A Java Program to perform encryption and decryption using Monoalphabetic Cipher

import java.util.*;

import java.net.*;

import java.io.*;

public class MonoAlphabeticSubstitutionCipher

{

 public char p[] = {'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'};

 public char ch[] = {'Q','W','E','R','T','Y','U','I','O','P','A','S','D','F','G','H','J','K','L','Z','X','C','V','B','N','M'};

 public String doEncryption(String s)

 {

                char c[]=new char[(s.length())];

                for(int i=0;i<s.length();i++)

                {

                                for(int j=0;j<26;j++)

                                {

                                                if(p[j]==s.charAt(i))  

                                                {

                                                                c[i]=ch[j];

                                                                break;   

                                                }

                                }

 }

 return(new String(c));

 }

 public String doDecryption(String s)

 {

                char p1[]=new char[(s.length())];

                 for(int i=0;i<s.length();i++)

                {

                for(int j=0;j<26;j++)

                {

                                if(ch[j]==s.charAt(i))  

                                {

                                                p1[i]=p[j];

                                                break;   

                                }

                }

  }

   return(new String(p1));

 }

                public static void main(String args[])

                {

                                String msg="helloworld";

                                String emsg,nmsg;

                                MonoAlphabeticSubstitutionCipher c1=new MonoAlphabeticSubstitutionCipher();

                                emsg= c1.doEncryption(msg);

                                System.out.println("\n\n Normal Text : " + msg);

                                System.out.println("\n\n Encrypted Text : " + emsg);

                                nmsg= c1.doDecryption(emsg);

                                System.out.println("\n\n main Decrypted Text : " + nmsg);

                }

}

/*End of the Program */

copy the above code in your desired editor , 

-> compile it with javac 

-> then run it with java

Below it the expected out put in a screen take.

Note: you will be prompted to enter your text, remember to use it your other applications before sending the information to the network for security preseasons.