--- a/hws/hw06.tex	Thu Oct 22 20:19:27 2015 +0100
+++ b/hws/hw06.tex	Sun Oct 25 23:34:04 2015 +0000
@@ -9,6 +9,16 @@
 \HEADER
 
 \begin{enumerate}
+\item Explain briefly the purpose of the certification authority in
+the public-private key encryption scheme.
+
+\item Explain briefly what is meant by a certification authority
+  becoming ``too big to fail'' when it has issued a large number 
+  of certificates.
+
+\item In which situations does it make sense to install
+      invalid (self-signed) certificates?
+
 \item Zero-knowledge protocols depend on three main properties called
   completeness, soundness and zero-knowledge.  Explain what they mean?