Question

The given plaintext is “Feistel cipher structure uses the same algorithm for both encryption and decryption”. Write Java or Python code to implement Shift cipher(Encryption and Decryption) and test your code on given plaintext. Your code must meet following conditions.

1. (5 points) User must enter the value of key from command prompt and print it at command prompt.
2. (2.5 points) Print the cipher text and the plaintext at the command prompt after encryption and decryption.
3. (2.5 points) Test your algorithm for 5 different key values and submit your screen shot of command prompt input and outputs.

Answer 1

Please let me know if anything is required. I am happy to help you.

Code in java :

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Scanner;

class Main
{
// Encrypts plain text using a shift cipher
public static StringBuffer encrypt(String text, int s)
{
StringBuffer result= new StringBuffer();
  
//loop to travel the string
for (int i=0; i<text.length(); i++)
{
if(text.charAt(i)!=' ') //condition to check the space in the string
{
  
if (Character.isUpperCase(text.charAt(i))) //condition to check the character is capital letter
{
//shifting the char using the given key
char ch = (char)(((int)text.charAt(i) +
s - 65) % 26 + 65);
result.append(ch); //after encryption adding the character in result string
}
else //condition to check the character is small letter
{
//shifting the char using the given key
char ch = (char)(((int)text.charAt(i) +
s - 97) % 26 + 97);
result.append(ch); //after encryption adding the character in result string
}
}
else
{
result.append(' '); //after encryption adding the space character in result string
}
}
return result; //returning the final result
}
  
// Decrypts cipher text using a shift cipher
public static StringBuffer decrypt(StringBuffer text, int s)
{
StringBuffer result= new StringBuffer();
  
//loop to travel the string
for (int i=0; i<text.length(); i++)
{
if(text.charAt(i)!=' ') //condition to check the space in the string
{
  
if (Character.isUpperCase(text.charAt(i))) //condition to check the character is capital letter
{
//shifting the char using the given key
char ch = (char)(((int)text.charAt(i) +
s - 65) % 26 + 65);
result.append(ch); //after decryption adding the character in result string
}
else //condition to check the character is small letter
{
//shifting the char using the given key
char ch = (char)(((int)text.charAt(i) +
s - 97) % 26 + 97);
result.append(ch); //after decryption adding the character in result string
}
}
else
{
result.append(' '); //after decryption adding the space character in result string
}
}
return result; //returning the final result
}
  
// Driver code
public static void main(String[] args) throws IOException
{
BufferedReader reader =
new BufferedReader(new InputStreamReader(System.in));

// Reading the plain_text
System.out.print("Enter plain text : ");
String plain_text = reader.readLine();
  
//reading the key
Scanner in = new Scanner(System.in);
System.out.print("Enter key : ");
int key = in.nextInt();

System.out.println("Key you entered is : " +key);
  
System.out.println("\n ***** After Encryption *****");
System.out.println("Plain Text is : " + plain_text);
  
//calling Encryption
StringBuffer cipher_text = encrypt(plain_text, key);
System.out.println("Cipher Text is : " + cipher_text);
  
System.out.println("\n ***** After Decryption *****");
System.out.println("Cipher Text is : " + cipher_text);
key = 26 - key;
  
//calling Decryption
System.out.println("Plain Text is : " + decrypt(cipher_text, key));
  
  
}
}

Test case 1 :

Test 2:

Test 3:

Test 4:

Test 5:

Test 6: