Hill Cipher In C#

Nilesh Jadav

3y51.8k8100Article

C#Encryption DecryptionMatrix OperationsSubstitution CipherHill CipherPolygraphic

8 Comments

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Manav Pandya10y ago
See Nilesh Jadav : http://nileshjadav.blogspot.in/2016/08/get-data-from-database-using-selected.html
Manav Pandya10y ago
Hi Nilesh Jadav i have commented one of your blog's post so check it out and reply me personally
- Nilesh Jadav10y ago
  I can't check that Manav, you have to give me the link where you commented! SOrry for the inconvenience.
Tomi Csete10y ago
Great effort :) :)
Manav Pandya10y ago
Impressive and clean easy explaination sir
- Nilesh Jadav10y ago
  Thank you manav ! Glad to hear that
Amatya Agyey10y ago
Great effort.. Keep it up bhai
- Nilesh Jadav10y ago
  Thank you amatys Gupta , hope it helps

Introduction

In my previous article, we saw about monoalphabetic cipher. Today, we will discuss yet another substitution technique – Hill Cipher, which is far better than monoalphabetic cipher.

Hill cipher works on a mathematical concept of a matrix. So, before going further, we should throw some light on the matrix.

According to Wikipedia, A matrix is a rectangular array of number, symbols, or expressions arranged in rows and columns.

m by n matrix

For example, a 2X2 matrix is comprised of two rows and two columns.

2by2 matrix

For example, a 2x3 matrix is comprised of two rows and three columns.

2by 3 matrix

We will skip other things, like how the actual matrix works. It is very simple, and if someone has a doubt about matrix operations, comment in the comment box. I’ll arrange an article on Matrix operations.

How does the Hill cipher work?

Suppose you want to encrypt the message – “Dr. Greer Rocks“. See the steps mentioned below to work on the encryption part of your plaintext.

Plaintext = = > Dr Greer Rocks

Step 1. From the Square matrix of 2X2 with a non-negative integer, where each element is less than 26, the matrix actually is given in the analysis part. Right now, we assume that we have the encryption matrix, as shown below.

encryption matrix

Step 2. Check that its determinant does not factor by 2 or 3, and if it exists, return to the step mentioned above, to change the Encryption matrix.

Determinant of m

The determinant of Matrix M is = -5, which is not actually the factor of 2 or 13, so we move on to the next step.

Step 3. Make a pair of your plaintext. If you have an odd number of letters, then repeat the last letter or just embed “X” into the plaintext. (You can add any other letter too.)

Pair the letters and declare their identity alphabetically, where A=1, B=2, C=3, and so on.

DR GREER ROCKS => [DR], [GR], [EE], [RR], [OC], [KS]

matrix

Step 4. Convert each pair into a plaintext vector and multiply with the encrypted matrix (M).

encrypted matrix

Step 5. Replace each new vector with residue module 26.

residue module

Step 6. Convert each Ciphertext vector into its corresponding position in the alphabet.

corresponding position

Step 7. Align the letter in a single line, and you will get your Ciphertext.

ciphertext

Implementation of Encryption of Hill Cipher in C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace Hill_Cipher
{
    class Program
    {
        static void Main(string[] args)
        {
            int i, j, sum = 0, end = 0;
            int[,] mtrx = new int[25, 25];
            int[,] ans = new int[25, 1];
            string text = "";
            Console.WriteLine("Enter your Plaintext");
            Console.Write("\n");
            text = Console.ReadLine();
            Console.Write("\n");
            char[] txt = text.ToCharArray();
            end = txt.Length;
            for (i = 0; i < end; i++)
            {
                txt[i] = Convert.ToChar(txt[i] - 'a');
            }
            Random rnd = new Random();
            for (i = 0; i < end; i++)
            {
                for (j = 0; j < end; j++)
                {
                    mtrx[i, j] = rnd.Next();
                }
            }
            for (i = 0; i < end; i++)
            {
                sum = 0;
                for (j = 0; j < end; j++)
                {
                    sum += mtrx[i, j] * (int)txt[j];
                }
                ans[i, 0] = sum;
            }
            Console.Write("Your CipherText is:");
            for (i = 0; i < end; i++)
            {
                char cipher = (char)(((ans[i, 0]) % 26) + 97);
                Console.Write("\t" + cipher);
            }
            Console.ReadKey();
        }
    }
}

Output Window

outputwindow

Hope you like it. Thank you for reading. Have a good day.