Cryptography : Playfair Cipher

Cryptography : Playfair Cipher

  1:03 PM    mayuravaani

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Playfair Cipher

Sample java code for Playfair Cipher

Encryption

//playfair encryption: i and j count as one letter

import java.util.*;

public class playfair_encry{

public static void main(String args[]){

Scanner myscanner=new Scanner(System.in);

System.out.println("Enter the keyword");

String key=myscanner.nextLine().toLowerCase().replace(" ","").replace("j","i");

String alpha="abcdefghiklmnopqrstuvwxyz";

char array[][];

array=new char[5][5];

char arraykey[];

arraykey=new char[key.length()];

arraykey[0]=key.charAt(0);

int m=1;

//inserting the keyword into arraykey without repeating letters

for(int i=1;i<key.length();i++){

char a=key.charAt(i);

boolean found=false;

for(int j=0;j<key.length();j++){

if(a==arraykey[j]){

found=true;

}

}

if(found==false){

arraykey[m]=a;

m++;

}

}

//inserting into the array from arraykey

int k=0;

for(int i=0;i<=4;i++){

for(int j=0;j<=4;j++){

if(k<key.length()){

if(arraykey[k]!='\u0000'){

array[i][j]=arraykey[k];

k++;

}

}

}

}

//inserting the alphabet letters-arraykey into the arraykey2

char arraykey2[];

arraykey2=new char[alpha.length()];

int p=0;

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

boolean found=false;

char a=alpha.charAt(i);

for(int j=0;j<arraykey.length;j++){

if(arraykey[j]==a){

found=true;

}

}

if(found==false){

arraykey2[p]=a;

p++;

}

}

//insert the elements from arraykey2 into array

int q=0;

for(int j=k%5;j<=4;j++){

if(q<arraykey2.length){

if(arraykey2[q]!='\u0000'){

array[k/5][j]=arraykey2[q];

q++;

}

}

}

for(int i=k/5+1;i<=4;i++){

for(int j=0;j<=4;j++){

if(q<arraykey2.length){

if(arraykey2[q]!='\u0000'){

array[i][j]=arraykey2[q];

q++;

}

}

}

}

System.out.println();

//print  the matrix

for(int i=0;i<=4;i++){

for(int j=0;j<=4;j++){

System.out.print(array[i][j]);

}

System.out.println();

}

System.out.println();

System.out.println("plain text");

String word=myscanner.nextLine().toLowerCase().replace(" ","").replace("j","i");

System.out.println();

System.out.println("cipher text (i & j count as one letter)");

//changing the plaintext to be pair

for(int i=0;i<word.length();i=i+2){

char a=word.charAt(i);

char b='\u0000';

if(i+1<word.length()){

b=word.charAt(i+1);

}

if(a==b){

word=word.substring(0,i+1).concat("x".concat(word.substring(i+1,word.length())));

}

}

if(word.length()%2==1){

word=word.concat("x");

}

//finding the array index and substituting the letters

int ai=0,aj=0,bi=0,bj=0;

for(int n=0;n<word.length();n=n+2){

char a=word.charAt(n);

char b=word.charAt(n+1);

for(int i=0;i<=4;i++){

for(int j=0;j<=4;j++){

if(a==array[i][j]){

ai=i;

aj=j;

}

if(b==array[i][j]){

bi=i;

bj=j;

}

}

}

if(bj==aj && ai!=4){

System.out.print(array[ai+1][bj]);

}

if(bj==aj && ai==4){

System.out.print(array[0][bj]);

}

if(bj==aj &&  bi!=4){

System.out.print(array[bi+1][aj]);

}

if(bj==aj && bi==4){

System.out.print(array[0][bj]);

}

if(bi==ai && aj!=4){

System.out.print(array[bi][aj+1]);

}

if(bi==ai && aj==4){

System.out.print(array[ai][0]);

}

if(bi==ai && bj!=4){

System.out.print(array[ai][bj+1]);

}

if(bi==ai &&  bj==4){

System.out.print(array[bi][0]);

}

if(ai!=bi && bj!=aj){

System.out.print(array[ai][bj]);

System.out.print(array[bi][aj]);

}

}

}

}

output of the above code

                                                                     Decryption

//playfair encryption: i and j count as one letter.no of letters in ciphertext be even no;
import java.util.*;
public class playfair_decry{
public static void main(String args[]){
Scanner myscanner=new Scanner(System.in);
System.out.println("Enter the keyword");
String key=myscanner.nextLine().toLowerCase().replace(" ","").replace("j","i");
String alpha="abcdefghiklmnopqrstuvwxyz";
char array[][];
array=new char[5][5];
char arraykey[];
arraykey=new char[key.length()];
arraykey[0]=key.charAt(0);
int m=1;
//inserting the keyword into arraykey without repeating letters
for(int i=1;i<key.length();i++){
char a=key.charAt(i);
boolean found=false;
for(int j=0;j<key.length();j++){
if(a==arraykey[j]){
found=true;
}
}
if(found==false){
arraykey[m]=a;
m++;
}
}
//inserting into the array from arraykey
int k=0;
for(int i=0;i<=4;i++){
for(int j=0;j<=4;j++){
if(k<key.length()){
if(arraykey[k]!='\u0000'){
array[i][j]=arraykey[k];
k++;
}
}
}
}
//inserting the alphabet letters-arraykey into the arraykey2
char arraykey2[];
arraykey2=new char[alpha.length()];
int p=0;
for(int i=0;i<alpha.length();i++){
boolean found=false;
char a=alpha.charAt(i);
for(int j=0;j<arraykey.length;j++){
if(arraykey[j]==a){
found=true;
}
}
if(found==false){
arraykey2[p]=a;
p++;
}
}
//insert the elements from arraykey2 into array
int q=0;
for(int j=k%5;j<=4;j++){
if(q<arraykey2.length){
if(arraykey2[q]!='\u0000'){
array[k/5][j]=arraykey2[q];
q++;
}
}
}

for(int i=k/5+1;i<=4;i++){
for(int j=0;j<=4;j++){
if(q<arraykey2.length){
if(arraykey2[q]!='\u0000'){
array[i][j]=arraykey2[q];
q++;
}
}
}
}
System.out.println();
//print  the matrix
for(int i=0;i<=4;i++){
for(int j=0;j<=4;j++){
System.out.print(array[i][j]);
}
System.out.println();
}

System.out.println();
System.out.println("cipher text");
String word=myscanner.nextLine().toLowerCase().replace(" ","").replace("j","i");
System.out.println();
System.out.println("original text (i & j count as one letter)");
//finding the array index and substituting the letters
int ai=0,aj=0,bi=0,bj=0;
for(int n=0;n<word.length();n=n+2){
char a=word.charAt(n);
char b=word.charAt(n+1);
for(int i=0;i<=4;i++){
for(int j=0;j<=4;j++){
if(a==array[i][j]){
ai=i;
aj=j;
}
if(b==array[i][j]){
bi=i;
bj=j;
}
}
}

if(bj==aj && ai!=0){
System.out.print(array[ai-1][bj]);
}
if(bj==aj && ai==0){
System.out.print(array[4][bj]);
}
if(bj==aj &&  bi!=0){
System.out.print(array[bi-1][aj]);
}
if(bj==aj && bi==0){
System.out.print(array[4][bj]);
}

if(bi==ai && aj!=0){
System.out.print(array[bi][aj-1]);
}
if(bi==ai && aj==0){
System.out.print(array[ai][4]);
}
if(bi==ai && bj!=0){
System.out.print(array[ai][bj-1]);
}
if(bi==ai &&  bj==0){
System.out.print(array[bi][4]);
}

if(ai!=bi && bj!=aj){
System.out.print(array[ai][bj]);
System.out.print(array[bi][aj]);
}
}
}
}

output of the above code