Question

C. Design a RandomCipher class as a subclass of the substitutionCipher from exercise P-3.40, so that each instance of the class relies on a random permutation of letters for its mapping.

Answer 1

#include <iostream>

#include <string>

#include <ctime>

#include <stdlib.h>

#include <vector>

using namespace std;

class SubstitutionCipher

{

public:

    //Define your key which is a permutation of 26 alphabets

    string key;

    SubstitutionCipher()

    {

    }

    //Constructor to create an instance which initializes the key with the given permutation

    SubstitutionCipher(string k)

    {

        key = k;

    }

    //function to encode a string

    string encode(string data)

    {

        //initialize encoded data

        string encodedData = data;

        //replace each character in encodedData with the corresponding mapped data in key. We subtract a char with 'A' to get its position

        for (int i = 0; i < data.length(); i++)

            encodedData[i] = key.at(data.at(i) - 'A');

        //return the encoded data

        return encodedData;

    }

    //function to decode a string

    string decode(string data)

    {

        //initialize decoded data

        string decodedData = data;

        //replace each character in decodedData with the corresponding reverse mapped data in key. We add the position with 'A' to get the corresponding char

        for (int i = 0; i < data.length(); i++)

            decodedData[i] = key.find(data.at(i)) + 'A';

        //return the decoded data

        return decodedData;

    }

};

//RandomCipher is a subclass of SubstitutionCipher which initializes the key with random permutation

class RandomCipher : public SubstitutionCipher

{

public:

    RandomCipher()

    {

        key = getRandomKey();

    }

    string getRandomKey()

    {

        int m = 26;

        srand(time(NULL));

        bool repeat = false;

        string key = "abcdefghijklmnopqrstuvwxyz";

        char letter;

        for (int i = 0; i < m; i++)

        {

            do

            {

                repeat = false;

                letter = rand() % 26 + 65;   // generate new random number

                for (int j = 0; j <= i; j++) // iterate through the already generated numbers

                {

                    if (letter == key[j])

                    { // if the generated number already exists, do the while again

                        repeat = true;

                        break;

                    }

                }

            } while (repeat);

            key[i] = letter; // assign the unique number

            repeat = false;

        }

        return key;

    }

};

int main()

{

    RandomCipher cipher;

    string data = "DEBAJYOTI";

    string encodedData = cipher.encode(data);

    cout << data << " encoded as " << encodedData << endl;

    string decodedData = cipher.decode(encodedData);

    cout << encodedData << " decoded as " << decodedData;

}

//SAMPLE OUTPUT:

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