how can i make program that encrypt and decrypt by using monoalphabatic methodolgy

encrypt and decryption is based on different kind of algorithms. check out this example if its be help full to you......

Firstly add namespace to your class file

using System.Security.Cryptography;

private static byte[] key = { };
private static byte[] IV = { 0x12, 0x34, 0x56, 0x78, 0x90, 0xAB, 0xCD, 0xEF };
private static string EncryptionKey = "!5623a#de";

public static string Decrypt(string Input)
{
Byte[] inputByteArray = new Byte[Input.Length];
try
{
key = System.Text.Encoding.UTF8.GetBytes(EncryptionKey.Substring(0, 8));
DESCryptoServiceProvider des = new DESCryptoServiceProvider();
inputByteArray = Convert.FromBase64String(Input);
MemoryStream ms = new MemoryStream();
CryptoStream cs = new CryptoStream(ms, des.CreateDecryptor(key, IV), CryptoStreamMode.Write);
cs.Write(inputByteArray, 0, inputByteArray.Length);
cs.FlushFinalBlock();

Encoding encoding = Encoding.UTF8;
return encoding.GetString(ms.ToArray());

}
catch (Exception ex)
{
return "";
}

}

public static string Encrypt(string Input)
{
try
{
key = System.Text.Encoding.UTF8.GetBytes(EncryptionKey.Substring(0, 8));
DESCryptoServiceProvider des = new DESCryptoServiceProvider();
Byte[] inputByteArray = Encoding.UTF8.GetBytes(Input);
MemoryStream ms = new MemoryStream();
CryptoStream cs = new CryptoStream(ms, des.CreateEncryptor(key, IV), CryptoStreamMode.Write);
cs.Write(inputByteArray, 0, inputByteArray.Length);
cs.FlushFinalBlock();
return Convert.ToBase64String(ms.ToArray());
}
catch (Exception ex)
{
return "";
}
}