這次，使用java來模擬現實playfair密碼加密解密過程

import java.util.HashSet;
import java.util.Scanner;


public class Test1 {
    public static char a[][] = new char[5][5];
    public static String Encryptkey = "";
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner input = new
 
  Scanner(System.in);

        System.out.println("Please input the key");
        String key = input.nextLine();

        System.out.println("Please input the clear key");
        String clearkey = input.nextLine();

        System.out.println("Please input the signture key");
        String signture = input.nextLine();

        System.out
 
.println("Output the key matrix");
        Keymatrix(key);
        OutputMatrix();

        System.out.println("Encrypt");
        Encrypt(clearkey, signture.toUpperCase());

        Dncrypt(Encryptkey);

    }

    private static void Dncrypt(String encryptkey2) {
        // TODO Auto-generated method stub
 

        String Dncryptkey = "";
        int m=0, n=0, o=0, p=0;
        for(int i=0; i<encryptkey2.length(); i+=2) {
            for(int j=0; j<5; j++) {
                for(int k=0; k<5; k++) {
                    if(a[j][k] == encryptkey2.charAt(i)) {
                        m=j;
                        n=k;
                    }
                    if(a[j][k] == encryptkey2.charAt(i+1)) {
                        o=j;
                        p=k;
                    }
                }
            }
            if(m==o) {
                Dncryptkey =Dncryptkey + a[m][(n+4)%5] + a[o][(p+4)%5];
            }
            else if(n==p) {
                Dncryptkey =Dncryptkey + a[(m+4)%5][n] + a[(o+4)%5][p];
            }
            else {
                Dncryptkey =Dncryptkey + a[o][n] + a[m][p];
            }
        }
        System.out.println(Dncryptkey);
        System.out.println();
    }

    private static void Encrypt(String clearkey, String signture) {
        // TODO Auto-generated method stub
        String Upperclearkey = clearkey.toUpperCase();
        String formatkey = "";
        for(int i=0; i<Upperclearkey.length(); i++) {
            if(Upperclearkey.charAt(i)>='A' && Upperclearkey.charAt(i) <'Z') {
                formatkey+=Upperclearkey.charAt(i);
            }
        }
        while(isOverFlow(formatkey)) {
            formatkey = addSignture(formatkey, signture);
        }
        if(formatkey.length()%2 !=0) {
            formatkey += signture;
        }

        getEncrypt(formatkey);

    }

    private static void getEncrypt(String formatkey) {
        // TODO Auto-generated method stub
        int m=0, n=0, o=0, p=0;
        for(int i=0; i<formatkey.length(); i+=2) {
            for(int j=0; j<5; j++) {
                for(int k=0; k<5; k++) {
                    if(a[j][k] == formatkey.charAt(i)) {
                        m=j;
                        n=k;
                    }
                    if(a[j][k] == formatkey.charAt(i+1)) {
                        o=j;
                        p=k;
                    }
                }
            }
            if(m==o) {
                Encryptkey =Encryptkey + a[m][(n+1)%5] + a[o][(p+1)%5];
            }
            else if(n==p) {
                Encryptkey =Encryptkey + a[(m+1)%5][n] + a[(o+1)%5][p];
            }
            else {
                Encryptkey =Encryptkey + a[o][n] + a[m][p];
            }
        }
        System.out.println(Encryptkey);
        System.out.println();

    }

    private static boolean isOverFlow(String formatkey) {
        // TODO Auto-generated method stub
        for(int i=0; i<formatkey.length() - formatkey.length()%2; i+=2) {
            if(formatkey.charAt(i) == formatkey.charAt(i+1)) {
                return true;
            }
        }
        return false;
    }

    private static String addSignture(String formatkey, String signture) {
        // TODO Auto-generated method stub
        String temp = "";
        for(int i=0; i<formatkey.length() - formatkey.length()%2; i+=2) {
            if(formatkey.charAt(i) == formatkey.charAt(i+1)) {
                temp = temp + formatkey.charAt(i) + signture.charAt(0) + formatkey.charAt(i+1);
            }
            else {
                temp = temp + formatkey.charAt(i) + formatkey.charAt(i+1);
            }
        }
        return temp;
    }

    private static void OutputMatrix() {
        for(int i=0; i<5; i++) {
            for(int j=0; j<5; j++) {
                System.out.print(a[i][j]+"  ");
            }
            System.out.println();
        }
        System.out.println();
    }

    private static void Keymatrix(String key) {
        // TODO Auto-generated method stub
        HashSet<Character> hs = new HashSet<Character>();
        String formatkey ="";
        String Upperkey = key.toUpperCase();
        for(int i=0; i<Upperkey.length(); i++) {
            if(Upperkey.charAt(i) >='A' && Upperkey.charAt(i) <'Z') {
                if(!hs.contains(Upperkey.charAt(i))) {
                    hs.add(Upperkey.charAt(i));
                    formatkey+=Upperkey.charAt(i);
                }
            }
        }

        for(char i='A'; i<'Z'; i++) {
            if(!hs.contains(i)) {
                formatkey+=i;
            }
        }

        int m = 0;
        for(int i=0; i<5; i++)
            for(int j=0; j<5; j++) {
                a[i][j] = formatkey.charAt(m);
                m ++;
            }

    }


}