PlayfairCipher.java

package src;

import java.util.Arrays;
import java.util.Scanner;

public class PlayfairCipher {
    static String removeDuplicate(String s) {
        int j, index = 0, len = s.length();
        char[] c = s.toCharArray();

        for (int i = 0; i < len; i++) {
            for (j = 0; j < i; j++) {
                if (c[i] == c[j]) break;
            }
            if (i == j) c[index++] = c[i];
        }
        s = new String((Arrays.copyOf(c, index)));
        return s;
    }

    static String removeWhiteSpace(char[] ch, String key) {

        char[] c = key.toCharArray();

        for (int i = 0; i < c.length; i++) {
            for (int j = 0; j < ch.length; j++) {
                if (c[i] == ch[j]) {
                    c[i] = ' ';
                    break;
                }
            }
        }

        key = new String(c);
        key = key.replaceAll(" ", "");
        return key;
    }

    static String makePair(String pt) {

        String s = "";

        for (int i = 0; i < pt.length(); i++) {
            if (pt.charAt(i) == ' ') continue;
            else {
                s += pt.charAt(i);
            }

            if (i < pt.length() - 1)
                if (pt.charAt(i) == pt.charAt(i + 1))
                    s += "x";
        }
        if (s.length() % 2 != 0)
            s += "x";
        System.out.println(s);

        return s;
    }

    static int[] findIJ(char a, char b, char[][] x) {

        int[] y = new int[4];
        if (a == 'j') a = 'i';
        else if (b == 'j') b = 'i';

        for (int i = 0; i < 5; i++) {
            for (int j = 0; j < 5; j++) {
                if (x[i][j] == a) {
                    y[0] = i;
                    y[1] = j;
                } else if (x[i][j] == b) {
                    y[2] = i;
                    y[3] = j;
                }
            }
        }

        if (y[0] == y[2]) {
            y[1] += 1;
            y[3] += 1;
        } else if (y[1] == y[3]) {
            y[0] += 1;
            y[2] += 1;
        }

        for (int i = 0; i < 4; i++) y[i] %= 5;
        return y;
    }

    static String encrypt(String pt, char[][] x) {

        char[] ch = pt.toCharArray();
        int[] a;

        for (int i = 0; i < pt.length(); i += 2) {
            if (i < pt.length() - 1) {
                a = findIJ(pt.charAt(i), pt.charAt(i + 1), x);

                if (a[0] == a[2]) {
                    ch[i] = x[a[0]][a[1]];
                    ch[i + 1] = x[a[0]][a[3]];
                } else if (a[1] == a[3]) {
                    ch[i] = x[a[0]][a[1]];
                    ch[i + 1] = x[a[2]][a[1]];
                } else {
                    ch[i] = x[a[0]][a[3]];
                    ch[i + 1] = x[a[2]][a[1]];
                }
            }
        }

        pt = new String(ch);
        return pt;
    }

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        System.out.print("Enter Plain text : ");
        String pt = sc.nextLine();

        System.out.print("Enter key : ");
        String key = sc.next();

        key = removeDuplicate(key);
        char[] ch = key.toCharArray();

        String st = "abcdefghiklmnopqrstuvwxyz";
        st = removeWhiteSpace(ch, st);
        char[] c = st.toCharArray();

        char[][] x = new char[5][5];
        int indexOfSt = 0, indexOfKey = 0;

        for (int i = 0; i < 5; i++) {
            for (int j = 0; j < 5; j++) {
                if (indexOfKey < key.length())
                    x[i][j] = ch[indexOfKey++];
                else
                    x[i][j] = c[indexOfSt++];
            }
        }

        for (int i = 0; i < 5; i++) {
            for (int j = 0; j < 5; j++)
                System.out.print(x[i][j] + " ");
            System.out.println();
        }

        pt = makePair(pt);
        pt = encrypt(pt, x);
        System.out.println(pt);
    }
}