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


\begin{document}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[t]
\frametitle{%
  \begin{tabular}{@ {}c@ {}}
  \\
  \LARGE Security Engineering (6)\\[-3mm] 
  \end{tabular}}\bigskip\bigskip\bigskip

  \normalsize
  \begin{center}
  \begin{tabular}{ll}
  Email:  & christian.urban at kcl.ac.uk\\
  Office: & N7.07 (North Wing, Bush House)\\
  Slides: & KEATS (also homework is there)\\
  \end{tabular}
  \end{center}

\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%     

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[c]
\frametitle{Topical Slide}

\begin{itemize}
\item DoS attack agains some US webpages (hijacked IoT devives, like
  cameras,\ldots)

\item funny cow attack (privilege escalation attack) 
\end{itemize}
  
\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%  


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\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}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   

 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\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 certificates are time limited, and can be revoked

\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}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[c]
\frametitle{PKI: Chains of Trust}

\begin{center}
  \begin{tikzpicture}[scale=1,
                      node/.style={
                      rectangle,rounded corners=3mm,
                      very thick,draw=black!50,minimum height=18mm, minimum width=23mm,
                      top color=white,bottom color=black!20}]

  \node (A) at (0,0)  [node] {};
  \node [below right] at (A.north west) 
  {\small\begin{tabular}{@{}l}CA\\Root Cert.\end{tabular}};

  \node (B) at (4,0)  [node] {};
  \node [below right=1mm] at (B.north west) 
 {\mbox{}\hspace{-1mm}\small
  \begin{tabular}{@{}l}Subordinate\\ CA\end{tabular}};

  \node (C) at (8,0)  [node] {};
  \node [below right] at (C.north west) 
  {\small\begin{tabular}{@{}l}Server\\ Bank.com\end{tabular}};

  \draw [->,line width=4mm] (A) -- (B); 
  \draw [->,line width=4mm] (B) -- (C); 
  
  \node (D) at (6,-3)  [node] {};
  \node [below right] at (D.north west) 
  {\small\begin{tabular}{@{}l}Browser\\ Root Store\end{tabular}};

  \node (E) at (2,-3)  [node] {};
  \node [below right] at (E.north west) 
  {\small\begin{tabular}{@{}l}Browser\\ Vendor\end{tabular}};

  \draw [->,line width=4mm] (E) -- (D); 
  \end{tikzpicture}
\end{center}

\begin{itemize}
\item CAs make almost no money anymore, because of stiff
  competition
\item browser companies are not really interested in security;
  only in market share
\end{itemize}
  
\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%  

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[c]
\frametitle{PKI: Weaknesses}

CAs just cannot win (make any profit):\medskip

\begin{itemize}
\item there are hundreds of CAs, which issue millions of
      certificates and the error rate is small

\item users (servers) do not want to pay or pay as little as
      possible\bigskip

\item a CA can issue a certificate for any domain not needing
      any permission (CAs are meant to undergo audits,
      but\ldots DigiNotar)
      
\item if a CA has issued many certificates, it ``becomes too
      big to fail'' 
  
\item Can we be sure CAs are not just frontends of some 
      government organisation?  
       
\end{itemize}

\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[c]
\frametitle{PKI: Weaknesses}

\begin{itemize}

\item many certificates are issued via Whois, whether you own
      the domain\ldots if you hijacked a domain, it is easy to
      obtain certificates\medskip

\item the revocation mechanism does not work (Chrome has given
      up on general revocation lists)\medskip

\item lax approach to validation of certificates 
  (Have you ever bypassed certification warnings?)\medskip

\item sometimes you want to actually install invalid
      certificates (self-signed)
   
\end{itemize}

\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[c]
\frametitle{PKI: Attacks}

\begin{itemize}

\item Go directly after root certificates 
  \begin{itemize}
  \item governments can demand private keys\smallskip
  \item 10 years ago it was estimated that breaking a 1024 bit
        key takes one year and costs 10 - 30 Mio \$; this is now
        reduced to 1 Mio \$
   \end{itemize} 

\item Go after buggy implementations of certificate
      validation\smallskip

\item Social Engineering 
  \begin{itemize}
    \item in 2001 somebody pretended to be 
    from Microsoft and asked for two code-signing 
    certificates
    \end{itemize}\bigskip
\end{itemize}

\small The eco-system is completely broken (it relies on
thousands of entities to do the right thing). Maybe DNSSEC
where keys can be attached to domain names is a way out.

\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[c]
\frametitle{Real Attacks}

\begin{itemize}

\item In 2011, DigiNotar (Dutch company) was the first CA that
      got compromised comprehensively, and where many
      fraudulent certificates were issued to the wild. It
      included approximately 300,000 IP addresses, mostly
      located in Iran. The attackers (in Iran?) were likely
      interested ``only'' in collecting gmail passwords.\medskip

\item The Flame malware piggy-bagged on this attack by
      advertising malicious Windows updates to some targeted
      systems (mostly in Iran, Israel, Sudan).

\end{itemize}

\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[c]
\frametitle{PKI is Broken}

\begin{itemize}

\item PKI and certificates are meant to protect you against
      MITM attacks, but if the attack occurs your are 
      presented with a warning and you need to decide whether
      you are under attack.\medskip

\item Webcontent gets often loaded from 3rd-party servers,
      which might not be secured\medskip
     
\item Misaligned incentives: browser vendors are not
      interested in breaking webpages with invalid
      certificates     

\end{itemize}

\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[c]

Why are there so many invalid certificates?\bigskip

\begin{itemize}

\item insufficient name coverage (www.example.com should
include example.com)

\item IoT: many appliances have web-based admin interfaces; 
  the manufacturer cannot know under which IP and domain name
  the appliances are run (so cannot install a valid certificate)

\item expired certificates, or incomplete chains of trust
      (servers are supposed to supply them)

\end{itemize}

\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   

%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%\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}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%\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}
%
%\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%\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}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%\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}
%
%\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\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}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[c]
\frametitle{Security Engineering}
  
  \begin{center}
  \begin{tabular}{cc}
  \raisebox{-0.8mm}{\includegraphics[scale=0.28]{../pics/flight.jpg}} &
  \includegraphics[scale=0.31]{../pics/airbus.jpg}\\
  \small Wright brothers, 1901 & \small Airbus, 2005 \\ 
  \end{tabular}
  \end{center}

  \end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[c]
\frametitle{1st Lecture}

\begin{itemize}
\item chip-and-pin, banks vs.~customers
\begin{quote}\small\rm
 the one who can improve security should also be 
 liable for the losses 
\end{quote}\pause\bigskip

\item hashes and salts to guarantee data integrity\medskip
\item storing passwords (you should know the difference between
brute force attacks and dictionary attacks; how do salts help?)
\end{itemize}

\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%  

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[c]
\frametitle{1st Lecture: Cookies}

\begin{itemize}
\item good uses of cookies?\medskip

\item bad uses of cookies: snooping, tracking, profiling\ldots
      the ``disadvantage'' is that the user is in
      \alert{control}, because you can delete them 
          
          \begin{center} ``Please track me using cookies.''
          \end{center}\bigskip\pause
                 
\item fingerprinting beyond browser cookies
  \begin{quote}\small\rm
  Pixel Perfect: Fingerprinting Canvas in HTML5\\ 
  (a research paper from 2012)\\
  \footnotesize
  \url{http://cseweb.ucsd.edu/~hovav/papers/ms12.html}      
  \end{quote}      
\end{itemize}

\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%  

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[c]
\frametitle{1st Lecture: Cookies}

\begin{itemize}
\item a bit of JavaScript and HTML5 + canvas\medskip
\begin{center}
\begin{tabular}{cc}
Firefox & Safari\\
\includegraphics[scale=0.31]{../pics/firefox1.png} &
\includegraphics[scale=0.31]{../pics/safari1.png} \\
\tiny
\pcode{55b2257ad0f20ecbf927fb66a15c61981f7ed8fc} &
\tiny
\pcode{17bc79f8111e345f572a4f87d6cd780b445625d3}
\end{tabular}
\end{center}\bigskip

\item\small no actual drawing needed\pause
\item\small in May 2014 a crawl of 100,000 popular 
webpages revealed 5.5\% already use canvas 
fingerprinting\smallskip
\begin{center}\scriptsize
\url{https://securehomes.esat.kuleuven.be/~gacar/persistent/the_web_never_forgets.pdf}
\end{center}
\end{itemize}

\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%  

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[c]
\frametitle{1st Lecture: Cookies}

Remember the small web-app I showed you where a cookie 
protected a counter?\bigskip 

\begin{itemize}
\item NYT, the cookie looks the ``resource'' - harm\medskip
\item imaginary discount unlocked by cookie - no harm
\end{itemize}

\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%  


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[t]
\frametitle{2nd Lecture: E-Voting}

Where are paper ballots better than voice voting?\bigskip

\begin{itemize}
\item Integrity 
\item \alert{Ballot Secrecy}
\item Voter Authentication
\item Enfranchisement
\item Availability
\end{itemize}

\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[t]
\frametitle{2nd Lecture: E-Voting}

\begin{itemize}
\item recently an Australian parliamentary committee 
found: e-voting is highly vulnerable to hacking and Australia 
will not use it any time soon\bigskip\pause
\item Alex Halderman, Washington D.C.~hack
\begin{center}
\scriptsize
\url{https://jhalderm.com/pub/papers/dcvoting-fc12.pdf}
\end{center}\medskip

\item PDF-ballot tampering at the wireless router (the modification 
is nearly undetectable and leaves no traces; MITM attack with firmware 
updating)
\begin{center}
\scriptsize
\url{http://galois.com/wp-content/uploads/2014/11/technical-hack-a-pdf.pdf}
\end{center}

\end{itemize}

\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\tikzset{alt/.code args={<#1>#2#3#4}{%
  \alt<#1>{\pgfkeysalso{#2}}{\pgfkeysalso{#3}} % \pgfkeysalso doesn't change the path
}}

\begin{frame}[t]
\frametitle{\begin{tabular}{c}3rd Lecture:\\ Buffer Overflow Attacks\end{tabular}}

\begin{itemize}
\item the problem arises from the way C/C++ organises its function calls\\[-8mm]\mbox{}
\end{itemize}

\begin{center}
\begin{tikzpicture}[scale=1]
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%\draw[black!10,thick,step=10mm] (0,0) grid (9,4);

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\end{tikzpicture}
\end{center}

\end{frame}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[t]

\begin{center}
\begin{tikzpicture}[scale=1]
%\draw[black!10,step=2mm] (0,0) grid (9,4);
%\draw[black!10,thick,step=10mm] (0,0) grid (9,4);

\node at (0.5,4.5) {\small\begin{tabular}{l}main\\[-2mm] prog.\end{tabular}};
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\end{tikzpicture}
\end{center}

\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[t]
\frametitle{\begin{tabular}{c}3rd Lecture:\\[-3mm] 
Buffer Overflow Attacks\end{tabular}}

US National Vulnerability Database\\ 
\small(636 out of 6675 in 2014)

\begin{center}
\begin{tikzpicture}
\begin{axis}[
    xlabel={year},
    ylabel={\% of total attacks},
    ylabel style={yshift=0em},
    enlargelimits=false,
    xtick={1997,1999,...,2015},
    xmin=1996.5,
    xmax=2016,
    ymax=21,
    ytick={0,5,...,20},
    scaled ticks=false,
    axis lines=left,
    width=11cm,
    height=5cm,
    ybar,
    nodes near coords=
     {\footnotesize
      $\pgfmathprintnumber[fixed,fixed zerofill,precision=1,use comma]{\pgfkeysvalueof{/data point/y}}$},
    x tick label style={font=\scriptsize,/pgf/number format/1000 sep={}}]
\addplot
  table [x=Year,y=Percentage] {../handouts/bufferoverflows.data};
\end{axis}
\end{tikzpicture}
\end{center}

\scriptsize
\url{http://web.nvd.nist.gov/view/vuln/statistics}
\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[t]
\frametitle{\begin{tabular}{c}4th Lecture:\\ Unix Access Control\end{tabular}}

\begin{itemize}
\item privileges are specified by file access permissions (``everything is a file'') 
\end{itemize}\medskip

\begin{center}
  \begin{tikzpicture}[scale=1]
  
  \draw[line width=1mm] (-.3, 0) rectangle (1.5,2);
  \draw (4.7,1) node {Internet};
  \draw (-2.7,1.7) node {\footnotesize Application};
  \draw (0.6,1.7) node {\footnotesize Interface};
  \draw (0.6,-0.4) node {\footnotesize \begin{tabular}{c}unprivileged\\[-1mm] process\end{tabular}};
  \draw (-2.7,-0.4) node {\footnotesize \begin{tabular}{c}privileged\\[-1mm] process\end{tabular}};
  
  \draw[line width=1mm] (-1.8, 0) rectangle (-3.6,2);

  \draw[white] (1.7,1) node (X) {};
  \draw[white] (3.7,1) node (Y) {};
  \draw[red, <->, line width = 2mm] (X) -- (Y);
 
  \draw[red, <->, line width = 1mm] (-0.6,1) -- (-1.6,1);
  \end{tikzpicture}
\end{center}

\begin{itemize}
\item the idea is to make the attack surface smaller and 
mitigate the consequences of an attack
\end{itemize}

\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[fragile,t]
\frametitle{\begin{tabular}{c}4th Lecture:\\ Unix Access Control\end{tabular}}

\begin{itemize}
\item when a file with setuid is executed, the resulting process will assume the 
UID given to the owner of the file
\end{itemize}

\footnotesize\tt
\begin{center}
\begin{verbatim}
$ ls -ld . * */*
drwxr-xr-x 1 ping staff  32768 Apr  2 2010 .
-rw----r-- 1 ping students  31359 Jul 24 2011 manual.txt
-r--rw--w- 1 bob students    4359 Jul 24 2011 report.txt
-rwsr--r-x 1 bob students  141359 Jun  1 2013 microedit
dr--r-xr-x 1 bob staff      32768 Jul 23 2011 src
-rw-r--r-- 1 bob staff      81359 Feb 28 2012 src/code.c
-r--rw---- 1 emma students    959 Jan 23 2012 src/code.h
\end{verbatim}
\end{center}


\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%  

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[t]
\frametitle{\begin{tabular}{c}4th Lecture:\\ Unix Access Control\end{tabular}}

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\item Alice wants to have her files readable, 
\alert{except} for her office mates.\bigskip

\item make sure you understand the setuid and setgid bits; 
  why are they necessary for login and passwd
\end{itemize}


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