playfair.cpp File Reference

#include <bits/stdc++.h>

Include dependency graph for playfair.cpp:

Macros
#define	ll   long long
#define	pb   push_back
#define	mp   make_pair

Functions
string	implmatrix (string s, char mat[][5])
int	main ()

Macro Definition Documentation

#define ll   long long

#define mp   make_pair

#define pb   push_back

Function Documentation

string implmatrix	(	string	s,
		char	mat[][5]
	)

The matrix obtained in the main function is now used here to generate the cipher text. According to playfair algorithm the conditions for swap vary according to the locations of the digrams in the supplied matrix.

< Iteration Variables for the matrix

First case handling

If the the digrams are not located in the same column and same row then we swap the take the digit in the same row but column number of the second member of the diagram and vice versa for the second element of the digram

Second case handling

If the the digrams are located in the same row and different column then we swap the take the digit in the same row but next column number in that row and same is done for the second element of the digram.

Third case handling

If the the digrams are located in the same colum and different row then we swap the take the digit in the same column but next row number in that row and same is done for the second element of the digram.

Parameters

s	String to be encrypted

                                             {
    pair<int,int> p[2];
    int i,j,k; 
    for(k=0;k<2;k++) {
        for(i=0;i<5;i++)
            for(j=0;j<5;j++)
                if(mat[i][j] == s[k]) {
                    p[k] = mp(i,j);
                }
    }
    /*Adhering the conditions for swapping values*/

    if(p[0].first != p[1].first && p[0].second != p[1].second) {
        s[0] = mat[p[0].first][p[1].second];
        s[1] = mat[p[1].first][p[0].second];
    }

    else if(p[0].first == p[1].first) {
        s[0] = mat[p[0].first][(p[0].second + 1) % 5];
        s[1] = mat[p[1].first][(p[1].second + 1) % 5];
    }

    else if(p[0].second == p[1].second) {
        s[0] = mat[(p[0].first + 1) % 5][p[0].second];
        s[1] = mat[(p[1].first + 1) % 5][p[1].second];
    }
    return s;
}

int main

(

)

           {
    string keyword = "PLAYFAIR";
    string message = "SECRETMESSAGEISECRET";
    char mat[5][5];
    int alpha[26] = {0};
    alpha[9] = 1;
    int keyw_len = keyword.size();
    int i, j, k, count = 0;
    for (i = 0; i < 5; i++) {
        for (j = 0; j < 5; j++) {
            if (count<keyw_len) {
                if(alpha[(int) (keyword[count] - 65)] == 0){mat[i][j] = (char) (keyword[count]);}
                else{j--;}
                alpha[(int) (keyword[count] - 65)] = 1;
                count++;
            } else {
                for (k = 0; k < 26; k++) {
                    if (alpha[k] == 0) {
                        mat[i][j] = (char) (65 + k);
                        alpha[k] = 1;
                        break;
                    }

                }
            }
        }
    }
    for(i = 0;i< 5;i++) {
        for (j = 0;j<5;j++) {
            cout << mat[i][j] <<" ";
        }
        cout << endl;
    }
    /*
     * Building the secret message for encryption
     *
     */
    int msg_len = message.size();
    vector<string> digrams;
    for (i = 0; i < msg_len; i++) {
        string ss;
        if (message[i] == message[i + 1]) {
            ss += message[i];
            ss += 'X';
        } else {
            ss += message[i];
            if (i + 1 < msg_len) { ss += message[i + 1]; }
            i++;
        }
        digrams.pb(ss);
        //cout << ss<<endl;
    }

    if (digrams[digrams.size() - 1].length() == 1) {
        digrams[digrams.size() - 1] += 'X';
    }
    int no_dig = digrams.size();
    string encrypted_string;
    for (i = 0; i < no_dig; i++) {
        digrams[i].c_str();
        string str = implmatrix(digrams[i], mat);
        encrypted_string+=str;
    }
    cout << "The original string is :" << message <<endl;
    cout << "The encrypted string is :" << encrypted_string << endl;
    return 0;
}

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