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\renewcommand{\slidecaption}{APP 03, King's College London, 22 October 2014}

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\begin{document}

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\mode<presentation>{

\begin{frame}<1>[t]

\frametitle{%

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

  \\

  \LARGE Access Control and \\[-3mm] 

  \LARGE Privacy Policies (4)\\[-6mm] 

  \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 home work is there)\\

  \end{tabular}

  \end{center}

\end{frame}}

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\mode<presentation>{

\begin{frame}[c]

\begin{center}

\includegraphics[scale=0.45]{pics/trainwreck.jpg}\\

two weeks ago: buffer overflow attacks

\end{center}

\end{frame}}

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\begin{frame}[fragile]

\frametitle{Buffer Overflows}

\begin{verbatim}

As a proof-of-concept, the following URL allows 

attackers to control the return value saved on 

the stack (the vulnerability is triggered when

executing "/usr/sbin/widget"):

 curl http://<target ip>/post_login.xml?hash=AAA...AAABBBB

The value of the "hash" HTTP GET parameter consists in 

292 occurrences of the 'A' character, followed by four 

occurrences of character 'B'. In our lab setup, characters 

'B' overwrite the saved program counter (%ra).

Discovery date: 06/03/2013

Release date:   02/08/2013

\end{verbatim}

\mbox{}\footnotesize\hfill\url{http://pastebin.com/vbiG42VD}  

\end{frame}

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\begin{frame}[fragile]

\frametitle{Backdoors}

D-Link router flaw lets anyone login through "Joel's Backdoor":\medskip

If you tell your browser to identify itself as Joel's backdoor, instead of (say) 

as Mozilla/5.0 AppleWebKit/536.30.1 Version/6.0.5, you're in without authentication.\medskip

"What is this string," I hear you ask?

You will laugh: it is 

\begin{verbatim}

xmlset_roodkcableoj28840ybtide

\end{verbatim}

\hfill\footnotesize October 15, 2013\\

\hfill\tiny\url{http://www.devttys0.com/2013/10/reverse-engineering-a-d-link-backdoor/}

\end{frame}

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\mode<presentation>{

\begin{frame}[c]

\frametitle{Access Control in Unix}

\begin{itemize}

\item access control provided by the OS

\item authenticate principals (login)

\item mediate access to files, ports, processes according to \alert{roles} (user ids)\\

\item roles get attached with privileges\bigskip\\%

\hspace{8mm}

\begin{tikzpicture}

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

{\begin{minipage}{8cm}

\alert{principle of least privilege:}\\

programs should only have as much privilege as they need 

\end{minipage}};

\end{tikzpicture}

\end{itemize}

\end{frame}}

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\mode<presentation>{

\begin{frame}[c]

\frametitle{Access Control in Unix (2)}

\begin{itemize}

\item the idea is to restrict access to files and therefore lower the consequences of an attack\\[1cm]\mbox{}

\end{itemize}

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\end{textblock}

\end{frame}}

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\newcommand{\bl}[1]{\textcolor{blue}{#1}}  

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\begin{frame}[c]

\frametitle{Access Control}

\begin{itemize}

\item \bl{Discretionary Access Control:}\mbox{}\medskip\\
\small Access to objects (files, directories, devices, etc.) is permitted 

based on user identity. Each object is owned by a user. Owners can 

specify freely (at their discretion) how they want to share their objects 

with other users, by specifying which other users can have which 

form of access to their objects.\medskip

Discretionary access control is implemented on any multi-user OS 

(Unix, Windows NT, etc.).

\end{itemize}

\end{frame}

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\begin{frame}[c]

\frametitle{Access Control}

\begin{itemize}

\item \bl{Mandatory Access Control:}\mbox{}\medskip\\
\small Access to objects is controlled by a system-wide policy, for example 

to prevent certain flows of information. In some forms, the system maintains 

security labels for both objects and subjects (processes, users), based on 

which access is granted or denied. Labels can change as the result of an 

access. Security policies are enforced without the cooperation of users or 

application programs.\medskip

This is implemented today in special military operating system versions

(SELinux).

\end{itemize}

\end{frame}

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\mode<presentation>{

\begin{frame}[c]

\frametitle{Discretionary Access Control}

In its most generic form usually given by an Access Control Matrix 

of the form

\begin{center}

\begin{tabular}{r|c|c|c}

                 & /mail/jane & edit.exe & sendmail \\\hline

jane          & r, w & r, x & r, x\\\hline

john          & $\varnothing$ & r, w, x&  r, x\\\hline

sendmail  & a & $\varnothing$ &  r, x\\

\end{tabular}

\end{center}

access privileges: {\bf r}ead, {\bf w}rite, e{\bf x}ecute, {\bf a}ppend

\end{frame}}

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\begin{frame}[c]

\frametitle{Mandatory Access Control}

\begin{itemize}

\item Restrictions to allowed information flows are not decided at the user’s 

discretion (as with Unix chmod), but instead enforced by system policies.

\item Mandatory access control mechanisms are aimed in particular at 

preventing policy violations by untrusted application software, which 

typically have at least the same access privileges as the invoking user.\medskip

Simple example: Air Gap Security.
Uses completely separate network and computer hardware for different application classes.

\end{itemize}

\end{frame}

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\mode<presentation>{

\begin{frame}[c]

\begin{itemize}

\end{itemize}

\begin{center}

\end{center}

\end{frame}}

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