Binary file hws/hw06.pdf has changed

--- 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?
 

Binary file hws/hw07.pdf has changed

--- a/hws/hw07.tex	Thu Oct 22 20:19:27 2015 +0100
+++ b/hws/hw07.tex	Sun Oct 25 23:34:04 2015 +0000
@@ -10,6 +10,8 @@
 
 \item What is meant by the notion \emph{forward privacy}?
 
+\item What is a \emph{re-identification attack}?
+
 \item Imagine you have an completely `innocent' email message,
       like birthday wishes to your grandmother? Why should you
       still encrypt this message and your grandmother take the

Binary file hws/hw08.pdf has changed

--- a/hws/hw08.tex	Thu Oct 22 20:19:27 2015 +0100
+++ b/hws/hw08.tex	Sun Oct 25 23:34:04 2015 +0000
@@ -6,19 +6,22 @@
 \section*{Homework 8}
 
 \begin{enumerate}
-\item (\textbf{Optional}) How can the hardness of the
-      proof-of-work puzzles in Bitcoins be adjusted? What is
-      parameter that determines how the hardness is adjusted?
+\item How can the hardness of the proof-of-work puzzles in
+      Bitcoins be adjusted? What is parameter that determines
+      how the hardness is adjusted?
 
-\item (\textbf{Optional}) What is the main data that is stored
-      in Bitcoin's blockchain? 
+\item What is the main data that is stored in Bitcoin's
+      blockchain? 
       
-\item (\textbf{Optional}) What is is the purpose of the
-      proof-of-work puzzle in Bitcoins?      
+\item What is is the purpose of the proof-of-work puzzle in
+      Bitcoins?      
 
-\item (\textbf{Optional}) The department has large labs full
-      of computers that are pretty much idle over night. Why
-      is it a bad idea to let them mine for Bitcoins?
+\item The department has large labs full of computers that are
+      pretty much idle over night. Why is it a bad idea to let
+      them mine for Bitcoins?
+
+\item Is it possible that Bitcoins can get lost (be
+      unretrievable)?
 
 \end{enumerate}
 \end{document}