Well, lets be fair here. Saying &quot;Don&#x27;t roll your own encryption&quot; doesn&#x27;t specify &quot;maths&quot; or &quot;applied crypto&quot; (which incidentally covers security&#x2F;auth mechanisms).<p>It&#x27;s a bad idea to roll your own versions of <i>either</i> the maths part <i>or</i> the applied part, so I don&#x27;t think the GP was inaccurate in his statement.