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VigenèreCipher.cpp
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VigenèreCipher.cpp
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/*
👉 In cryptography, the Vigenère Cipher is a method of encrypting alphabetic text by using a series of interwoven Caesar Cipher.
Steps
=====
⇒ Convert all uppercase character into lowercase in the plain text.
⇒ Check if plain text has no intergral characters.
⇒ Input cipher key.
⇒ No. all characters from a - z as 0 - 25.
⇒ Find cipher text by : (characterNum + keyNum) mod 26.
, where characterNum and keyNum are the no.s associated with plain text and cipher key characters.
*/
// including header files
#include<iostream> // input-output statements
#include<map> // for alphabetic codes
#include<vector> // for vector
#include<algorithm> // for find() : find element in vector, transform() : to convert to lowercase
using namespace std;
// function for encryption
string encryptPlainText(string plainText, string key, map<char, int> map) {
vector<int> cipherCode; // for integer codes of cipher text
string cipherTxt = ""; // for cipher text
// convert into cipher code
for(int i = 0; i < plainText.length(); i++)
// cipher value = (plain + key) % 26
cipherCode.push_back((map[plainText[i]] + map[key[i]]) % 26);
// decode cipher value into cipher text
for(int i : cipherCode) {
// search cipher code in alphabetic code map
for(auto j : map) {
// get character associated with code
if(j.second == i) cipherTxt += j.first;
}
}
return cipherTxt; // return obtained cipher text
}
// main function
int main() {
string plainTxt, key; // for plain & cipher key
map<char, int> alphaCode; // for integer codes for alphabets
// alphabet codes
alphaCode['a'] = 0;
alphaCode['b'] = 1;
alphaCode['c'] = 2;
alphaCode['d'] = 3;
alphaCode['e'] = 4;
alphaCode['f'] = 5;
alphaCode['g'] = 6;
alphaCode['h'] = 7;
alphaCode['i'] = 8;
alphaCode['j'] = 9;
alphaCode['k'] = 10;
alphaCode['l'] = 11;
alphaCode['m'] = 12;
alphaCode['n'] = 13;
alphaCode['o'] = 14;
alphaCode['p'] = 15;
alphaCode['q'] = 16;
alphaCode['r'] = 17;
alphaCode['s'] = 18;
alphaCode['t'] = 19;
alphaCode['u'] = 20;
alphaCode['v'] = 21;
alphaCode['w'] = 22;
alphaCode['x'] = 23;
alphaCode['y'] = 24;
alphaCode['z'] = 25;
cout << "\t====== VIGENERE CIPHER =======" << endl;
// input plain text
cout << "\nEnter Plain Text : ";
getline(cin, plainTxt);
// input cipher key
cout << "\nEnter Cipher Key : ";
cin >> key;
// convert all characters in plain text to lowercase
transform(plainTxt.begin(), plainTxt.end(), plainTxt.begin(), ptr_fun<int, int>(tolower));
// if key & plain text not of equal length
if(key.length() < plainTxt.length()) {
// append
for(int i = 0; key.length() < plainTxt.length(); i++) key += key[i];
}
// display output
cout << "\nPLAIN TEXT : " << plainTxt << endl;
cout << "CIPHER TEXT (Encrypted Text) : " << encryptPlainText(plainTxt, key, alphaCode); // function call
return 0;
}