FourSquareCipher.java

import java.util.Scanner;

public class FourSquareCipher{
	
	//aggregate 2-D char array (10 X 10)
	static char[][] aggregate = new char[10][10];
	
	//TL,TR,BL,BR 2-D char array (each one 5 X 5)
	static char[][] TL=new char[5][5], TR=new char[5][5]; 
	static char[][] BL=new char[5][5], BR=new char[5][5];
	
	//encryption function
	static String encrypt(String pt, String key1, String key2) {
		String encpt = new String("");
				
		int n=-1;
		for(int i=0;i<key1.length();i++) {
			n+=1;
			n%=5;
			int m=(int)(i/5);
			TR[m][n]=key1.charAt(i);
		}
		n=-1;
		for(int i=0;i<key2.length();i++) {
			n+=1;
			n%=5;
			int m=(int)(i/5);
			BL[m][n]=key2.charAt(i);
		}
		int num = 64;
		for(int i=0;i<5;i++)
			for(int j=0;j<5;j++) {
				num++;
				if(num==74)
					num++;
				TL[i][j]=(char)num;
				BR[i][j]=(char)num;
			}
		String seq = new String("");
		for(int i=0;i<5;i++) {
			for(int j=0;j<10;j++) {
				if(j>4) {
					int k=j-5;
					seq=seq+TR[i][k];
				}
				else {
					seq=seq+TL[i][j];
				}
			}
		}
		for(int i=0;i<5;i++) {
			for(int j=0;j<10;j++) {
				if(j>4) {
					int k=j-5;
					seq=seq+BR[i][k];
				}
				else {
					seq=seq+BL[i][j];
				}
			}
		}
		int ctr=-1;
		for(int i=0;i<10;i++)
			for(int j=0;j<10;j++) {
				ctr++;
				aggregate[i][j]=seq.charAt(ctr);
			}
		
		for(int i=0;i<pt.length();i=i+2) {
			int row=0, col=0;
			for(int j=0;j<5;j++)
				for(int k=0;k<5;k++) {
					if(TL[j][k]==pt.charAt(i)) {
						row = j;
						break;
					}
					if(row!=0)
						break;
				}
			for(int j=0;j<5;j++)
				for(int k=0;k<5;k++) {
					if(BR[j][k]==pt.charAt(i+1)) {
						col = k+5;
						break;
					}
					if(col!=0)
						break;
				}
			encpt = encpt + Character.toString(aggregate[row][col]);
			row = 0; col = 0;
			for(int j=0;j<5;j++)
				for(int k=0;k<5;k++) {
					if(BR[j][k]==pt.charAt(i+1)) {
						row = j+5;
						break;
					}
					if(row!=0)
						break;
				}
			for(int j=0;j<5;j++)
				for(int k=0;k<5;k++) {
					if(TL[j][k]==pt.charAt(i)) {
						col = k;
						break;
					}
					if(col!=0)
						break;
				}
			encpt = encpt + Character.toString(aggregate[row][col]);
		}
		return encpt;
	}
	
	//decryption function
	static String decrypt(String encpt, String key1, String key2) {
		String decpt = new String("");
		for(int i=0; i<encpt.length(); i=i+2) {
			int row=0, col=0;
			for(int j=0;j<5;j++)
				for(int k=0;k<5;k++) {
					if(TR[j][k]==encpt.charAt(i)) {
						row = j;
						break;
					}
					if(row!=0)
						break;
				}
			for(int j=0;j<5;j++)
				for(int k=0;k<5;k++) {
					if(BL[j][k]==encpt.charAt(i+1)) {
						col = k;
						break;
					}
					if(col!=0)
						break;
				}
			decpt = decpt + Character.toString(aggregate[row][col]);
			row = 0; col = 0;
			for(int j=0;j<5;j++)
				for(int k=0;k<5;k++) {
					if(BL[j][k]==encpt.charAt(i+1)) {
						row = j+5;
						break;
					}
					if(row!=0)
						break;
				}
			for(int j=0;j<5;j++)
				for(int k=0;k<5;k++) {
					if(TR[j][k]==encpt.charAt(i)) {
						col = k+5;
						break;
					}
					if(col!=0)
						break;
				}
			decpt = decpt + Character.toString(aggregate[row][col]);
		}
		return decpt;
	}
	
	//main function
	public static void main(String[] args) {
		
		System.out.print("Enter plaintext: ");
		Scanner scan = new Scanner(System.in);
		String pt = scan.nextLine();
		System.out.print("Enter key 1: ");
		String key1 = scan.nextLine();
		System.out.print("Enter key 2: ");
		String key2 = scan.nextLine();
		String encpt = encrypt(pt,key1,key2);
		String decpt = decrypt(encpt,key1,key2);
		System.out.println("Encrypted text: "+encpt);
		System.out.println("Decrypted text: "+decpt);
		scan.close();
		
	}
	
}