--- a/slides/slides08.tex Tue Nov 18 03:27:16 2014 +0000
+++ b/slides/slides08.tex Tue Nov 18 12:24:17 2014 +0000
@@ -74,8 +74,8 @@
\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
+\item anonymous?\pause
+\item surely a ponzi scheme!
\end{itemize}
\begin{textblock}{7}(11.5,10)
@@ -91,15 +91,18 @@
\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}
@@ -109,7 +112,7 @@
\begin{frame}
\frametitle{Underlying Ideas}
-Establishing trust in a completely
+It establishing trust in a completely
untrusted environment\medskip
\begin{itemize}
@@ -120,7 +123,7 @@
\begin{center}
If Alice sends you: \bl{$msg, \{msg\}_{K^{priv}_{Alice}}$}
-\ldots
+\ldots ?
\end{center}
\end{frame}
@@ -136,9 +139,10 @@
\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}
@@ -157,13 +161,14 @@
\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}
@@ -178,11 +183,11 @@
\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
+\item Alice hasn’t already spent this infocoin.\bigskip
+\item If yes, then Bob tells the bank he accepts 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}
@@ -217,6 +222,12 @@
\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}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@@ -286,7 +297,7 @@
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[t]
-\frametitle{Proof-Of-Work}
+\frametitle{!! Proof-of-Work !!}
The idea is counterintuitive and involves a combination of two
ideas:\bigskip
@@ -305,7 +316,7 @@
\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}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@@ -315,7 +326,7 @@
\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]
@@ -361,8 +372,8 @@
\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.
+If we don’t have such an ordering at any given moment
+then it may not be clear who owns which infocoins.
\begin{center}
\includegraphics[scale=0.38]{../pics/bitcoin_unconfirmed.png}
@@ -407,7 +418,7 @@
\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.
@@ -419,7 +430,7 @@
\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}
@@ -431,7 +442,7 @@
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}
-\frametitle{Racing Agianst the World}
+\frametitle{Racing Against the World}
\begin{columns}
\begin{column}{4.5cm}
@@ -462,7 +473,7 @@
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
@@ -541,6 +552,25 @@
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\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}
@@ -589,6 +619,7 @@
\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.
@@ -601,30 +632,35 @@
\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
-concerns, however.
+transactions are public.
-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.
+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}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%