PlayfairCipherN.java

import java.util.Scanner;
public class Main {
public static void main(String[] args) {
    Scanner in=new Scanner(System.in);
    System.out.print("Enter keyword: ");
    String key=in.nextLine();
    System.out.print("Enter message to encrypt: ");
    String msg=in.nextLine();

    PFEncryption pfEncryption=new PFEncryption();
    pfEncryption.makeArray(key);
    msg=pfEncryption.manageMessage(msg);
    pfEncryption.doPlayFair(msg, "Encrypt");
    String en=pfEncryption.getEncrypted();
    System.out.println("encrypted text is: " + en);
    System.out.println();
    System.out.println();
    pfEncryption.doPlayFair(en, "Decrypt");
    System.out.print("decrypted text is: " + pfEncryption.getDecrypted());
  }
}

class PFEncryption{

private char [][] alphabets= new char[5][5];
private char[] uniqueChar= new char[26];
private String ch="ABCDEFGHIKLMNOPQRSTUVWXYZ";
private String encrypted="";
private String decrypted="";

void makeArray(String keyword){
    keyword=keyword.toUpperCase().replace("J","I");
    boolean present, terminate=false;
    int val=0;
    int uniqueLen;
    for (int i=0; i<keyword.length(); i++){
        present=false;
        uniqueLen=0;
        if (keyword.charAt(i)!= ' '){
            for (int k=0; k<uniqueChar.length; k++){
                if (Character.toString(uniqueChar[k])==null){
                    break;
                }
                uniqueLen++;
            }
            for (int j=0; j<uniqueChar.length; j++){
                if (keyword.charAt(i)==uniqueChar[j]){
                    present=true;
                }
            }
            if (!present){
                uniqueChar[val]=keyword.charAt(i);
                val = val+1;
            }
        }
        ch=ch.replaceAll(Character.toString(keyword.charAt(i)), "");
    }

        for (int i=0; i<ch.length(); i++){
            uniqueChar[val]=ch.charAt(i);
            val++;
        }
    
        val=0;

        for (int i=0; i<5; i++){
            for (int j=0; j<5; j++){
                alphabets[i][j]=uniqueChar[val];
                val++;
                System.out.print(alphabets[i][j] + "\t");
            }
            System.out.println();
        }
    }

    String manageMessage(String msg){
    int val=0;
    int len=msg.length()-2;
    String newTxt="";
    String intermediate="";
    while (len>=0){
        intermediate=msg.substring(val, val+2);
        if (intermediate.charAt(0)==intermediate.charAt(1)){
            newTxt=intermediate.charAt(0) + "x" + intermediate.charAt(1);
            msg=msg.replaceFirst(intermediate, newTxt);
            len++;
        }
        len-=2;
        val+=2;
    }

    if (msg.length()%2!=0){
        msg=msg+'x';
        }
        return msg.toUpperCase().replaceAll("J","I").replaceAll(" ","");
    }

void doPlayFair(String msg, String tag){
    int val=0;
    while (val<msg.length()){
        searchAndEncryptOrDecrypt(msg.substring(val, val + 2), tag);
        val+=2;
    }
}

void searchAndEncryptOrDecrypt(String doubblyCh, String tag){
    char ch1=doubblyCh.charAt(0);
    char ch2=doubblyCh.charAt(1);
    int row1=0, col1=0, row2=0, col2=0;
    for (int i=0; i<5; i++){
        for (int j=0; j<5; j++){
            if (alphabets[i][j]==ch1){
                row1=i;
                col1=j;
            }
            else if(alphabets[i][j]==ch2){
                row2=i;
                col2=j;
            }
        }
    }
    if (tag=="Encrypt")
        encrypt(row1, col1, row2, col2);
    else if(tag=="Decrypt")
        decrypt(row1, col1, row2, col2);
}

void encrypt(int row1, int col1, int row2, int col2){
    if (row1==row2){
        col1=col1+1;
        col2=col2+1;
        if (col1>4)
            col1=0;
        if (col2>4)
            col2=0;
        encrypted+=(Character.toString(alphabets[row1][col1])+Character.toString(alphabets[row1][col2]));
    }else if(col1==col2){
        row1=row1+1;
        row2=row2+1;
        if (row1>4)
            row1=0;
        if (row2>4)
            row2=0;
        encrypted+=(Character.toString(alphabets[row1][col1])+Character.toString(alphabets[row2][col1]));
    }else{
        encrypted+=(Character.toString(alphabets[row1][col2])+Character.toString(alphabets[row2][col1]));
    }
}

void decrypt(int row1, int col1, int row2, int col2){
    if (row1==row2){
        col1=col1-1;
        col2=col2-1;
        if (col1<0)
            col1=4;
        if (col2<0)
            col2=4;
        decrypted+=(Character.toString(alphabets[row1][col1])+Character.toString(alphabets[row1][col2]));
    }else if(col1==col2){
        row1=row1-1;
        row2=row2-1;
        if (row1<0)
            row1=4;
        if (row2<0)
            row2=4;
        decrypted+=(Character.toString(alphabets[row1][col1])+Character.toString(alphabets[row2][col1]));
    }else{
        decrypted+=(Character.toString(alphabets[row1][col2])+Character.toString(alphabets[row2][col1]));
    }
}

String getEncrypted(){
    return encrypted;
}
String getDecrypted(){
    return decrypted;
}
}