Hello Guys,
 
I have sample code here on how to create a simple encryption and decryption on Silverlight.
First, I created a PASSWORD from SL Controls. A Three Button for encryption, decryption, clear.
A one textblock and one textbox.
 
Second, I created a simple function for Encryption and Decryption and variables.
        
        byte[] _encryted;
        byte[] _decryted;
        string s;
 
        private string EncrytedString(string str)
        {
            _encryted = System.Text.Encoding.Unicode.GetBytes(str);
            s = Convert.ToBase64String(_encryted);
            return s;
        }
 
        private string DecrytedString(string str)
        {
            _decryted = Convert.FromBase64String(str);
s = System.Text.Encoding.Unicode.GetString(_decryted, 0,  _decryted.ToArray().Length);
            return s;
        }
 
 
Now the snippets.
 
            //For the Encryption Button
        private void btnEncrypt_Click(object sender, RoutedEventArgs e)
        {
            if (passwordBox1.Password == string.Empty)
            {
                MessageBox.Show("Please Enter your Password");
                passwordBox1.Focus();
            }
            else
            {
                btnDecrypt.IsEnabled = true;
                string s = EncrytedString(passwordBox1.Password);
                txtEncrypted.Text = s;
            }
 
        }
 
           //For the Decryption Button
        private void btnDecrypt_Click(object sender, RoutedEventArgs e)
        {
            string s;
            s = DecrytedString(txtEncrypted.Text);
            MessageBox.Show(s);
        }
 
       //For the Clear Button
        private void btnClear_Click(object sender, RoutedEventArgs e)
        {
            txtEncrypted.Text = string.Empty;
            passwordBox1.Password = string.Empty;
            passwordBox1.Focus();
            btnDecrypt.IsEnabled = false;
        }