encode and decode string in C#

string authHeaderValue="hamid123456789"
 byte[] byt = System.Text.Encoding.UTF8.GetBytes(authHeaderValue);

            // thenconvert this byte array to a Base64 string

            authHeaderValue = Convert.ToBase64String(byt);
         
now again get it in its original format
            authHeaderValue = Encoding.Default.GetString(Convert.FromBase64String(authHeaderValue));