Hi Archer.. Here is the answer for your query..

This encode function will encode a string and then convert it into base64 string.
public string Encode(string str)
{
byte[] encbuff = System.Text.Encoding.UTF8.GetBytes(str);
return Convert.ToBase64String(encbuff);
}

The Decode function will retrieve the string from the base64 string.
public string Decode(string str)
{
byte[] decbuff = Convert.FromBase64String(str);
return System.Text.Encoding.UTF8.GetString(decbuff);
}