CNS Lab 4th day

substitution_cipher.md

Caesar Cipher

#include <bits/stdc++.h>
using namespace std;

#define SHIFT 3

int main(int argc, char * argv[]) {
    string str, crypt;
    cout << "Enter string: ";
    getline(cin, str);
    for (int i=0; i < str.length(); i++) {
        if (islower(str[i]))
            crypt.push_back((str[i]-'a'+SHIFT)%26+ (int)'A');
        else
            crypt.push_back(str[i]);
    }
    cout << crypt << endl;
    return 0;
}

Monoalphabatic Cipher

#include <bits/stdc++.h>
using namespace std;
int keys[26];
int main(int argc, char * argv[]) {
    srand(time(0));
    string str, crypt;
    for (int i=0; i<26; i++)
        keys[i] = i;
    random_shuffle(keys, keys+26);
    cout << "Enter string: ";
    getline(cin, str);
    for (int i=0; i < str.length(); i++) {
        if (islower(str[i]))
            crypt.push_back(keys[(int)str[i]-'a']+'A');
        else
            crypt.push_back(str[i]);
    }
    cout << crypt << endl;
    return 0;
}

Playfair Cipher

#include <bits/stdc++.h>
using namespace std;
const string key="monarchy";
char poly[5][5];
map<char, pair<int, int> > look;

void fill_poly() {
    int arr[26];
    for (int i=0; i<26; i++)
	arr[i]=0;
    int in = 0;
    for (int i=0; i<key.length(); i++) {
	if (arr[key[i]-'a'] == 0) {
	    if (key[i] == 'i' || key[i] == 'j') {
		poly[in/5][in%5] = key[i] == i ? key[i]+32 : key[i]+31;
		arr['i'-'a'] = arr['j'-'a'] = 1;
	    } else {
	        poly[in/5][in%5] = key[i]-32;
	        arr[key[i]-'a'] = 1;
	    }
	    in++;
	}
    }
    
    for (int i=0; i<26; i++) {
	if (arr[i] == 0) {
	    if (i==8){
	    	poly[in/5][in%5] = 'I';
		arr[i] = 0;
		arr[++i] = 1;
	    }
	    poly[in/5][in%5] = 'A'+i;
	    in++;
	} 
    }
    // creating map of char to co-ordinates
    for (int i=0; i<5; i++)
	for (int j=0; j<5; j++)
	    look.insert(make_pair(poly[i][j]+32, make_pair(i,j)));
}

string cipher(string s) {
   if (s[0] == 'i') s[0] = 'j';
   if (s[1] == 'i') s[1] = 'j';
   pair<int, int> p1 = look[s[0]];
   pair<int, int> p2 = look[s[1]];
   string c="00";
   if (p1.first == p2.first) { // same row
	c[0] = poly[p1.first][(p1.second+1)%5];
	c[1] = poly[p2.first][(p2.second+1)%5];
   } else if (p1.second == p2.second) { // same col
	c[0] = poly[(p1.first+1)%5][p1.second];
	c[1] = poly[(p2.first+1)%5][p2.second];
   } else { // else anywhere on board
	c[0] = poly[p1.first][p2.second];
	c[1] = poly[p2.first][p1.second];
   }
   return c;
}

int main(int argc, char * argv[]) {
    string str, crypt="";
    fill_poly();
    for (int i=0; i<5; i++) {
    	for (int j=0; j<5; j++) 
		cout << poly[i][j] << " ";
    	cout << "\n";
    }
    cout << "Enter string: ";
    getline(cin, str);
    for (int i=0; i<str.length()-1; i+=2) {
	if (str[i] == str[i+1]) {
	    string s;
	    s.push_back(str[i]);
	    s.push_back((str[i]+1)%97+'a');
	    crypt += cipher(s);
	    i--;
	} else {
	    string s;
	    s.push_back(str[i]);
	    s.push_back(str[i+1]);
	    crypt += cipher(s);
	}
    }
    cout << crypt << endl;
    return 0;
}

Hill Cipher

#include <bits/stdc++.h>
using namespace std;

#define SHIFT 3
const string key = "computing";

int look[SHIFT][SHIFT];

void make_look() {
	for (int i=0; i<key.length(); i++) {
		look[i/SHIFT][i%SHIFT] = key[i]-'a';
	}
}

string cipher(string x) {
    int arr[SHIFT][1] = {{x[0]-'a'}, {x[1]-'a'}, {x[2]-'a'}};
    //int res[SHIFT][1] = {{0},{0},{0}};
    string c="";
    int res;
    for (int i=0; i < SHIFT; i++) {
    	for (int j=0; j < 1; j++) {
    		res = 0;
    		for (int k=0; k<SHIFT; k++) {
    			res += look[i][k]*arr[k][j];
    		}
    		c.push_back('a'+res%26);
    	}
    }
    return c;
}

int main(int argc, char * argv[]) {
    string str, crypt="";
    make_look();
    for (int i=0; i<SHIFT; i++) {
    	for (int j=0; j<SHIFT; j++) {
    		cout << setw(4) << (int)look[i][j];
    	}
    	cout << endl;
    }
    cout << "Enter string: ";
    getline(cin, str);
    for (int i=0; i < str.length(); i+=SHIFT) {
    	string s = str.substr(i, SHIFT);
    	crypt += cipher(s);
    }
    cout << crypt << endl;
    return 0;
}

Polyalphabatic Cipher

#include <bits/stdc++.h>
using namespace std;
#define ALPHA 26

char lookup[ALPHA][ALPHA];

void init() {
	for (int i=0; i<ALPHA; ++i) {
		for (int j = 0; j < ALPHA; ++j) {
			lookup[i][j] = 'A'+ (i%ALPHA+j)%ALPHA;
		}
	}
}

int main() {
	init();
	string key, text, cipher="";
	cout << "Enter Text: "; getline(cin, text);
	cout << "Enter Key: "; getline(cin, key);
	for (int i = 0; i < text.length(); ++i) {
		if (islower(text[i])) {
			cipher += lookup[text[i]-'a'][key[i]-'a'];
		}
	}
	cout <<"Cipher : ";
	cout << cipher << "\n";
	return 0;
}

// Key: deceptivedeceptivedeceptive 
// Text: wearediscoveredsaveyourself 
// Cipher: ZICVTWQNGRZGVTWAVZHCQYGLMGJ 

One-Time Pad Cipher

#include <bits/stdc++.h>
using namespace std;
#define ALPHA 27

int main() {
	string key, text, cipher="";
	cout << "Enter Text: "; getline(cin, text);
	cout << "Enter Key: "; getline(cin, key);
	int len = min(text.length(), key.length());
	int textlen = text.length();
	int keylen = key.length();
	int i;
	for (i = 0; i < len; ++i) {
		if (islower(text[i]) && islower(key[i])) {
			cipher += (text[i]-'a'+key[i]-'a')%ALPHA+'A';
		} else if (text[i] == 32) {
			cipher += key[i] == 'a' ? 'Z' : key[i]-33; 
		} else if (key[i] == 32) {
			cipher += text[i] == 'a' ? 'Z' : text[i]-33;
		}
	}
	for (int j=i; j < keylen; ++j) {
		cipher += key[j] == 'a' ? 'Z' : key[j]-33; 
	}
	for (int j=i; i < textlen; ++j) {
		cipher += text[j] == 'a' ? 'Z' : text[j]-33; 
	}
	cout <<"Cipher : ";
	cout << cipher << "\n";
	return 0;
}

/*
ciphertext: ANKYODKYUREPFJBYOJDSPLREYIUNOFDOIUERFPLUYTS
key:        pxlmvmsydofuyrvzwc tnlebnecvgdupahfzzlmnyih
plaintext:  mr mustard with the candlestick in the hall
*/