
diff -r 64e62d636737 -r fa151c0a3cf4 hws/hw05.tex
--- a/hws/hw05.tex	Sun Oct 19 16:44:31 2014 +0100
+++ b/hws/hw05.tex	Tue Oct 21 02:35:06 2014 +0100
@@ -22,60 +22,18 @@
 intercepting all messages for $B$ and make $A$ decrypt her own challenges.
 
 
-\item Access control is about deciding whether a principal that
-issues a request should be trusted on this request. Explain
-how such decision problems can be solved by using logic.
-
-\item The informal meaning of the formula $P\;\textit{controls}\;F$ is 
-`$P$ is entitled to do $F$'. Give a definition for this formula in terms 
-of $\textit{says}$. 
+\item Before starting a TCP connection, client and servers
+perform a three-way handshake:
 
-\item Explain what is meant by a {\it derived} inference rule.
-
-
-\item Give a justification for the derived rule
 \begin{center}
-\begin{tabular}{c}
-$\Gamma \vdash P\;\textit{controls}\;F$ \hspace{4mm} $\Gamma \vdash P\;\textit{says}\;F$\\\hline
-$\Gamma \vdash F$
+\begin{tabular}{rl}
+$A \rightarrow S$: & SYN\\
+$S \rightarrow A$: & SYN-ACK\\
+$A \rightarrow S$: & ACK\\
 \end{tabular}
 \end{center}
 
-%\item Give a justification for the derived rule
-%\begin{center}
-%\begin{tabular}{c}
-%$\Gamma \vdash P\;\mapsto\;Q$ \hspace{4mm} $\Gamma \vdash P\;\textit{says}\;F$\\\hline
-%$\Gamma \vdash Q\;\textit{says}\;F$
-%\end{tabular}
-%\end{center}
-
-%\item Model formally the situation that a customer has bought a ticket and requests to see a
-%movie. For this suppose three principals, {\it Ticket}, {\it Customer} and {\it Cinema},
-%and suppose an authorization 
-%\begin{center}
-%$\textit{Permitted}(\textit{Customer}, \textit{sees\_movie})$.
-%\end{center}
-%Using access-control logic, give formulas for a {\it Customer}'s access
-%request, an access-control policy of the {\it Cinema}, a trust assumption
-%and a ticket rule.
-
-\item Assume $\Gamma$ is a set consisting of the three formulas:
-\begin{center}
-\begin{tabular}{l}
-\\
-$(\textit{Admin}\;\textit{says}\;\textit{del\_file})\;\Rightarrow\;\textit{del\_file}$\\
-$\textit{Admin}\;\textit{says}\;((\textit{Alice}\;\textit{says}\;\textit{del\_file})
-\Rightarrow \textit{del\_file})$\\
-$\textit{Alice}\;\textit{says}\;\textit{del\_file}$\\
-\\
-\end{tabular}
-\end{center}
-
-Give a proof of the judgement
-\begin{center}
-$\Gamma \vdash \textit{del\_file}$
-\end{center}
-
+How can this protocol be abused causing trouble on the server?
 
 \end{enumerate}
 \end{document}




