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\renewcommand{\slidecaption}{SEN 05, King's College London}

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\frametitle{%

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

  \\

  \LARGE Security Engineering (5)\\[-3mm] 

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  \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}

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\begin{frame}[c]

\frametitle{Problems with Key Fobs}

\begin{columns}

\begin{column}[T]{4cm}

\includegraphics[scale=0.4]{../pics/car-standard.jpg}

\end{column}

\begin{column}[T]{6cm}\small 

Circumventing the ignition protection:

\begin{itemize}

\item either dismantling Megamos crypto,

\item or use the diagnostic port to program 

  blank keys 

\end{itemize}

\hspace{14mm}

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

\end{column}

\end{columns}

\end{frame}

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\begin{frame}[c]

\frametitle{Protocols}

\begin{center}

\includegraphics[scale=0.11]{../pics/keyfob.jpg}

\quad

\includegraphics[scale=0.232]{../pics/starbucks.jpg}

\end{center}

\begin{itemize}

\item The point is that we have no control over the network

\item We want to avoid that a message exchange (a protocol) can

be attacked without detection

\end{itemize}

\end{frame}

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\begin{frame}[c]

\frametitle{G20 Summit in 2009}

\begin{center}

\includegraphics[scale=0.1]{../pics/snowden.jpg}

\end{center}

\small

\begin{itemize}

\item Snowden documents reveal ``that during G20

      meetings\dots{}GCHQ used 

      `ground-breaking intelligence capabilities' to intercept

      the communications of visiting delegations. This

      included setting up internet cafes where they used an

      email interception program and key-logging software to

      spy on delegates' use of computers\ldots''

\item ``The G20 spying appears to have been organised for the

      more mundane purpose of securing an advantage in

      meetings.'' 

\end{itemize}

\end{frame}

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\begin{frame}[c]

\frametitle{Interlock Protocol}

The interlock protocol (``best bet'' against MITM):

\begin{center}

\begin{tabular}{ll@{\hspace{2mm}}l}

1. & \bl{$A \to B :$} & \bl{$K^{pub}_A$}\\

2. & \bl{$B \to A :$} & \bl{$K^{pub}_B$}\\

3. & & \bl{$\{A,m\}_{K^{pub}_B} \;\mapsto\; H_1,H_2$}\\

   & & \bl{$\{B,m'\}_{K^{pub}_A} \;\mapsto\; M_1,M_2$}\\

4. & \bl{$A \to B :$} & \bl{$H_1$}\\

5. & \bl{$B \to A :$} & \bl{$\{H_1, M_1\}_{K^{pub}_A}$}\\

6. & \bl{$A \to B :$} & \bl{$\{H_2, M_1\}_{K^{pub}_B}$}\\

7. & \bl{$B \to A :$} & \bl{$M_2$}

\end{tabular}

\end{center}

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\begin{frame}[c]

\begin{center}

\begin{tabular}{l@{\hspace{9mm}}l}

\begin{tabular}[t]{@{}l@{}}

\bl{$A \to C : K^{pub}_A$}\\

\bl{$C \to B : K^{pub}_C$}\\

\bl{$B \to C : K^{pub}_B$}\\

\bl{$C \to A : K^{pub}_C$}\medskip\\

\bl{$\{A,m\}_{K^{pub}_C} \;\mapsto\; H_1,H_2$}\\

\bl{$\{C,a\}_{K^{pub}_B} \;\mapsto\; C_1,C_2$}\\

\bl{$\{C,b\}_{K^{pub}_A} \;\mapsto\; D_1,D_2$}

\end{tabular} &

\begin{tabular}[t]{@{}l@{}}

\bl{$A \to C : H_1$}\\

\bl{$C \to B : C_1$}\\

\bl{$B \to C : \{C_1, M_1\}_{K^{pub}_C}$}\\

\bl{$C \to A : \{H_1, D_1\}_{K^{pub}_A}$}\\

\bl{$A \to C : \{H_2, D_1\}_{K^{pub}_C}$}\\

\bl{$C \to B : \{C_2, M_1\}_{K^{pub}_B}$}\\

\bl{$B \to C : M_2$}\\

\bl{$C \to A : D_2$}

\end{tabular}

\end{tabular}

\end{frame}

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\begin{frame}[c]

\begin{itemize}

\item you have to ask something that cannot imitated 

  (requires \bl{$A$} and \bl{$B$} know each other)

\item that is why we rely on certificates, which however are

\end{itemize}

\end{frame}

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\begin{frame}[c]

\begin{center}

\begin{tabular}{r@ {\hspace{1mm}}l}

\bl{$A \rightarrow S :$} & \bl{$A, B$}\\

\bl{$A \rightarrow B :$} & \bl{$\{K_{AB}\}_{K_{BS}} $}\\

\bl{$A \rightarrow B :$} & \bl{$\{m\}_{K_{AB}}$}\\

\end{tabular}

\end{center}

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\begin{frame}[c]

\begin{itemize}

\item the idea is to have a certificate authority (CA)

\item you go to the CA to identify yourself

\item CA: ``I, the CA, have verified that public key 

  \bl{$P^{pub}_{Bob}$} belongs to Bob''\bigskip

\item What happens if CA issues a false certificate? Who pays in case of loss? (VeriSign 

explicitly limits liability to \$100.)

\end{itemize}

\end{frame}

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\begin{frame}[c]

\frametitle{Best Practices}

{\bf Principle 1:} Every message should say what it means: the

interpretation of a message should not depend on the

context.\bigskip\pause

{\bf Principle 2:} If the identity of a principal is essential

to the meaning of a message, it is prudent to mention the

principal’s name explicitly in the message (though

difficult).\bigskip

\end{frame}

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\begin{frame}[c]

\frametitle{Best Practices}

{\bf Principle 3:} Be clear about why encryption is being

done. Encryption is not wholly cheap, and not asking precisely

why it is being done can lead to redundancy. Encryption is not

synonymous with security.

\small

\begin{center}

Possible Uses of Encryption

\begin{itemize}

\item Preservation of confidentiality: \bl{$\{X\}_K$} only those that have \bl{$K$} may recover \bl{$X$}.
\item Guarantee authenticity: The partner is indeed some particular principal.
\item Guarantee confidentiality and authenticity: binds two parts of a message --- 

\bl{$\{X,Y\}_K$} is not the same as \bl{$\{X\}_K$} and \bl{$\{Y\}_K$}.

\end{itemize}

\end{center}

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\begin{frame}[c]

\frametitle{Best Practices}

{\bf Principle 4:} The protocol designers should know which

trust relations their protocol depends on, and why the

dependence is necessary. The reasons for particular trust

relations being acceptable should be explicit though they will

be founded on judgment and policy rather than on

logic.\bigskip

Example Certification Authorities: CAs are trusted to certify

a key only after proper steps have been taken to identify the

principal that owns it.

\end{frame}

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\begin{frame}[c]

\frametitle{Formal Methods}

Ross Anderson about the use of Logic:\bigskip

\begin{quote}

Formal methods can be an excellent way of finding 

bugs in security protocol designs as they force the designer 

to make everything explicit and thus confront difficult design 

choices that might otherwise be fudged. 

\end{quote}

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\begin{frame}[c]

\frametitle{Mid-Term}

\begin{itemize}

\item homework, handouts, programs\ldots

\end{itemize}\bigskip\bigskip\bigskip

\begin{center}

{\huge\bf\alert{Any Questions?}}

\end{center}

\end{frame}

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\end{document}

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