sen-material: comparison slides/slides08.tex

equal deleted inserted replaced

-:7bd723cb9b32
+:edbd731e8bee
 \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 anonymous?\pause
-\item a ponzi scheme
+\item surely a ponzi scheme!
 \end{itemize}
 \begin{textblock}{7}(11.5,10)
 \includegraphics[scale=0.21]{../pics/bitcoin_ledgers.png}
 \end{textblock}
 \begin{frame}[t]
 \frametitle{Bitcoins}
 \begin{itemize}
 \item you create a public-private key pair
-\item you have a wallet which can be
+\item you have a `wallet' which can be
 \begin{itemize}
-\item electronic (on you computer, passwords)
+\item electronic (on your computer, passwords)
 \item cloud-based (passwords)
 \item paper-based
 \end{itemize}
+and contains only the public-private key
+\item Bitcoins can be stolen and lost
 \item Mt.~Gox: hacked $\Rightarrow$ insolvent
-\item no form of dispute resolution
+\item no form of dispute resolution (against current
+consumer laws)
 \end{itemize}
 \end{frame}
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \begin{frame}
 \frametitle{Underlying Ideas}
-Establishing trust in a completely
+It 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
+\ldots ?
 \end{center}
 \end{frame}
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \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 Alice cannot deny the ``intend'' of sending Bob money\pause\bigskip
 \item forgery possible only after Alice created the string
-\item Q: What is money? --- A: Well string above
+\item Q: What is money?\\
+A: Well a string like above
 (or later messages like that)
 \end{itemize}
 \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
+again (did she mean to send 10 ICs?)\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)
+\item but then we need a trusted source of serial numbers
+(e.g.~a bank)
 \end{itemize}
 \end{frame}
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 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 Alice hasn’t already spent this infocoin.\bigskip
-\item If yes, then Bob tells the bank he accept the infocoin
+\item If yes, then Bob tells the bank he accepts the infocoin.
-\item the bank updates the records to show that 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
+no longer belongs to Alice.
 \end{itemize}
 \end{frame}
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \frametitle{Blockchain}
 \begin{center}
 \includegraphics[scale=0.5]{../pics/bitcoinblockchain0.png}
 \end{center}
+\begin{itemize}
+\item each block is hashed and contains a reference to
+the earlier block; ``validates'' potentially more than one
+transaction
+\end{itemize}
 \end{frame}
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \end{frame}
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \begin{frame}[t]
-\frametitle{Proof-Of-Work}
+\frametitle{!! Proof-of-Work !!}
 The idea is counterintuitive and involves a combination of two
 ideas:\bigskip
 \begin{bubble}[10cm]
 \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
+roughly every 4 years (currently 25 BC); 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
+\alert{salt} so the hash starts with a long run of
 zeros?\bigskip
 \begin{bubble}[10cm]
 \begin{tabular}{l}
 \footnotesize\code{h("Hello, world!0") =}\\
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \begin{frame}[t]
 \frametitle{Order of Transactions}
-If we don’t have such an ordering then at any given moment it
+If we don’t have such an ordering at any given moment
-may not be clear who owns which infocoins.
+then it may not be clear who owns which infocoins.
 \begin{center}
 \includegraphics[scale=0.38]{../pics/bitcoin_unconfirmed.png}
 \end{center}
 \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
+The rule is: 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
+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}
+\frametitle{Racing Against the World}
 \begin{columns}
 \begin{column}{4.5cm}
 \includegraphics[scale=0.3]{../pics/bitcoin_doublespend_blockchain_race.png}
 \end{column}
 \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.
+minutes, is negligibly 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
 \end{frame}
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{A Block in the Blockchain}
+\begin{center}
+\includegraphics[scale=0.38]{../pics/bitcoin_unconfirmed.png}
+\end{center}
+\begin{itemize}
+\item each block is hashed and contains a reference to
+the earlier block
+\item contains the ``salt'' and address of whoever solved the
+puzzle
+\end{itemize}
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \begin{frame}
 \frametitle{Transaction History}
 you can follow back the transaction history until
 you reach either
 \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
+\item you cannot meddle with the ``history''
 \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}
+\includegraphics[scale=0.4]{../pics/bitcointornetwork.png}
 \end{center}
+ledger is public forever; everybody can inspect
+how money was transferred from which address to
+which address
 \end{frame}
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \begin{frame}[t]
 \frametitle{Anonymity}
+\small
 Bitcoins may not be ideal for money laundering because all
-transactions are public.[218] Authorities have expressed
+transactions are public.
-concerns, however.
+How anonymous is Bitcoin? Many people claim that Bitcoin can
-How anonymous is Bitcoin? Many people claim that Bitcoin can be used
+be used anonymously. This claim has led to the formation of
-anonymously. This claim has led to the formation of marketplaces such
+marketplaces such as Silk Road (and various successors), which
-as Silk Road (and various successors), which specialize in illegal
+specialize in illegal goods. However, the claim that Bitcoin
-goods. However, the claim that Bitcoin is anonymous is a myth. The
+is anonymous is a myth. The block chain is public, meaning
-block chain is public, meaning that it’s possible for anyone to see
+that it’s possible for anyone to see every Bitcoin transaction
-every Bitcoin transaction ever. Although Bitcoin addresses aren’t
+ever. Although Bitcoin addresses aren’t immediately associated
-immediately associated to real-world identities, computer scientists
+to real-world identities, computer scientists have done a
-have done a great deal of work figuring out how to de-anonymize
+great deal of work figuring out how to de-anonymize
-“anonymous” social networks. The block chain is a marvellous target
+“anonymous” social networks. The block chain is a marvellous
-for these techniques.
+target for these techniques.
 \end{frame}
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \begin{frame}[t]

changeset 316	edbd731e8bee
parent 315	7bd723cb9b32
child 317	0cdfa8ef4aa2