title: Range of valid character for a base 64 encoding
body: <p>I am interested in the following:<br>
  Is there a list of characters that would <strong>never</strong> occur as part of a base 64 encoded string?<br>
  For example <code>*</code>. I am not sure if this would occur or not. If the original input actually had <code>*</code> as part of it would that be encoded differently?</p>