--- a/slides/slides04.tex	Sun Oct 19 16:44:31 2014 +0100
+++ b/slides/slides04.tex	Tue Oct 21 02:35:06 2014 +0100
@@ -885,6 +885,23 @@
 
 \end{frame}}
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\mode<presentation>{
+\begin{frame}[c]
+\frametitle{Public-Key Infrastructure}
+
+\begin{itemize}
+\item the idea is to have a certificate authority (CA)
+\item you go to the CA to identify yourself
+\item CA: ``I, the CA, have verified that public key \bl{$P^{pub}_{Bob}$} belongs to Bob''\bigskip
+\item CA must be trusted by everybody
+\item What happens if CA issues a false certificate? Who pays in case of loss? (VeriSign 
+explicitly limits liability to \$100.)
+\end{itemize}
+
+\end{frame}}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%  
   
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \mode<presentation>{