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\begin{document}

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\begin{frame}[t]

\frametitle{%

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

  \\

  \LARGE Security Engineering (9)\\[-3mm] 

  \end{tabular}}\bigskip\bigskip\bigskip

  \normalsize

  \begin{center}

  \begin{tabular}{ll}

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

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

  Slides: & KEATS (also homework is there)\\

  \end{tabular}

  \end{center}

\end{frame}

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  \begin{frame}[c]

  \begin{center}

  \includegraphics[scale=0.6]{../pics/bridge-limits.png}

  \end{center}

  \end{frame}

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  \begin{frame}[c]

  \frametitle{Old-Fashioned Eng.~vs.~CS}

  \begin{center}

  \begin{tabular}{@{}cc@{}}

  \begin{tabular}{@{}p{5.2cm}} 

  \includegraphics[scale=0.058]{../pics/towerbridge.jpg}\\ 

  {\bf bridges}: \\

  \raggedright\small

  engineers can ``look'' at a bridge and have a pretty good

  intuition about whether it will hold up or not\\ 

  (redundancy; predictive theory)

  \end{tabular} &

  \begin{tabular}{p{5cm}} 

  \includegraphics[scale=0.265]{../pics/code.jpg}\\

  \raggedright

  {\bf code}: \\

  \raggedright\small

  programmers have very little intuition about their code; 

  often it is too expensive to have redundancy;

  not ``continuous'' 

  \end{tabular}

  \end{tabular}

  \end{center}

  \end{frame}

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\begin{frame}[c]

\frametitle{Trusting Computing Base}

When considering whether a system meets some security

objectives, it is important to consider which parts of that

system are trusted in order to meet that objective (TCB).

\bigskip\pause

The smaller the TCB, the less effort it takes to get

some confidence that it is trustworthy, by doing a code 

review or by performing some (penetration) testing.

\bigskip

\footnotesize

CPU, compiler, libraries, OS, NP $\not=$ P,

random number generator, \ldots

\end{frame}

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  \begin{frame}[c]

  \frametitle{Dijkstra on Testing}

  \begin{bubble}[10cm]

  ``Program testing can be a very effective way to show the

  presence of bugs, but it is hopelessly inadequate for showing

  their absence.''

  \end{bubble}\bigskip

  unfortunately attackers exploit bugs (Satan's computer vs 

  Murphy's)

  \end{frame}

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\begin{frame}[c]

\frametitle{\Large Proving Programs to be Correct}

\begin{bubble}[10cm]

\small

{\bf Theorem:} There are infinitely many prime 

numbers.\medskip\\

{\bf Proof} \ldots\\

\end{bubble}\bigskip

similarly\bigskip

\begin{bubble}[10cm]

\small

{\bf Theorem:} The program is doing what 

it is supposed to be doing.\medskip

{\bf Long, long proof} \ldots\\

\end{bubble}\bigskip\medskip

\small This can be a gigantic proof. The only hope is to have

help from the computer. `Program' is here to be understood to be

quite general (protocols, OS, \ldots).

\end{frame}

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  \begin{frame}[c]

  \frametitle{\Large{}Mars Pathfinder Mission 1997}

  \begin{center}

  \includegraphics[scale=0.15]{../pics/marspath1.png}

  \includegraphics[scale=0.16]{../pics/marspath3.png}

  \includegraphics[scale=0.3]{../pics/marsrover.png}

  \end{center}

  \begin{itemize}

  \item despite NASA's famous testing procedures, the lander crashed frequently on Mars

  \item a scheduling algorithm was not used in the OS

  \end{itemize}

  \end{frame}

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

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  \end{tabular}

  \end{textblock}

  \begin{textblock}{0}(2.5,13)%

  \small

  \onslide<3->{

  \begin{bubble}[8cm]%

  Scheduling: You want to avoid that a high 

  priority process is starved indefinitely.

  \end{bubble}}

  \end{textblock}

  \end{frame}

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

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

  \begin{frame}[c]

  \frametitle{\Large Priority Inheritance Scheduling}

  \begin{itemize}

  \item Let a low priority process $L$ temporarily inherit 

    the high priority of $H$ until $L$ leaves the critical 

    section unlocking the resource.\bigskip

  \item Once the resource is unlocked $L$ returns to its original 

    priority level.

  \end{itemize}

  \end{frame}

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   \draw[fill, blue!50] (1,0) rectangle (3,0.6);

    \draw[fill, blue!50] (3,3) rectangle (3.5,3.6);