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

\begin{document}

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\begin{frame}[t]

\frametitle{%

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

  \\

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

\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{A Simple PK Protocol}

\begin{center}

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

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

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

3. & \bl{$A \to B :$} & \bl{$\{A,m\}_{K^{pub}_B}$}\smallskip\\

4. & \bl{$B \to A :$} & \bl{$\{B,m'\}_{K^{pub}_A}$}

\end{tabular}

\end{center}\pause\bigskip

unfortunately there is a simple man-in-the- middle-attack

\end{frame}

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\begin{frame}[c]

\frametitle{A MITM Attack}

\begin{center}

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

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

2. & \bl{$E \to B :$} & \bl{$K^{pub}_E$}\smallskip\\

3. & \bl{$B \to E :$} & \bl{$K^{pub}_B$}\smallskip\\

4. & \bl{$E \to A :$} & \bl{$K^{pub}_E$}\smallskip\\

5. & \bl{$A \to E :$} & \bl{$\{A,m\}_{K^{pub}_E}$}\smallskip\\

6. & \bl{$E \to B :$} & \bl{$\{E,m\}_{K^{pub}_B}$}\smallskip\\

7. & \bl{$B \to E :$} & \bl{$\{B,m'\}_{K^{pub}_E}$}\smallskip\\

8. & \bl{$E \to A :$} & \bl{$\{E,m'\}_{K^{pub}_A}$}

\end{tabular}

\end{center}\pause\medskip

and \bl{$A$} and \bl{$B$} have no chance to detect it

\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}

\end{frame}

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\begin{frame}[c]

\frametitle{Splitting Messages}

\begin{center}

$\underbrace{\texttt{\Grid{0X1peUVTGJK+H70mMjAM8p}}}_{\{A,m\}_{K^{pub}_B}}$

\end{center}

\begin{center}

$\underbrace{\texttt{\Grid{0X1peUVTGJK}}}_{H_1}$\quad

$\underbrace{\texttt{\Grid{+H70mMjAM8p}}}_{H_2}$

\end{center}

\begin{itemize}

\item you can also use the even and odd bytes

\item the point is you cannot decrypt the halves

\end{itemize}

\end{frame}

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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{$\{B,m'\}_{K^{pub}_C} \;\mapsto\; M_1,M_2$}\bigskip\\

\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{center}\pause

\footnotesize

\bl{$m$} = How is your grandmother? \bl{$m'$} = How is the

weather today in London?

\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 what happens if \bl{$m$} and \bl{$m'$} are voice

  messages?\bigskip\pause

\item So \bl{$C$} can either leave the communication unchanged

      (Hellamn-Diffie), or invent a complete new conversation

\end{itemize}

\end{frame}

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\begin{frame}[c]

\begin{itemize}

\item the moral: establishing a secure connection from

      ``zero'' is almost impossible---you need to rely on some

      established trust\medskip

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

      badly, badly realised

\end{itemize}

\end{frame}

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\begin{frame}[c]

\frametitle{Trusted Third Parties}

Simple protocol for establishing a secure connection via a

mutually trusted 3rd party (server):

\begin{center}

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

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

\bl{$S \rightarrow A :$} & \bl{$\{K_{AB}, \{K_{AB}\}_{K_{BS}} \}_{K_{AS}}$}\\

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

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

\end{tabular}

\end{center}

\end{frame}

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\begin{frame}[c]

\frametitle{PKI: The Main Idea}

\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 CA must be trusted by everybody\medskip

\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]

\begin{itemize}

\end{itemize}

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