Encode / Decode in asp.net

How to encode the text in asp.net / How to Decode the text in asp.net

<asp:TextBox ID="txtSDate" runat="server" onkeypress="return false;" oncopy="return false;" oncut="return false;" onpaste="return false;" Width="152px"></asp:TextBox>

 public static string base64Decode(string sData)
 {
    try
    {
    System.Text.UTF8Encoding encoder = new System.Text.UTF8Encoding();
System.Text.Decoder utf8Decode = encoder.GetDecoder();
byte[] todecode_byte = Convert.FromBase64String(sData);
int charCount = utf8Decode.GetCharCount(
todecode_byte, 0, todecode_byte.Length);
char[] decoded_char = new char[charCount];

utf8Decode.GetChars(todecode_byte, 0, todecode_byte.Length, decoded_char, 0);
string result = new String(decoded_char);
  return result;
   }
 catch (Exception ex)
 {
     throw new Exception("Error in base64Decode" + ex.Message);
 }
}
public static string base64Encode(string sData)
 {
  try
   {
     byte[] encData_byte = new byte[sData.Length];
 encData_byte = System.Text.Encoding.UTF8.GetBytes(sData);
 string encodedData = Convert.ToBase64String(encData_byte);
 return encodedData;
  }
 catch (Exception ex)
 {
       throw new Exception("Error in base64Encode" + ex.Message);
 }
}
protected void btnSave_Click1(object sender, EventArgs e)
{
   string str = base64Encode(txtEncrypt.Text);
    lblEncrpt.Text = str;
}
protected void btnSave_Click2(object sender, EventArgs e)
{
 string str = base64Decode(txtEncrypt.Text);
 lblEncrpt.Text = str;
}