128-bit encryption

I could find out the way to solve this. You can just create a class file and paste this onto it.

Create a Login Page with the user id and password, a submit button.
On click of a submit button, put the following code...

//Declare this ..
EnDecrypt128 oEnDe = new EnDecrypt128();

string EncryptPwdString;
string DecryptPwdString;
string key="&%&$$@!!#()*^%^%$!@s*#"; // This key can be anything.
EncryptPwdString = oEnDe.EncryptString(txtPwd.Text, key);
DecryptPwdString = oEnDe.DecryptString(EncryptPwdString, key);

// EnDecrypt128.cs -- This is the class name.

public string EncryptString(string InputText, string Password)
{
// "Password" string variable is nothing but the key(your secret key) value which is sent from the front end.
// "InputText" string variable is the actual password sent from the login page.

// We are now going to create an instance of the
// Rihndael class. 
RijndaelManaged RijndaelCipher = new RijndaelManaged();

// First we need to turn the input strings into a byte array.
byte[] PlainText = System.Text.Encoding.Unicode.GetBytes(InputText);

// We are using Salt to make it harder to guess our key
// using a dictionary attack.
byte[] Salt = Encoding.ASCII.GetBytes(Password.Length.ToString());

// The (Secret Key) will be generated from the specified
// password and Salt.

//PasswordDeriveBytes -- It Derives a key from a password
PasswordDeriveBytes SecretKey = new PasswordDeriveBytes(Password, Salt);

// Create a encryptor from the existing SecretKey bytes.
// We use 32 bytes for the secret key
// (the default Rijndael key length is 256 bit = 32 bytes) and
// then 16 bytes for the IV (initialization vector),
// (the default Rijndael IV length is 128 bit = 16 bytes)

ICryptoTransform Encryptor = RijndaelCipher.CreateEncryptor(SecretKey.GetBytes(16), SecretKey.GetBytes(16));

// Create a MemoryStream that is going to hold the encrypted bytes
MemoryStream memoryStream = new MemoryStream();

// Create a CryptoStream through which we are going to be processing our data.
// CryptoStreamMode.Write means that we are going to be writing data
// to the stream and the output will be written in the MemoryStream
// we have provided. (always use write mode for encryption)
CryptoStream cryptoStream = new CryptoStream(memoryStream, Encryptor, CryptoStreamMode.Write);
   
// Start the encryption process.
cryptoStream.Write(PlainText, 0, PlainText.Length);
   
// Finish encrypting.
cryptoStream.FlushFinalBlock();

// Convert our encrypted data from a memoryStream into a byte array.
byte[] CipherBytes = memoryStream.ToArray();

// Close both streams.
memoryStream.Close();
cryptoStream.Close();
    
// Convert encrypted data into a base64-encoded string.
// A common mistake would be to use an Encoding class for that.
// It does not work, because not all byte values can be
// represented by characters. We are going to be using Base64 encoding
// That is designed exactly for what we are trying to do.
string EncryptedData = Convert.ToBase64String(CipherBytes);

// Return encrypted string.
return EncryptedData;
}
--------------------------------------------------------------------

public string DecryptString(string InputText, string Password)
{
RijndaelManaged  RijndaelCipher = new RijndaelManaged();

byte[] EncryptedData = Convert.FromBase64String(InputText);
byte[] Salt = Encoding.ASCII.GetBytes(Password.Length.ToString());
      
PasswordDeriveBytes SecretKey = new PasswordDeriveBytes(Password, Salt);
      
// Create a decryptor from the existing SecretKey bytes.
ICryptoTransform Decryptor = RijndaelCipher.CreateDecryptor(SecretKey.GetBytes(16), SecretKey.GetBytes(16));

MemoryStream  memoryStream = new MemoryStream(EncryptedData);
           
// Create a CryptoStream. (always use Read mode for decryption).
CryptoStream  cryptoStream = new CryptoStream(memoryStream, Decryptor, CryptoStreamMode.Read);

// Since at this point we don't know what the size of decrypted data
// will be, allocate the buffer long enough to hold EncryptedData;
// DecryptedData is never longer than EncryptedData.
byte[] PlainText = new byte[EncryptedData.Length];
       
// Start decrypting.
int DecryptedCount = cryptoStream.Read(PlainText, 0, PlainText.Length);
               
memoryStream.Close();
cryptoStream.Close();
       
// Convert decrypted data into a string.
string DecryptedData = Encoding.Unicode.GetString(PlainText, 0, DecryptedCount);
       
// Return decrypted string.  
return DecryptedData; }

Note: Its taken from some of the article found in google and customised to my requirement.

- Have a nice time...