# HG changeset patch
# User Christian Urban <christian dot urban at kcl dot ac dot uk>
# Date 1416281236 0
# Node ID 7bd723cb9b325442a9115fff4eccf75c769fb830
# Parent  e01f55e7485a1f70b15ef67dce517ff4f94ac1d3
updated

diff -r e01f55e7485a -r 7bd723cb9b32 handouts/ho07.tex
--- a/handouts/ho07.tex	Mon Nov 17 18:49:13 2014 +0000
+++ b/handouts/ho07.tex	Tue Nov 18 03:27:16 2014 +0000
@@ -387,6 +387,11 @@
 http://repository.cmu.edu/cgi/viewcontent.cgi?article=1077&context=hcii
 https://josephhall.org/papers/NYU-MCC-1303-S2012_privacy_syllabus.pdf
 http://www.jetlaw.org/wp-content/uploads/2014/06/Bambauer_Final.pdf
+http://www.cs.cmu.edu/~yuxiangw/docs/Differential%20Privacy.pdf
+https://www.youtube.com/watch?v=Gx13lgEudtU
+https://www.cs.purdue.edu/homes/ctask/pdfs/CERIAS_Presentation.pdf
+http://www.futureofprivacy.org/wp-content/uploads/Differential-Privacy-as-a-Response-to-the-Reidentification-Threat-Klinefelter-and-Chin.pdf
+http://www.cis.upenn.edu/~aaroth/courses/slides/Overview.pdf
 
 %%% Local Variables: 
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diff -r e01f55e7485a -r 7bd723cb9b32 slides/slides08.pdf
Binary file slides/slides08.pdf has changed
diff -r e01f55e7485a -r 7bd723cb9b32 slides/slides08.tex
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/slides/slides08.tex	Tue Nov 18 03:27:16 2014 +0000
@@ -0,0 +1,665 @@
+\documentclass[dvipsnames,14pt,t]{beamer}
+\usepackage{../slides}
+\usepackage{../graphics}
+\usepackage{../langs}
+
+\usetikzlibrary{shapes}
+
+% beamer stuff 
+\renewcommand{\slidecaption}{APP 08, King's College London}
+\newcommand{\bl}[1]{\textcolor{blue}{#1}}
+
+\newcommand{\DOWNarrow}[3]{%
+\begin{textblock}{0}(#2,#3)%
+\onslide<#1>{%
+\begin{tikzpicture}%
+\node at (0,0) [single arrow, shape border rotate=270, fill=red,text=red]{a};%
+\end{tikzpicture}}%
+\end{textblock}}
+\newcommand{\LEFTarrow}[3]{%
+\begin{textblock}{0}(#2,#3)%
+\onslide<#1>{%
+\begin{tikzpicture}%
+\node at (0,0) [single arrow, shape border rotate=180, fill=red,text=red]{a};%
+\end{tikzpicture}}%
+\end{textblock}}
+
+
+\begin{document}
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{%
+  \begin{tabular}{@ {}c@ {}}
+  \\
+  \LARGE Access Control and \\[-3mm] 
+  \LARGE Privacy Policies (8)\\[-6mm] 
+  \end{tabular}}\bigskip\bigskip\bigskip
+
+  \normalsize
+  \begin{center}
+  \begin{tabular}{ll}Ch
+  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}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%     
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+% student prticipation
+\begin{frame}
+\frametitle{Bitcoins}
+
+\begin{center}
+\Huge\bf ?
+\end{center}
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{Bitcoins from 10,000m}
+
+\begin{itemize}
+\item a crypto ``currency'' by Satoshi Nakamoto (likely a pen name)
+\item a digital resource designed to be scarce 
+  (max 21 Mio bitcoins---deflationary currency) 
+\item mined by solving special puzzles involving hashes
+\item transaction history (ledger/blockchain) is P2P distributed (12 GB)
+\item two ``mining pools'' produce\\ currently more than 50\% 
+  of bitcoins 
+\item can be stolen and also lost
+\item anoynmous?\pause
+\item a ponzi scheme
+\end{itemize}
+
+\begin{textblock}{7}(11.5,10)
+\includegraphics[scale=0.21]{../pics/bitcoin_ledgers.png}
+\end{textblock}
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{Bitcoins}
+
+\begin{itemize}
+\item you create a public-private key pair
+\item you have a wallet which can be
+\begin{itemize}
+\item electronic (on you computer, passwords)
+\item cloud-based (passwords)
+\item paper-based
+\end{itemize}
+
+\item Mt.~Gox: hacked $\Rightarrow$ insolvent
+\item no form of dispute resolution
+\end{itemize}
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}
+\frametitle{Underlying Ideas}
+
+Establishing trust in a completely 
+untrusted environment\medskip
+
+\begin{itemize}
+\item public-private key encryption\medskip
+\item digital signatures\medskip
+\item cryptographic hashing (SHA-256)
+\end{itemize}
+
+\begin{center}
+If Alice sends you: \bl{$msg, \{msg\}_{K^{priv}_{Alice}}$}
+\ldots
+\end{center}
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{Lets Start with Infocoins}
+
+\begin{center}
+\bl{$\{\text{I, Alice, am giving Bob one infocoin.}\}_{K^{priv}_{Alice}}$}
+\end{center}\bigskip
+
+\begin{itemize}
+\item no-one else could have created that message
+\item Alice cannot deny the ``intend''\pause\bigskip
+\item forgery possible only after Alice created the string
+\item Q: What is money? --- A: Well string above
+  (or later messages like that)
+\end{itemize}
+
+
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{Double Spend}
+
+\begin{center}
+\bl{$\{\text{I, Alice, am giving Bob one infocoin.}\}_{K^{priv}_{Alice}}$}
+\end{center}
+
+\begin{itemize}
+\item Alice could keep sending Bob this message over and over
+      again\pause
+\item we need to have a serial number
+\begin{center}
+\bl{$\{\text{I, Alice, am giving Bob infocoin \#1234567.}\}_{K^{priv}_{Alice}}$}
+\end{center}\pause\medskip
+
+\item but then we need a trusted source of serial numbers (e.g.~bank)
+\end{itemize}
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{No Banks Please}
+
+With banks we could implement:
+
+\begin{itemize}
+\item Bob asks the bank whether the infocoin with that serial
+      number belongs to Alice and
+\item Alice hasn’t already spent this infocoin. 
+\item If yes, then Bob tells the bank he accept the infocoin
+\item the bank updates the records to show that the infocoin
+      with that serial number is now in Bob’s possession and
+      no longer belongs to Alice\bigskip\pause
+\end{itemize}
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{Blockchain}
+
+The solution for double spend: 
+
+\begin{itemize}
+\item make everybody the bank, everybody has the entire
+      transaction history --- will be called
+      \alert{blockchain}\medskip
+\item Bob checks whether infocoin belongs to Alice and then
+      broadcasts the message to anybody else 
+\end{itemize}
+
+\begin{center}
+\includegraphics[scale=0.21]{../pics/bitcoin_ledgers.png}
+\end{center}
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{Blockchain}
+
+\begin{center}
+\includegraphics[scale=0.5]{../pics/bitcoinblockchain0.png}
+\end{center}
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{Transaction Graph}
+
+\mbox{}\hspace{3cm}older \hspace{3cm} current
+
+\begin{center}
+\includegraphics[scale=0.5]{../pics/blockchain.png}
+\end{center}
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{Double Spend Again}
+
+\begin{bubble}[10cm]\addtolength{\leftmargini}{5mm}
+\begin{itemize}
+\item I , Alice, am giving Bob one infocoin, with serial
+      number 1234567.
+\item I, Alice, am giving \alt<2->{\alert{Alice}}{Charlie} 
+      one infocoin.
+\end{itemize}
+\end{bubble}\bigskip
+
+How should other people update their blockchain (public
+register)?\pause
+
+
+\begin{center}
+\includegraphics[scale=0.3]{../pics/bitcoindisagreement.png}
+\end{center}
+
+
+Once enough people have broadcast that message, everyone
+updates their block chain to show that infocoin 1234567 now
+belongs to Bob, and the transaction is complete.
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{Creating Agreement}
+
+\begin{bubble}[10cm]
+Once \alert{enough} people have broadcast that message, 
+everyone updates their block chain to show that infocoin 
+1234567 now belongs to Bob, and the transaction is accepted.
+\end{bubble}\bigskip\bigskip
+\pause
+
+\small
+But what if Alice sets up a large number of separate
+identities, let’s say a billion, on the Infocoin network. When
+Bob asks the network to validate the transaction, Alice’s
+puppet identities say ``Yes his transaction is validated'',
+while actually the rest network says Alice's transaction 
+is OK?
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{Proof-Of-Work}
+
+The idea is counterintuitive and involves a combination of two
+ideas:\bigskip
+
+\begin{bubble}[10cm]
+\addtolength{\leftmargini}{5mm}
+\begin{itemize}
+
+\item to (artificially) make it computationally costly for
+      network users to validate transactions, and
+
+\item to reward them for trying to help validate transactions
+\end{itemize}
+\end{bubble}\pause\bigskip
+
+\small
+this is called mining: whoever validates a transaction will be awarded with
+50 bitcoins --- this halves every 210,000 transactions or
+roughly every 4 years; no new bitcoins after 2140 -- then only 
+transaction fees
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{Solving Puzzles}
+
+Given a string, say \code{"Hello, world!"}, what is the 
+\alert{salt} that the hash starts with a long run of 
+zeros?\bigskip
+
+\begin{bubble}[10cm]
+\begin{tabular}{l}
+\footnotesize\code{h("Hello, world!0") =}\\
+\;\;\scriptsize\code{1312af178c253f84028d480a6adc1e25e81caa44c749ec81976192e2ec934c64}\\
+\pause
+\footnotesize\code{h("Hello, world!1") =}\\ 
+\;\;\scriptsize\code{e9afc424b79e4f6ab42d99c81156d3a17228d6e1eef4139be78e948a9332a7d8}\\
+\pause
+\ldots\\
+\footnotesize\code{h("Hello, world!4250") =}\\ 
+\;\;\scriptsize\code{0000c3af42fc31103f1fdc0151fa747ff87349a4714df7cc52ea464e12dcd4e9}
+\end{tabular}
+\end{bubble}
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{Hardness}
+
+If we want the output hash value to begin with 10 zeroes,
+say, then we will need, on average, to try $16^{10} \approx
+10^{12}$ different salts before we find a suitable nonce. 
+
+Hardness can be controlled by setting a \alert{target} (maximum
+number).
+
+\begin{center}
+\includegraphics[scale=0.37]{../pics/blockchainsolving.png}
+\end{center}
+
+\begin{textblock}{7}(7,10)
+10 mins
+\end{textblock}
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{Order of Transactions}
+
+If we don’t have such an ordering then at any given moment it
+may not be clear who owns which infocoins.
+
+\begin{center}
+\includegraphics[scale=0.38]{../pics/bitcoin_unconfirmed.png}
+\end{center}
+
+\small
+Say, miner David is lucky and finds a suitable salt
+to confirm the transactions. Celebration!\pause \hspace{5mm}??
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{Forks}
+
+Typically the blockchain will look as follows
+
+\begin{center}
+\includegraphics[scale=0.65]{../pics/block_chain1.png}
+\end{center}
+
+\pause
+But every so often there is a fork
+
+\begin{center}
+\includegraphics[scale=0.65]{../pics/block_chain_fork.png}
+\end{center}
+
+\small
+\ldots{}bugger this is exactly what we are trying to avoid
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+
+The tie is broken if another block is solved
+
+\begin{center}
+\includegraphics[scale=0.4]{../pics/bitcoin_blockchain_branches.png}
+\end{center}
+
+\small
+The rule is this: if a fork occurs, people on the network keep
+track of all forks. But at any given time, miners only work
+to extend whichever fork is longest in their copy of the block
+chain.
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{Double Spending Again}
+
+So if Alice wants to fake it she needs to produce
+a longer chain:
+
+\begin{center}
+\includegraphics[scale=0.4]{../pics/bitcoin_blockchain_double_spend.png}
+\end{center}
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}
+\frametitle{Racing Agianst the World}
+
+\begin{columns}
+\begin{column}{4.5cm}
+\includegraphics[scale=0.3]{../pics/bitcoin_doublespend_blockchain_race.png}
+\end{column}
+\begin{column}{5.5cm}
+\includegraphics[scale=0.3]{../pics/bitcoin_transaction_order_race.png}
+\end{column}
+\end{columns}\bigskip\bigskip\pause
+
+\small
+A transaction is ``confirmed'' if:\smallskip
+
+(1) it is part of a block in the longest fork, and (2) at
+least 5 blocks follow it in the longest fork. In this case we
+say that the transaction has ``6 confirmations''.\bigskip
+
+\footnotesize (might take 1h+\ldots but for creditcards you have 
+6 months chargeback)
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{Mining Pools}
+
+\begin{bubble}[10cm]
+On average, it would take several years for a typical computer
+to solve a block, so an individual’s chance of ever solving
+one before the rest of the network, which typically takes 10
+minutes, is very low.
+\end{bubble}\bigskip\pause
+
+\small
+Many people join groups called mining pools that collectively
+work to solve blocks, and distribute rewards based on work
+contributed. These act somewhat like lottery pools among
+co-workers, except that some of these pools are quite large,
+and comprise more than 20\% of all the computers in the
+network.\medskip
+
+\footnotesize
+BTC, the largest mining pool, has limited its members to 
+not solve more than 6 blocks in a row.
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{Bitcoins for Real}
+
+\begin{itemize}
+\item you need a public-private key (the hash of the 
+public key to determines your bitcoin address) 
+
+\item if you want to receive bitcoins, you publicise 
+this address
+
+\item there are $2^{160}$ possibilities\\ 
+(no check for duplicates)
+\end{itemize}
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[c]
+\frametitle{A Transaction Msg}
+\small
+\lstinputlisting[language=Scala,
+                 numbersep=3pt, 
+                 xleftmargin=-6mm]{msg}
+
+\DOWNarrow{2}{3.5}{1.6}
+\LEFTarrow{3}{3.5}{3}
+\LEFTarrow{4}{4.7}{4}
+\LEFTarrow{4}{5.4}{4.8}
+\LEFTarrow{5}{5.4}{5.6}
+\LEFTarrow{6}{5}{6.4}
+\DOWNarrow{7}{6}{8.2}
+\LEFTarrow{8}{5}{9.7}
+\DOWNarrow{9}{7}{9.7}
+\DOWNarrow{9}{10}{9.7}
+\LEFTarrow{10}{9}{12}
+\DOWNarrow{11}{12.5}{12}
+
+
+\begin{textblock}{0}(7,3)%
+\small
+\onslide<2,4,7,8,9,10,11,12>{
+\begin{bubble}[6cm]%
+\only<2>{the hash of the msg that follows; kind of serial number}
+\only<4>{the transaction has one inout and one output (could be more)}
+\only<7>{the hash of the incoming transaction (incoming serial number)}
+\only<8>{use the 0th output of the incoming transaction}
+\only<9>{the public key and signature of the sender}
+\only<10>{use $x$ amount of the incoming money}
+\only<11>{public key of the receiver}
+\only<12>{you do not need a central authority to issue serial numbers\bigskip\\
+there are no ``coins'', just a long series of transactions}
+\end{bubble}}
+\end{textblock}
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}
+\frametitle{Transaction History}
+
+you can follow back the transaction history until
+you reach either
+
+\begin{itemize}
+\item the genesis block (a transaction without input of
+50 bitcoins)
+\item coinbase transaction (this is the reward of the
+miner who validated a block of transactions in the blockchain)
+
+\end{itemize}
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{Lost Bitcoins?}
+
+\begin{itemize}
+\item somebody needs to be able to generate a key-pair
+  for the signature (for this you need the private 
+  key)\bigskip
+
+\item somebody spends your bitcoins fraudulently
+  (you cannot charge them back)\ldots{} bad luck
+
+\item you can send bitcoins to a ``non-existing'' address
+  (Mt.~Gox)
+\end{itemize}
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{Good Points}
+
+An attacker can't:
+
+\begin{itemize}
+\item reverse other people's transactions
+\item change the number of coins generated per block
+\item create coins out of thin air
+\item send coins that never belonged to an attacker
+\end{itemize}\bigskip
+
+The system can be scaled to all world transactions. 
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{But I did not Inhale}
+
+\begin{center}
+\includegraphics[scale=0.04]{../pics/bitcointornetwork.png}
+\end{center}
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{Anonymity}
+
+Bitcoins may not be ideal for money laundering because all
+transactions are public.[218] Authorities have expressed
+concerns, however. 
+
+How anonymous is Bitcoin? Many people claim that Bitcoin can be used
+anonymously. This claim has led to the formation of marketplaces such
+as Silk Road (and various successors), which specialize in illegal
+goods. However, the claim that Bitcoin is anonymous is a myth. The
+block chain is public, meaning that it’s possible for anyone to see
+every Bitcoin transaction ever. Although Bitcoin addresses aren’t
+immediately associated to real-world identities, computer scientists
+have done a great deal of work figuring out how to de-anonymize
+“anonymous” social networks. The block chain is a marvellous target
+for these techniques.
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{Bitcoin vs Gov}
+
+Purported absence of potential government interference?
+\pause 
+Far from it:
+  
+\begin{itemize}
+  \item government could compel ``mayor players'' to blacklist
+     bitcoins (exchanges)
+  \item coerce developer community (e.g.~Lavabit)
+  \item put pressure on mining pools, or be big a miner 
+  itself
+\end{itemize} 
+
+\begin{center}
+\includegraphics[scale=0.04]{../pics/nsautah1.jpg}
+\hspace{3mm}
+\includegraphics[scale=0.031]{../pics/nsautah2.jpg}
+\end{center}
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
+
+
+
+
+\end{document}
+
+%%% Local Variables:  
+%%% mode: latex
+%%% TeX-master: t
+%%% End: 
+