using System;

using System.Text;

​

public class Affine

{

    private string _alpha;

    private int _m, _s, _mod;

    public Affine(int m, int s, string alpha)

    {

        this._m = m;

        this._s = s;

        this._mod = alpha.Length;

        this._alpha = alpha;

    }

​

    public string Encrypt(string text)

    {

        if (string.IsNullOrWhiteSpace(text))

            throw new Exception("Cannot encrypt an empty string you silly fool!");

        var textArray = text.ToCharArray();

        var cipher = new StringBuilder();

        foreach (var c in textArray)

        {

            var v = (((this._alpha.IndexOf(c) * this._m) + this._s) % _mod);

            cipher.Append(this._alpha[v]);

        }

​

        return cipher.ToString();

    }

    public string Decrypt(string text)

    {

        if (string.IsNullOrWhiteSpace(text))

            throw new Exception("Cannot encrypt an empty string you silly fool!");

        var textArray = text.ToCharArray();

        var plain = new StringBuilder();

        foreach (var c in textArray)

        {

            var v = (((this._alpha.IndexOf(c) * this._m) + this._s) % _mod);

            plain.Append(this._alpha[v]);

        }

​

        return plain.ToString();

    }

}

​

//using System.Linq;

public class Program

{

    static string atoz = "abcdefghijklmnopqrstuvwxyz";

    static string plainText = "howareyou";

    static char[] plain = plainText.ToCharArray();

    public static void Main()

    {

        var affine = new Affine(5, 7, "abcdefghijklmnopqrstuvwxyz");

        Console.WriteLine(affine.Encrypt("howareyou"));

        var encrypted = string.Empty;

        var decrypted = string.Empty;

        foreach (var c in plain)

        {

            var v = atoz.IndexOf(c);

            var e = encrypt(v);

            var d = decrypt(e);

            Console.WriteLine("---------------------------------");

            Console.WriteLine("Original:  " + c);

            Console.WriteLine("Map:       " + v);

            Console.WriteLine("Encrypted: " + atoz[e]);

            Console.WriteLine("Decrypted: " + atoz[d]);

            encrypted += atoz[e];

            decrypted += atoz[d];

        }

​

        Console.WriteLine("---------------------------------");

        Console.WriteLine("Encrypted: " + encrypted);

        Console.WriteLine("Decrypted: " + decrypted);

    }

​

    public static int encrypt(int c)

    {

        return (((c * 5) + 7) % 26);

    }

​

    public static int decrypt(int c)

    {

        var x = (((c + -7) * 21) % 26);

        if (x < 0)

            x = 26 + x;

        return x;

    }

}