
diff -r 279fa5a06231 -r 6f884231ca57 slides/slides09.tex
--- a/slides/slides09.tex	Mon Dec 02 10:04:40 2013 +0000
+++ b/slides/slides09.tex	Tue Dec 03 03:20:42 2013 +0000
@@ -38,60 +38,8 @@
 \renewcommand{\isasymdots}{\isamath{...}}
 \renewcommand{\isasymbullet}{\act}
 
-
-
-\definecolor{javared}{rgb}{0.6,0,0} % for strings
-\definecolor{javagreen}{rgb}{0.25,0.5,0.35} % comments
-\definecolor{javapurple}{rgb}{0.5,0,0.35} % keywords
-\definecolor{javadocblue}{rgb}{0.25,0.35,0.75} % javadoc
-
-\lstset{language=Java,
-	basicstyle=\ttfamily,
-	keywordstyle=\color{javapurple}\bfseries,
-	stringstyle=\color{javagreen},
-	commentstyle=\color{javagreen},
-	morecomment=[s][\color{javadocblue}]{/**}{*/},
-	numbers=left,
-	numberstyle=\tiny\color{black},
-	stepnumber=1,
-	numbersep=10pt,
-	tabsize=2,
-	showspaces=false,
-	showstringspaces=false}
-
-\lstdefinelanguage{scala}{
-  morekeywords={abstract,case,catch,class,def,%
-    do,else,extends,false,final,finally,%
-    for,if,implicit,import,match,mixin,%
-    new,null,object,override,package,%
-    private,protected,requires,return,sealed,%
-    super,this,throw,trait,true,try,%
-    type,val,var,while,with,yield},
-  otherkeywords={=>,<-,<\%,<:,>:,\#,@},
-  sensitive=true,
-  morecomment=[l]{//},
-  morecomment=[n]{/*}{*/},
-  morestring=[b]",
-  morestring=[b]',
-  morestring=[b]"""
-}
-
-\lstset{language=Scala,
-	basicstyle=\ttfamily,
-	keywordstyle=\color{javapurple}\bfseries,
-	stringstyle=\color{javagreen},
-	commentstyle=\color{javagreen},
-	morecomment=[s][\color{javadocblue}]{/**}{*/},
-	numbers=left,
-	numberstyle=\tiny\color{black},
-	stepnumber=1,
-	numbersep=10pt,
-	tabsize=2,
-	showspaces=false,
-	showstringspaces=false}
-
 % beamer stuff 
-\renewcommand{\slidecaption}{APP 09, King's College London, 2 December 2013}
+\renewcommand{\slidecaption}{APP 09, King's College London, 3 December 2013}
 \newcommand{\dn}{\stackrel{\mbox{\scriptsize def}}{=}}% for definitions
 \newcommand{\bl}[1]{\textcolor{blue}{#1}}
 
@@ -107,15 +55,11 @@
   \LARGE Privacy Policies (9)\\[-6mm] 
   \end{tabular}}\bigskip\bigskip\bigskip
 
-  %\begin{center}
-  %\includegraphics[scale=1.3]{pics/barrier.jpg}
-  %\end{center}
-
-\normalsize
+  \normalsize
   \begin{center}
   \begin{tabular}{ll}
   Email:  & christian.urban at kcl.ac.uk\\
-  Of$\!$fice: & S1.27 (1st floor Strand Building)\\
+  Office: & S1.27 (1st floor Strand Building)\\
   Slides: & KEATS (also homework is there)\\
   \end{tabular}
   \end{center}
@@ -126,31 +70,53 @@
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \mode<presentation>{
-\begin{frame}[c]
-\frametitle{Last Week}
+\begin{frame}[t]
+\frametitle{Checking Solutions}
+
+How can you check somebody's solution without revealing the solution?\pause\bigskip
 
-Recall, the Schroeder-Needham (1978) protocol is vulnerable to replay attacks.
+Alice and Bob solve crosswords. Alice knows the answer for 21D (folio) but doesn't 
+want to tell Bob.\medskip
+
+You use an English  dictionary:
 
-\begin{center}
-\begin{tabular}{@{}r@ {\hspace{1mm}}l@{}}
-\bl{$A \rightarrow S :$} & \bl{$A, B, N_A$}\\
-\bl{$S \rightarrow A :$} & \bl{$\{N_A, B, K_{AB},\{K_{AB}, A\}_{K_{BS}} \}_{K_{AS}}$}\\
-\bl{$A \rightarrow B :$} & \bl{$\{K_{AB}, A\}_{K_{BS}} $}\\
-\bl{$B \rightarrow A :$} & \bl{$\{N_B\}_{K_{AB}}$}\\
-\bl{$A \rightarrow B :$} & \bl{$\{N_B-1\}_{K_{AB}}$}\\
-\end{tabular}
-\end{center}\pause
+\begin{itemize}
+\item folio \onslide<4->{$\stackrel{1}{\rightarrow}$ individual }
+                \onslide<5->{$\stackrel{2}{\rightarrow}$ human}
+                \onslide<6->{$\stackrel{3}{\rightarrow}$ or \ldots}
+\only<3>{
+\begin{quote}
+``an \alert{individual} leaf of paper or parchment, either loose as one of a series or 
+forming part of a bound volume, which is numbered on the recto or front side only.''	
+\end{quote}}
+\only<4>{
+\begin{quote}
+``a single \alert{human} being as distinct from a group''
+\end{quote}}
+\only<5>{
+\begin{quote}
+``relating to \alert{or} characteristic of humankind''
+\end{quote}}
+\end{itemize}\bigskip\bigskip
 
-Fix: Replace messages 2 and 3 to include a timestamp:\bigskip
+\only<7->{
+hash functions...but Bob can only check once he has also the solution
+}
+
+\end{frame}}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
 
-\begin{minipage}{1.1\textwidth}
-\begin{center}
-\begin{tabular}{@{\hspace{-2mm}}r@ {\hspace{1mm}}l@{}}
-\bl{$S \rightarrow A :$} & \bl{$\{B, K_{\!AB}, T_S, \!\{K_{\!AB}, A, T_S\}_{K_{BS}} \}_{K_{AS}}$}\\
-\bl{$A \rightarrow B :$} & \bl{$\{K_{AB}, A, T_S\}_{K_{BS}} $}\\
-\end{tabular}
-\end{center}
-\end{minipage}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\mode<presentation>{
+\begin{frame}[c]
+\frametitle{Zero-Knowledge Proofs}
+
+Two remarkable properties:\bigskip
+
+\begin{itemize}
+\item Alice only reveals the fact that she knows a secret.\bigskip
+\item Having been convinced, Bob cannot use the evidence in order to convince Carol.
+\end{itemize}
 
 \end{frame}}
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
@@ -158,391 +124,97 @@
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \mode<presentation>{
 \begin{frame}[t]
-\frametitle{Denning-Sacco Fix}
+\frametitle{\begin{tabular}{@{}c@{}}The Idea\end{tabular}}
 
-Denning-Sacco (1981) suggested to add the timestamp, but omit the handshake:\bigskip
-
-\begin{minipage}{1.1\textwidth}
 \begin{center}
-\begin{tabular}{@{\hspace{-2mm}}r@ {\hspace{1mm}}l@{}}
-\bl{$A \rightarrow S :$} & \bl{$A, B$}\\
-\bl{$S \rightarrow A :$} & \bl{$\{B, K_{\!AB}, T_S, \!\{K_{\!AB}, A, T_S\}_{K_{BS}} \}_{K_{AS}}$}\\
-\bl{$A \rightarrow B :$} & \bl{$\{K_{AB}, A, T_S\}_{K_{BS}} $}\\
-\textcolor{lightgray}{$B \rightarrow A :$} & \textcolor{lightgray}{$\{N_B\}_{K_{AB}}$}\\
-\textcolor{lightgray}{$A \rightarrow B :$} & \textcolor{lightgray}{$\{N_B-1\}_{K_{AB}}$}\\
+\begin{tabular}{l@{\hspace{10mm}}r}
+\\[-10mm]
+\raisebox{10mm}{\large 1.} & \includegraphics[scale=0.1]{pics/alibaba1.png}\\
+\raisebox{10mm}{\large 2.} & \includegraphics[scale=0.1]{pics/alibaba2.png}\\
+\raisebox{10mm}{\large 3.} & \includegraphics[scale=0.1]{pics/alibaba3.png}
 \end{tabular}
 \end{center}
-\end{minipage}\bigskip
-
-they argue \bl{$A$} and \bl{$B$} can check that the messages are not replays of earlier 
-runs, by checking the time difference with when the protocol is last used
-\end{frame}}
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
-
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-\mode<presentation>{
-\begin{frame}[t]
-\frametitle{\begin{tabular}{@{}c@{}}Denning-Sacco-Lowe Fix of Fix\end{tabular}}
-
-Lowe (1997) disagreed and said the handshake should be kept, 
-otherwise:\bigskip 
 
-\begin{minipage}{1.1\textwidth}
-\begin{center}
-\begin{tabular}{@{\hspace{-7mm}}r@ {\hspace{1mm}}l@{}}
-\bl{$A \rightarrow S :$} & \bl{$A, B$}\\
-\bl{$S \rightarrow A :$} & \bl{$\{B, K_{\!AB}, T_S, \!\{K_{\!AB}, A, T_S\}_{K_{BS}} \}_{K_{AS}}$}\\
-\bl{$A \rightarrow B :$} & \bl{$\{K_{AB}, A, T_S\}_{K_{BS}} $}\\
-\bl{$I(A) \rightarrow B :$} & \bl{$\{K_{AB}, A, T_S\}_{K_{BS}} $}\hspace{5mm}\textcolor{black}{replay}\\
-\end{tabular}
-\end{center}
-\end{minipage}\bigskip
+\small
+\only<2>{
+\begin{textblock}{12}(2,13.3)
+Even if Bob has a hidden camera, a recording will not be convincing to anyone else 
+(Alice and Bob could have made it all up).
+\end{textblock}}
+\only<3>{
+\begin{textblock}{12}(2,13.3)
+Even worse, an observer present at the experiment would not be convinced.
+\end{textblock}}
 
-When is this a problem?\pause\medskip
-
-Assume \bl{$B$} is a bank and the message is ``Draw \pounds{1000} from \bl{$A$}'s
-account and transfer it to \bl{$I$}.''
 \end{frame}}
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \mode<presentation>{
-\begin{frame}[t]
-\frametitle{Privacy}
-
-\begin{minipage}{1.05\textwidth}
-\begin{itemize}
-\item we \alert{do} want that government data is made public (free maps for example)
-\item we \alert{do not} want that medical data becomes public (similarly tax data, school 
-records, job offers)\bigskip
-\item personal information can potentially lead to fraud 
-(identity theft)
-\end{itemize}\pause
-
-{\bf ``The reality'':}
-\only<2>{\begin{itemize}
-\item London Health Programmes lost in June unencrypted details of more than 8 million people
-(no names, but postcodes and details such as gender, age and ethnic origin)
-\end{itemize}}
-\only<3>{\begin{itemize}
-\item also in June Sony, got hacked: over 1M users' personal information, including passwords, email addresses, home addresses, dates of birth, and all Sony opt-in data associated with their accounts.
-\end{itemize}}
-\end{minipage}
-
-\end{frame}}
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
-
-   
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-\mode<presentation>{
 \begin{frame}[c]
-\frametitle{Privacy and Big Data}
-
-Selected sources of ``Big Data'':\smallskip{}
-
-\begin{itemize}
-\item Facebook 
-\begin{itemize}
-\item 40+ Billion photos (100 PB)
-\item 6 Billion messages daily (5 - 10 TB)
-\item 900 Million users  
-\end{itemize}
-\item Common Crawl
-\begin{itemize}
-\item covers 3.8 Billion webpages (2012 dataset)
-\item 50 TB of data
-\end{itemize}
-\item Google
-\begin{itemize}
-\item 20 PB daily (2008)
-\end{itemize}
-\item Twitter
-\begin{itemize}
-\item 7 Million users in the UK
-\item a company called Datasift is allowed to mine all tweets since 2010
-\item they charge 10k per month for other companies to target advertisement
-\end{itemize}
-\end{itemize}\pause
-
+\frametitle{Graph Isomorphism}
 
-\end{frame}}
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
-
-
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-\mode<presentation>{
-\begin{frame}[c]
-\frametitle{Cookies\ldots}
-
-``We have published a new cookie policy. It explains what cookies are 
-and how we use them on our site. To learn more about cookies and 
-their benefits, please view our cookie policy.\medskip
-
-If you'd like to disable cookies on this device, please view our information 
-pages on 'How to manage cookies'. Please be aware that parts of the 
-site will not function correctly if you disable cookies. \medskip
-
-By closing this 
-message, you consent to our use of cookies on this device in accordance 
-with our cookie policy unless you have disabled them.''
-
-
-\end{frame}}
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
-
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-\mode<presentation>{
-\begin{frame}[c]
-\frametitle{Scare Tactics}
+\begin{center}
+\begin{tabular}{l@{\hspace{10mm}}r}
+\includegraphics[scale=0.8]{pics/graphs.png}\\
+\end{tabular}
+\end{center}
 
-The actual policy reads:\bigskip
-
-``As we explain in our Cookie Policy, cookies help you to get the most 
-out of our websites.\medskip
-
-If you do disable our cookies you may find that certain sections of our 
-website do not work. For example, you may have difficulties logging in 
-or viewing articles.''
-
-
-
-
-\end{frame}}
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
-
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-\mode<presentation>{
-\begin{frame}[c]
-\frametitle{Netflix Prize}
-
-Anonymity is \alert{necessary} for privacy, but \alert{not} enough!\bigskip
-
-\begin{itemize}
-\item Netflix offered in 2006 (and every year until 2010) a 1 Mio \$ prize for improving their movie rating algorithm
-\item dataset contained 10\% of all Netflix users (appr.~500K)
-\item names were removed, but included numerical ratings as well as times of rating
-\item some information was \alert{perturbed} (i.e., slightly modified)
-\end{itemize}
-
-\hfill{\bf\alert{All OK?}}
-
+Finding an isomorphism between two graphs is an NP complete problem.
 \end{frame}}
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \mode<presentation>{
 \begin{frame}[c]
-\frametitle{Re-identification Attack}
-
-Two researchers analysed the data: 
+\frametitle{Graph Isomorphism Protocol}
 
-\begin{itemize}
-\item with 8 ratings (2 of them can be wrong) and corresponding dates that can have a margin 14-day error, 98\% of the
-records can be identified
-\item for 68\% only two ratings and dates are sufficient (for movie ratings outside the top 500)\bigskip\pause
-\item they took 50 samples from IMDb (where people can reveal their identity)
-\item 2 of them uniquely identified entries in the Netflix database (either by movie rating or by dates)
-\end{itemize}
-
-\end{frame}}
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
-
+Alice starts with knowing an isomorphism between graphs \bl{$G_1$} and \bl{$G_2$}\medskip
 
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-\mode<presentation>{
-\begin{frame}[c]
-\frametitle{}
-
-\begin{itemize}
-\item Birth data, postcode and gender (unique for\\ 87\% of the US population)
-\item Preferences in movies (99\% of 500K for 8 ratings)
-\end{itemize}\bigskip
+\begin{enumerate}
+\item Alice generates an isomorphic graph \bl{$H$} which she sends to Bob 
+\item Bob asks either for an isomorphism between \bl{$G_1$} and \bl{$H$}, or
+\bl{$G_2$} and \bl{$H$}	
+\item Alice and Bob repeat this procedure \bl{$n$} times	
+\end{enumerate}\pause
 
-Therefore best practices / or even law (HIPAA, EU): 
-
-\begin{itemize}
-\item only year dates (age group for 90 years or over), 
-\item no postcodes (sector data is OK, similarly in the US)\\
-\textcolor{gray}{no names, addresses, account numbers, licence plates}
-\item disclosure information needs to be retained for 5 years
-\end{itemize}
-
+these are called commitment algorithms
 \end{frame}}
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
-
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%    
+   
+   
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \mode<presentation>{
 \begin{frame}[c]
-\frametitle{How to Safely Disclose Information?}
-
-\only<1>{
-\begin{itemize}
-\item Assume you make a survey of 100 randomly chosen people.
-\item Say 99\% of the surveyed people in the 10 - 40 age group have seen the
-Gangnam video on youtube.\bigskip
-
-\item What can you infer about the rest of the population? 
-\end{itemize}}
-\only<2>{
-\begin{itemize}
-\item Is it possible to re-identify data later, if more data is released. \bigskip\bigskip\pause
-
-\item Not even releasing only  aggregate information prevents re-identification attacks.
-(GWAS was a public database of gene-frequency studies linked to diseases;
-you only needed partial DNA information  in order
-to identify whether an individual was part of the study --- DB closed in 2008) 
-\end{itemize}}
-
-\end{frame}}
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
-
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-\mode<presentation>{
-\begin{frame}[c]
-\frametitle{Differential Privacy}
-
-\begin{center}
-User\;\;\;\;    
-\begin{tabular}{c}
-tell me \bl{$f(x)$} $\Rightarrow$\\
-$\Leftarrow$ \bl{$f(x) + \text{noise}$}
-\end{tabular}
-\;\;\;\;\begin{tabular}{@{}c}
-Database\\
-\bl{$x_1, \ldots, x_n$}
-\end{tabular}
-\end{center}
+\frametitle{Non-Interactive ZKPs}
 
 
-\begin{itemize}
-\item \bl{$f(x)$} can be released, if \bl{$f$} is insensitive to
-individual entries  \bl{$x_1, \ldots, x_n$}\\
-\item Intuition: whatever is learned from the dataset would be learned regardless of whether
-\bl{$x_i$} participates\bigskip\pause 
-
-\item Noised needed in order to prevent queries:\\ Christian's salary $=$ 
-\begin{center}
-\bl{\large$\Sigma$} all staff $-$  \bl{\large$\Sigma$} all staff $\backslash$ Christian
-\end{center} 
-\end{itemize}
-
+\bigskip
+This is amazing: Alison can publish some data that contains no data about her secret,
+but can be used to convince anyone of the secret's existence.
 \end{frame}}
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \mode<presentation>{
 \begin{frame}[c]
-\frametitle{Adding Noise}
-
-Adding noise is not as trivial as one would wish:
-
-\begin{itemize}
-\item If I ask how many of three have seen the Gangnam video and get a result
-as follows 
-
-\begin{center}
-\begin{tabular}{l|c}
-Alice & yes\\
-Bob & no\\
-Charlie & yes\\
-\end{tabular}
-\end{center}
-
-then I have to add a noise of \bl{$1$}. So answers would be in the
-range of \bl{$1$} to \bl{$3$}
-
-\bigskip
-\item But if I ask five questions for all the dataset (has seen Gangnam video, is male, below 30, \ldots),
-then one individual can change the dataset by \bl{$5$}
-\end{itemize}
-
-\end{frame}}
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
-
-
+\frametitle{Problems of ZKPs}
 
 
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-\mode<presentation>{
-\begin{frame}[t]
-\frametitle{\begin{tabular}{@{}c@{}}Tor, Anonymous Webbrowsing\end{tabular}}
-
-\begin{itemize}
-\item initially developed by US Navy Labs, but then opened up to the world 
-\item network of proxy nodes
-\item a Tor client establishes a ``random'' path to the destination server (you cannot trace back where the information came from)\bigskip\pause
-\end{itemize}
-
-\only<2>{
-\begin{itemize}
-\item malicious exit node attack: someone set up 5 Tor exit nodes and monitored the traffic:
-\begin{itemize}
-\item a number of logons and passwords used by embassies (Usbekistan `s1e7u0l7c', while
-Tunesia `Tunesia' and India `1234')
-\end{itemize}
-\end{itemize}}
-\only<3>{
-\begin{itemize}
-\item bad apple attack: if you have one insecure application, your IP can be tracked through Tor
-\begin{itemize}
-\item background: 40\% of traffic on Tor is generated by BitTorrent
-\end{itemize}
-\end{itemize}}
-
-
-\end{frame}}
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
-
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-\mode<presentation>{
-\begin{frame}[t]
-\frametitle{\begin{tabular}{@{}c@{}}Skype Secure Communication\end{tabular}}
-
-\begin{itemize}
-\item Skype used to be known as a secure online communication (encryption cannot be disabled), 
-but \ldots\medskip
-
-\item it is impossible to verify whether crypto algorithms are correctly used, or whether  there are backdoors.\bigskip
- 
-\item recently someone found out that you can reset the password of somebody else's
-account, only knowing their email address (needed to suspended the password reset feature temporarily)
-\end{itemize}
-
-
-\end{frame}}
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
-
-
-
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-\mode<presentation>{
-\begin{frame}[c]
-\frametitle{\begin{tabular}{@{}c@{}}Take Home Point\end{tabular}}
-
-According to Ross Anderson: \bigskip
-\begin{itemize}
-\item Privacy in a big hospital is just about doable.\medskip
-\item How do you enforce privacy  in something as big as Google
-or complex as Facebook? No body knows.\bigskip
-
-Similarly, big databases imposed by government
-\end{itemize}
-
-
+\bigskip
+This is amazing: Alison can publish some data that contains no data about her secret,
+but can be used to convince anyone of the secret's existence.
 \end{frame}}
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \mode<presentation>{
 \begin{frame}[c]
-\frametitle{\begin{tabular}{@{}c@{}}Next Week\end{tabular}}
-
-Homework: Which areas should I focus on?
+\frametitle{Random Number Generators}
 
 
 \end{frame}}
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
-
 \end{document}
 
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