vigenere_homework

/*
  Program for Encryption/Decryption/Cracking Vigenere Cipher
  © Copyright 2020 Iwo Strzeboński
  Published under WTFPLv2
  Language: C++
 */

#include <iostream>
#include <fstream>
#include <string>
#include <algorithm>

using namespace std;

string * generate_tabula_recta(string alph) {
    int n = alph.length();
    string * arr = new string[n];

    for (int i = 0; i < n; i++) {
        arr[i] = alph.substr(i, n) + alph.substr(0, i);
    }

    return arr;
}

string encode_vigenere(string mess, string alph, string arr[], string key) {
    string crypt = "";
    int count = 0, i = 0, n = 0;

    for (int a = 0; a < mess.length(); a++) {
        if (n > key.length() - 1) {
            n = 0;
            count++;
        }
        i = alph.find(key[n]);

        bool boolean = false;

        for (int b = 0; b < alph.length(); b++) {
            if (arr[b][0] == mess[a]) {
                crypt += arr[b][i];
                boolean = true;
                break;
            }
        }

        if (boolean) n++; else crypt += mess[a];
    }

    return crypt + "\nkey repetitions: " + to_string(count);
}

string decode_vigenere(string crypt, string alph, string arr[], string key) {
    string mess = "";
    int i = 0, n = 0;

    for (int a = 0; a < crypt.length(); a++) {
        n = n > key.length() - 1 ? 0 : n;
        i = alph.find(key[n]);

        bool boolean = false;

        for (int b = 0; b < alph.length(); b++) {
            if (arr[b][i] == crypt[a]) {
                mess += arr[b][0];
                boolean = true;
                break;
            }
        }

        if (boolean) n++; else mess += crypt[a];
    }

    return mess;
}

string count_letters(string alph, string crypt) {
    string out = "";

    for (int i = 0; i < alph.length(); i++) {
        out += string(1, alph[i]) + ": " + to_string(count(crypt.begin(), crypt.end(), alph[i])) + "\n";
    }

    return out;
}

float crack_vigenere(string alph, string crypt) {
    int n = alph.length();
    int arr[n];

    int coincidence_index = 0, all_letters = 0;
    float out = 0;

    for (int i = 0; i < n; i++) {
        arr[i] = int(count(crypt.begin(), crypt.end(), alph[i]));
        all_letters += arr[i];
        coincidence_index += arr[i] * (arr[i] - 1);
    }

    out = all_letters - 1;
    out *= all_letters;
    out = coincidence_index / out;
    out -= 0.0385;
    out =  0.0285 / out;

    out = (int)(out * 100 + 0.5);
    return (float)out / 100;
}

int main() {
    string alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

    string * arr;
    string array[alphabet.length()];
    arr = generate_tabula_recta(alphabet);

    for (int i = 0; i < alphabet.length(); i++) {
        array[i] = * (arr + i);
    }

    delete[] arr;

    string mode = "", key = "", message = "", answer = "";

    ofstream output_file ("Vigenere_wyniki.txt", ofstream::out | ofstream::trunc);

    answer = "================|| Zadanie 77.1 ||================\n";
    key = "LUBIMYCZYTAC";
    ifstream file1 ("dokad.txt");
    getline(file1, message);
    file1.close();
    answer += encode_vigenere(message, alphabet, array, key);
    output_file << answer << '\n';

    answer = "================|| Zadanie 77.2 ||================\n";
    ifstream file2 ("szyfr.txt");
    getline(file2, message);
    getline(file2, key);
    file2.close();
    answer += decode_vigenere(message, alphabet, array, key);
    output_file << answer << '\n';

    answer = "================|| Zadanie 77.3 ||================\n";
    answer += string(count_letters(alphabet, message));
    answer += "key lenght: " + to_string(key.length()) + "\ncalculated key length: " + to_string(crack_vigenere(alphabet, message));
    output_file << answer;

    output_file.close();
    return 0;
}