sen-material: comparison handouts/ho08.tex

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 \documentclass{article}
 \usepackage{../style}
 \usepackage{../graphics}
 \usepackage{../langs}
+\usepackage{../data}
 \begin{document}
-\fnote{\copyright{} Christian Urban, 2014}
+\fnote{\copyright{} Christian Urban, 2014, 2015}
 \section*{Handout 8 (Bitcoins)}
 In my opinion Bitcoins are an elaborate Ponzi
 scheme\footnote{\url{http://en.wikipedia.org/wiki/Ponzi_scheme}}---still
 leading zeros a hash-value has, but rather whether it is below
 a \emph{target}. The hardness of the puzzle can actually be
 controlled by changing the target according to the available
 computational power available. I think the adjustment of the
 hardness of the problems is done every 2060 blocks
-(appr.~every two weeks). I am not sure whether this is an
+(appr.~every two weeks). The aim of the adjustment is that on
-automatic process. The aim of the adjustment is that on
 average the Bitcoin network will most likely solve a puzzle
 within 10 Minutes.
 \begin{center}
 \includegraphics[scale=0.37]{../pics/blockchainsolving.png}
 amassing such an amount of computing power is practically
 impossible for a single person or even a moderately large
 group.
 Connected with the 6-confirmation rule is an interesting
-phenomenon. On average, it would take several years for a typical
+phenomenon. On average, it would take several years for a
-computer to solve a proof-of-work puzzle, so an individual’s chance of
+typical computer to solve a proof-of-work puzzle, so an
-ever solving one before the rest of the world, which typically takes
+individual’s chance of ever solving one before the rest of the
-only 10 minutes, is negligibly low. Therefore many people join groups
+world, which typically takes only 10 minutes, is negligibly
-called \emph{mining pools} that collectively work to solve blocks, and
+low. Therefore many people join groups called \emph{mining
-distribute rewards based on work contributed. These mining pools act
+pools} that collectively work to solve blocks, and distribute
-somewhat like lottery pools among co-workers, except that some of
+rewards based on work contributed. These mining pools act
-these pools are quite large, and comprise more than 20\% of all the
+somewhat like lottery pools among co-workers, except that some
-computers in the network. It is said that BTC, a large mining pool,
+of these pools are quite large, and comprise more than 20\% of
-has limited its number of members in order to not solve more than 6
+all the computers in the network. It is said that BTCC, a
-blocks in a row. Otherwise this would undermine the trust in Bitcoins,
+large mining pool, has limited its number of members in order
-which is also not in the interest of BTC, I guess.  Some statistics on
+to not solve more than 6 blocks in a row. Otherwise this would
-mining pools can be seen at
+undermine the trust in Bitcoins, which is also not in the
+interest of BTCC, I guess. Some statistics on mining pools can
+be seen at
 \begin{center}
 \url{https://blockchain.info/pools}
 \end{center}
 \subsubsection*{Bitcoins for Real}
-Let us now turn to the nitty gritty details. As a participant in the
+Let us now turn to the nitty gritty details. As a participant
-Bitcoin networ you need to generate and store a public-private key
+in the Bitcoin network you need to generate and store a
-pair. The public key you need to advertise in order to receive
+public-private key pair. The public key you need to advertise
-payments (transactions). The private key needs to be securely stored.
+in order to receive payments (transactions). The private key
-For this there seem to be three possibilities
+needs to be securely stored. For this there seem to be three
+possibilities
 \begin{itemize}
 \item an electronic wallet on your computer
 \item a cloud-based storage (offered by some Bitcoin services)
 \item paper-based
 \end{itemize}
-\noindent The first two options of course offer convenience for making
+\noindent The first two options of course offer convenience
-and receiving transactions. But given the nature of the private keys
+for making and receiving transactions. But given the nature of
-and how much security relies on them (recall if somebody gets hold of
+the private keys and how much security relies on them (recall
-it, your Bitcoins are quickly lost forever) I would opt for the third
+if somebody gets hold of it, your Bitcoins are quickly lost
-option for anything except for trivial amounts of Bitcoins. As we have
+forever) I would opt for the third option for anything except
-seen earlier in the course, securing a computer system that it can
+for trivial amounts of Bitcoins. As we have seen earlier in
-withstand a breakin is still very much an unsolved problem.
+the course, securing a computer system that it can withstand a
+targeted breakin is still very much an unsolved problem.
 An interesting fact with Bitcoin keys is that there is no
 check for duplicate addresses. This means when generating a
 public-private key, you should really start with a carefully
 chosen random number such that there is really no chance to
 unexpected ways. You probably have heard about, or even used,
 Amazon's Elastic Compute Cloud (EC2). Essentially, Amazon is
 selling computing power that you can use to run your web site,
 for example. It is \emph{elastic} in the sense that if you
 have a lot of visitors, you pay a lot, if you have only a few,
-then it is cheap. In order to bill you they, you need to set
+then it is cheap. In order to bill you, you need to set
 up an account with Amazon and receive some secret keys in
 order to authenticate you. The clever (but also dangerous) bit
 is that you upload the code of your web site to GitHub and
 Amazon will pull it from there. You can probably already guess
 where this is going: in order to learn about Amazon's API, it

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