrypt((char) bt,key);
                  out.write((byte)k);
              }
           //Close files
           out.close();
           inp.close();
       } catch (IOException e) {
           // TODO Auto-generated catch block
           e.printStackTrace();
       }
        System.out.println("File is decrypted successfully!");
   }
   //Decrypting method
   public static char decrypt(char val,int key) {
       if(val!='\n') {
           return (char) (((int) val -key));
       }
       return val;
   }
}

Output

Enter an input (or encrypted) file name: lab6E.txt
Enter an output (or unencrypted) file name: lab6D.txt
Enter the encryption key: 5
File is decrypted successfully!