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\mode<presentation>{

\begin{frame}<1>[t]

\frametitle{%

  \begin{tabular}{@ {}c@ {}}

  \\[-3mm]

  \LARGE Automata and \\[-2mm] 

  \LARGE Formal Languages (9)\\[3mm] 

  \end{tabular}}

  \normalsize

  \begin{center}

  \begin{tabular}{ll}

  Email:  & christian.urban at kcl.ac.uk\\

  Office: & S1.27 (1st floor Strand Building)\\

  Slides: & KEATS (also home work is there)\\

  \end{tabular}

  \end{center}

\end{frame}}

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\mode<presentation>{

\begin{frame}[c]

\large\bf

Using a compiler, \\how can you mount the\\ perfect attack against a system?

\end{frame}}

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\mode<presentation>{

\begin{frame}[c]

{\large\bf

\begin{enumerate}

\item you can potentially completely take over a target system

\item your attack is (nearly) undetectable

\end{enumerate}

\end{frame}}

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\mode<presentation>{

\begin{frame}[c]

  \begin{center}

  \begin{tikzpicture}[scale=1]

  \onslide<1->{

  \node (A) at (0,0)  [draw=black, rectangle, very thick, minimum height=18mm, minimum width=17mm] {};

  \onslide<2->{

  }

  \end{tikzpicture}

  \end{center}

\end{frame}}

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\mode<presentation>{

\begin{frame}[c]

  \begin{center}

  \begin{tikzpicture}[scale=1]

  \onslide<1->{

  \node (A) at (0,0)  [draw=black, rectangle, very thick, minimum height=18mm, minimum width=14mm] {};

  \node [below right] at (A.north west) {\small V0.01};

  \node [below right] (A1) at (A.south west) {\small Scala};

  \node [below right] (A1) at (A1.south west) {\small\textcolor{gray}{host language}};

  \node [above right] at (A.north west) {my compiler (src)};}

  \onslide<2->{

  \node (B) at (1.8,0)  [draw=black, rectangle, very thick, minimum height=18mm, minimum width=14mm] {};

  \node [below right] at (B.north west) {\small V0.02};

  \node [below right] at (B.south west) {\small Scala};

  \node at (3,0) {\ldots};

  \node (C) at (5,0)  [draw=black, rectangle, very thick, minimum height=18mm, minimum width=14mm] {};

  \node [below right] at (C.north west) {\small V1.00};

  \node [below right] at (C.south west) {\small Scala};}

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  \node [below right] at (G.north west) {\small V1.02};

  \node at (9.8,0) {\ldots};

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  \end{center}

\end{frame}}

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  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

  \mode<presentation>{

  \begin{frame}<1-3>

  \frametitle{\LARGE\begin{tabular}{c}Hacking Compilers 

  \end{tabular}}

  %Why is it so paramount to have a small trusted code base (TCB)?

  \bigskip\bigskip

  \begin{columns}

  \begin{column}{2.7cm}

  \begin{minipage}{2.5cm}%

  \begin{tabular}{c@ {}}

  \includegraphics[scale=0.2]{../pics/ken-thompson.jpg}\\[-1.8mm]

  \footnotesize Ken Thompson\\[-1.8mm]

  \footnotesize Turing Award, 1983\\

  \end{tabular}

  \end{minipage}

  \end{column}

  \begin{column}{9cm}

  \begin{tabular}{l@ {\hspace{1mm}}p{8cm}}

  \myitemi

  & Ken Thompson showed how to hide a Trojan Horse in a 

  compiler \textcolor{red}{without} leaving any traces in the source code.\\[2mm]

  \myitemi

  & No amount of source level verification will protect 

  you from such Thompson-hacks.\\[2mm]

  \myitemi

  & Therefore in safety-critical systems it is important to rely 

  on only a very small TCB.

  \end{tabular}

  \end{column}

  \end{columns}

  \only<2>{

  \begin{textblock}{6}(4,2)

  \begin{tikzpicture}

  \draw (0,0) node[inner sep=3mm,fill=cream, ultra thick, draw=red, rounded corners=2mm] 

  {\normalsize

  \begin{minipage}{8cm}

  \begin{quote}

  \includegraphics[scale=0.05]{../pics/evil.png}

  \begin{enumerate}

  \item[1)] Assume you ship the compiler as binary and also with sources.

  \item[2)] Make the compiler aware when it compiles itself.

  \item[3)] Add the Trojan horse.

  \item[4)] Compile.

  \item[5)] Delete Trojan horse from the sources of the compiler.

  \item[6)] Go on holiday for the rest of your life. ;o)\\[-7mm]\mbox{}

  \end{enumerate}

  \end{quote}

  \end{minipage}};

  \end{tikzpicture}

  \end{textblock}}

  \end{frame}}

  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%     

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\mode<presentation>{

\begin{frame}[c]

\frametitle{\begin{tabular}{c}While-Language\end{tabular}}

\begin{center}

\bl{\begin{tabular}{@{}lcl@{}}

$Stmt$ & $\rightarrow$ &  $\text{skip}$\\

              & $|$ & $Id := AExp$\\

              & $|$ & $\text{if}\; B\!Exp \;\text{then}\; Block \;\text{else}\; Block$\\

              & $|$ & $\text{while}\; B\!Exp \;\text{do}\; Block$\\

$Stmts$ & $\rightarrow$ &  $Stmt \;\text{;}\; Stmts$\\

              & $|$ & $Stmt$\medskip\\

$Block$ & $\rightarrow$ &  $\{ Stmts \}$\\

                & $|$ & $Stmt$\medskip\\

$AExp$ & $\rightarrow$ & \ldots\\

$BExp$ & $\rightarrow$ & \ldots\\

\end{tabular}}

\end{center}

\end{frame}}

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\mode<presentation>{

\begin{frame}[c]

\frametitle{\begin{tabular}{c}Interpreter\end{tabular}}

\begin{center}

\bl{\begin{tabular}{@{}lcl@{}}

$\text{eval}(n, E)$ & $\dn$ & $n$\\

$\text{eval}(x, E)$ & $\dn$ & $E(x)$ \;\;\;\textcolor{black}{lookup \bl{$x$} in \bl{$E$}}\\

$\text{eval}(a_1 + a_2, E)$ & $\dn$ & $\text{eval}(a_1, E) + \text{eval}(a_2, E)$\\

$\text{eval}(a_1 - a_2, E)$ & $\dn$ & $\text{eval}(a_1, E) - \text{eval}(a_2, E)$\\

$\text{eval}(a_1 * a_2, E)$ & $\dn$ & $\text{eval}(a_1, E) * \text{eval}(a_2, E)$\bigskip\\

$\text{eval}(a_1 = a_2, E)$ & $\dn$ & $\text{eval}(a_1, E) = \text{eval}(a_2, E)$\\

$\text{eval}(a_1\,!\!= a_2, E)$ & $\dn$ & $\neg(\text{eval}(a_1, E) = \text{eval}(a_2, E))$\\

$\text{eval}(a_1 < a_2, E)$ & $\dn$ & $\text{eval}(a_1, E) < \text{eval}(a_2, E)$\

\end{tabular}}

\end{center}

\end{frame}}

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\mode<presentation>{

\begin{frame}[c]

\frametitle{\begin{tabular}{c}Interpreter (2)\end{tabular}}

\begin{center}

\bl{\begin{tabular}{@{}lcl@{}}

$\text{eval}(\text{skip}, E)$ & $\dn$ & $E$\\

$\text{eval}(x:=a, E)$ & $\dn$ & \bl{$E(x \mapsto \text{eval}(a, E))$}\\

\multicolumn{3}{@{}l@{}}{$\text{eval}(\text{if}\;b\;\text{then}\;cs_1\;\text{else}\;cs_2 , E) \dn$}\\

\multicolumn{3}{@{}l@{}}{\hspace{2cm}$\text{if}\;\text{eval}(b,E)\;\text{then}\;

\text{eval}(cs_1,E)$}\\

\multicolumn{3}{@{}l@{}}{\hspace{2cm}$\phantom{\text{if}\;\text{eval}(b,E)\;}\text{else}\;\text{eval}(cs_2,E)$}\\

\multicolumn{3}{@{}l@{}}{$\text{eval}(\text{while}\;b\;\text{do}\;cs, E) \dn$}\\

\multicolumn{3}{@{}l@{}}{\hspace{2cm}$\text{if}\;\text{eval}(b,E)$}\\

\multicolumn{3}{@{}l@{}}{\hspace{2cm}$\text{then}\;

\text{eval}(\text{while}\;b\;\text{do}\;cs, \text{eval}(cs,E))$}\\

\multicolumn{3}{@{}l@{}}{\hspace{2cm}$\text{else}\; E$}\\

$\text{eval}(\text{write}\; x, E)$ & $\dn$ & $\{\;\text{println}(E(x))\; ;\;E\;\}$\\

\end{tabular}}

\end{center}

\end{frame}}

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\mode<presentation>{

\begin{frame}[t]