playfair.cpp

#include<iostream>
#include<string>
using namespace std;

class Playfair{
 
 public:
 	char keyMatrix[5][5];
 	string getKey(){
 		string k;
 		cout<<"Enter the key:\n";
 		cin>>k;
 		return k;
	
	 }
	string getMessage(){
		string m;
		cout<<"Enter the message:\n";
 		cin>>m;
 		return m;
	}
	//function for encryption 
 	void encrypt(string msg,string key){
 		makeKeyMatrix(key);
 		cout<<"----------Encryption Process------------"<<endl;
 		string bg = getBigrams(msg);
 		int n = bg.length();
 		char ct[n];//to store cipher text
 		int x=0;
 		while(x<n){
 		int a_row=0,a_col=0,b_row=0,b_col=0;
 		char ca=' ',cb=' ';
 	 	getPosition(bg[x],bg[x+1],a_row,a_col,b_row,b_col);
 	 	//cout<<a_row<<","<<a_col<<","<<b_row<<","<<b_col;
 	 	if(a_row==b_row){
 	 		ca= keyMatrix[a_row][mod((a_col+1),5)];
 	 		cb=	keyMatrix[b_row][mod((b_col+1),5)];
		  }
		else if(a_col==b_col){
			ca= keyMatrix[mod((a_row+1),5)][a_col];
			cb=	keyMatrix[mod((b_row+1),5)][b_col];
			
		}
		else{
			ca= keyMatrix[a_row][b_col];
			cb= keyMatrix[b_row][a_col];
			
		}
		
	cout<<bg[x]<<bg[x+1]<<"--->"<<ca<<cb<<endl;
	ct[x]=ca;
	ct[x+1]=cb;
	x+=2;
 	}
	cout<<"\n\n The cipher text is: \n" ;
 	for(int i=0;i<n;i++){
 		cout<<ct[i];
	 }
	}	
	
//function for decryption 
	void decrypt(string msg, string key){
			makeKeyMatrix(key);
 		cout<<"----------Decryption Process------------"<<endl;
 		//string bg = getBigrams(msg);
 		int n = msg.length();
 		char pt[n];//to store plain text
 		int x=0;
 		while(x<n){
 		int a_row=0,a_col=0,b_row=0,b_col=0;
 		char pa=' ',pb=' ';
 		char c1 = toupper(msg[x]);
 		char c2 = toupper(msg[x+1]);
 	 	getPosition(c1,c2,a_row,a_col,b_row,b_col);
 	 	//cout<<a_row<<","<<a_col<<","<<b_row<<","<<b_col;
 	 	if(a_row==b_row){
 	 		pa= keyMatrix[a_row][mod((a_col-1),5)];
 	 		pb=	keyMatrix[b_row][mod((b_col-1),5)];
		  }
		else if(a_col==b_col){
			pa= keyMatrix[mod((a_row-1),5)][a_col];
			pb=	keyMatrix[mod((b_row-1),5)][b_col];
			
		}
		else{
			pa= keyMatrix[a_row][b_col];
			pb= keyMatrix[b_row][a_col];
			
		}
		
	cout<<msg[x]<<msg[x+1]<<"--->"<<pa<<pb<<endl;
	pt[x]=pa;
	pt[x+1]=pb;
	x+=2;
 	}
	cout<<"\n\n The plain text is: \n" ;
 	for(int i=0;i<n;i++){
 		cout<<pt[i];
	 }
		
	}
 private:
	string getBigrams(string msg){
	int len = msg.length();
	char a[len]; //character array of given text 
	int n=0;
	char bigrams[len];
	for(int i =0;i<len;i++){
		if(msg[i]==' '){	//ignore space
			continue;
		}
		else if(msg[i]=='j'||msg[i]=='J'){
		a[n]= 'I'; //replace j or J  with I
		n++;	
		}else{
			a[n]= toupper(msg[i]); 
			n++;
		}
		
	}
	
	// to handle like balloon == ba lx lo on , and more
	int k=0;
	char filler='X';
	bool filled=false;
	for(int i=0;i<n;i+=2 ){
		bigrams[k]=a[i];
		k++;
		if(i+1!=n){
		 if(a[i]==a[i+1] && filled== false){
		 	bigrams[k]=filler;
		 	k++;
		 	bigrams[k]=a[i+1];
		 	k++;
		 	filled=true;
		 	continue;
		 }else{
		 	bigrams[k]=a[i+1];
		 	k++;
		 }
		 
		}
		
	}
	//cout<<k;
	 if(k%2!=0)	{
	 	bigrams[k]=filler;
	 	bigrams[k+1]='\0';
	 }else{
	 	bigrams[k]='\0';
	 }
	 return bigrams;
	}
	
	
	//function to generate key matrix
	void makeKeyMatrix(string text){
	int len = text.length();
	char ca[len]; //character array of given string excluding space
	int n=0;
	for(int i =0;i<len;i++){
		if(text[i]==' '){
			continue;
		}
		ca[n]= toupper(text[i]);
		n++;
	}
	
	//array of alphabets
	char alphabets[26];
	for(int i=0;i<26;i++){
		alphabets[i]=i+65;
	}
	
	char oneD[26];
	int p=0;
	oneD[0]=ca[0];
	for(int i=1; i<n;i++){
		bool duplicate=false;
		for(int j=0;j<i;j++){
			if(ca[i]==ca[j]){//avoid duplicates
			duplicate=true;
			break;	
			}	
		}
		if(duplicate==false){
			oneD[++p]=ca[i];
	}
	
	}
	if(p<26){
		for(int i = 0;i<26;i++){
			bool duplicate=false;
			for(int j=0;j<p;j++){
				if(alphabets[i]==oneD[j]){
					duplicate=true;
					break;
				}
			}
		if(duplicate==false){
		oneD[++p]=alphabets[i];
		}
	}
	//to store in keyMatrix
	p=0;
	for(int i= 0;i<5;i++){
		for(int j= 0;j<5;j++){
			if(oneD[p]=='J'){ //exclude J
				p++;
			}
			keyMatrix[i][j]=oneD[p];
			p++;
		}
	}
	cout<<"The key matrix for Playfair Cipher for given key is: \n";
	//to print keyMatrix
	
	for(int i= 0;i<5;i++){
		for(int j= 0;j<5;j++){
			
			cout<<keyMatrix[i][j]<<" ";
		}
		cout<<"\n";
	}

  }	
}

void getPosition(char a,char b,int &a_row,int &a_column,int &b_row, int &b_column) {
	bool match_a =false;
	bool match_b =false;
	for(int i=0;i<5;i++){
		for(int j =0;j<5;j++){
			if(keyMatrix[i][j]==a && match_a!=true){
					a_row= i;
					a_column=j;
					//cout<<keyMatrix[i][j];
					match_a = true;
			}
			if(keyMatrix[i][j]==b && match_b!=true){
					b_row= i;
					b_column=j;
					//cout<<keyMatrix[i][j];
					match_b = true;	
			}	
		}
		if(match_a && match_b){
		break;
		}
	}
}
int mod(int a, int b){ // to handle modulo operation 
	int c = a%b;
	if(c>=0)
		return c;
	else
		return b+c;
}
 	
};
int main(){
	cout<<"=======PALYFAIR CIPHER=========="<<endl<<endl;
	int choice;
	char more='y';
	Playfair p;
	string m,k;
	while(more=='y'){
		cout<<"Enter your choice as following :\n";
		cout<<"1. Press 1 for encryption "<<endl;
		cout<<"2. Press 2 for decryption "<<endl;
		cout<<"3. Press 3 for exit "<<endl;
		cin>>choice;
	switch(choice){
		case 1: 
			k= p.getKey();
			m= p.getMessage();
			p.encrypt(m,k);
			break;
		case 2: 
			k= p.getKey();
			m= p.getMessage();
			p.decrypt(m,k);
			break;
		case 3: 
			exit(1);
		default:
			cout<<"Invalid choice!!"<<endl;	
	}
	
	cout<<"\n\n Do you want to continue?(press y if you want)"<<endl;
	cin>>more;
 }
 }