Playfair 密碼加密以及加密和解密規則的示例
關鍵字是 MONARCHY
,然後矩陣看起來像
通過從左到右和從上到下填充關鍵字的字母(減去重複)來構造矩陣,然後用字母順序填充剩餘的字母和剩餘的字母。根據以下規則,明文一次加密兩個字母:
-
獲取文字中的字元(plain / cipher)並建立一組兩個字元。如果文字中的字元數是奇數,則新增填充字母(通常我們使用’x’)。
Text =HELLO
然後它將成為
HE | 組 LL | 牛 -
落在矩陣的同一行中的兩個明文字母每個都被右邊的字母替換,該行的第一個元素迴圈跟隨最後一個。例如,ar 被加密為 RM。
-
落在同一列中的兩個明文字母每個都被下面的字母替換,列的頂部元素迴圈跟在最後一個字母之後。例如,mu 被加密為 CM。
-
否則,一對中的每個明文字母將由位於其自己行中的字母替換,而該列由另一個明文字母佔據。因此,hs 變為 BP 並且 ea 變為 IM(或 JM,如編碼器所希望的那樣)。
實現 Playfair 密碼的簡單 Java 程式如下:
import java.util.Scanner;
public class Playfair {
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("Encrypting....\n\nThe encrypted text is: " + en);
System.out.println("=======================================");
pfEncryption.doPlayFair(en, "Decrypt");
System.out.print("\nDecrypting....\n\nThe encrypted 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++;
}
}
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;
}
}