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A Short Introduction to the World of Cryptocurrencies
Aleksander Berentsen and Fabian Schär
1 INTRODUCTION
Bitcoin originated with the white paper that was published in 2008 under the pseudonym
“Satoshi Nakamoto.” It was published via a mailing list for cryptography and has a similar
appearance to an academic paper. e creators’ original motivation behind Bitcoin was to
develop a cash-like payment system that permitted electronic transactions but that also
included many of the advantageous characteristics of physical cash. To understand the spe-
cic features of physical monetary units and the desire to develop digital cash, we will begin
our analysis by considering a simple cash transaction.
1.1 Cash
Cash is represented by a physical object, usually a coin or a note. When this object is
handed to another individual, its unit of value is also transferred, without the need for a third
party to be involved (Figure 1). No credit relationship arises between the buyer and the seller.
is is why it is possible for the parties involved to remain anonymous.
e great advantage of physical cash is that whoever is in possession of the physical object
is by default the owner of the unit of value. is ensures that the property rights to the units
In this article, we give a short introduction to cryptocurrencies and blockchain technology. e focus
of the introduction is on Bitcoin, but many elements are shared by other blockchain implementations
and alternative cryptoassets. e article covers the original idea and motivation, the mode of operation
and possible applications of cryptocurrencies, and blockchain technology. We conclude that Bitcoin
has a wide range of interesting applications and that cryptoassets are well suited to become an
important asset class. (JEL G23, E50, E59)
Federal Reserve Bank of St. Louis Review, First Quarter 2018, 100(1), pp. 1-16.
https://doi.org/10.20955/r.2018.1-16
Aleksander Berentsen is a research fellow at the Federal Reserve Bank of St. Louis and a professor of economic theory at the University of Basel.
Fabian Schär is managing director of the Center for Innovative Finance at the Faculty of Business and Economics, University of Basel.
© 2018, Federal Reserve Bank of St. Louis. The views expressed in this article are those of the author(s) and do not necessarily reect the views of
the Federal Reserve System, the Board of Governors, or the regional Federal Reserve Banks. Articles may be reprinted, reproduced, published,
distributed, displayed, and transmitted in their entirety if copyright notice, author name(s), and full citation are included. Abstracts, synopses,
and other derivative works may be made only with prior written permission of the Federal Reserve Bank of St. Louis.
Federal Reserve Bank of St. Louis REVIEW First Quarter 2018 1
Berentsen and Schär
2 First Quarter 2018 Federal Reserve Bank of St. Louis REVIEW
of value circulating in the economy are always clearly established, without a central authority
needing to keep accounts. Furthermore, any agent can participate in a cash payment system;
nobody can be excluded. ere is a permissionless access to it. Cash, however, also has disad-
vantages. Buyers and sellers have to be physically present at the same location in order to
trade, which in many situations makes its use impracticable.
1.2 Digital Cash
An ideal payment system would be one in which monetary value could be transferred
electronically via cash data les (Figure 2). Such cash data les retain the advantages of physical
cash but would be able to circulate freely on electronic networks.1 A data le of this type could
be sent via email or social media channels.
A specic feature of electronic data is that it can be copied any number of times at negli-
gible cost. is feature is highly undesirable for money. If cash data les can be copied and
the duplicates used as currency, they cannot serve as a payment instrument. is problem is
termed the “double spending problem.”
1.3 Electronic Payment Systems
To counteract the problem of double spending, classical electronic payment systems are
based on a central authority that veries the legitimacy of the payments and keeps track of
the current state of ownership. In such systems, a central authority (usually a bank) manages
the accounts of buyers and sellers. e buyer initiates a payment by submitting an order. e
Goods
Cash transaction
Buyer Seller
Figure 1
Cash Transaction
Goods
Electronic payment
Buyer Seller
Ctrl C
+
Figure 2
Electronic Payment
Berentsen and Schär
Federal Reserve Bank of St. Louis REVIEW First Quarter 2018 3
central authority then ensures that the buyer has the necessary funds and adjusts the accounts
accordingly (Figure 3).
Centralized payment systems solve the double spending problem, but they require trust.
Agents must trust that the central authority does not misuse the delegated power and that it
maintains the books correctly in any state of the world—that is, that the banker is not running
away with the money. Furthermore, centralized systems are vulnerable to hacker attacks,
technical failures, and malicious governments that can easily interfere and conscate funds.
1.4 Stone Money of Yap
e key feature of the Bitcoin system is the absence of a centrally managed ledger. ere
is no central authority with an exclusive right to keep accounts. In order to understand how
this is possible, we will rst discuss a historical payment system that has certain similarities
with the Bitcoin system.
On Yap Island, large millstone-like stones were used as a medium of exchange.2 e
stones were quarried almost 280 miles away on the island of Palau and brought to Yap by
small boats. Every inhabitant could bring new stone money units into the system. e money
creation costs, in the form of labor eort and equipment such as boats, protected the economy
from ination.
Instead of having to laboriously move the stones, which are up to 13 feet in diameter,
with every transaction from a buyer’s front yard to a seller’s front yard, the ownership rights
were transferred virtually. A stone remained at its original location, and the unit of value could
be detached from it and circulated irrespective of the stone’s whereabouts. It was sucient
that all the inhabitants knew who the owner of every stone was. e separation between the
unit of value and the stone went so far that even the unit of value for stones that were lost at
sea remained in circulation. e stone money of Yap can therefore be described as a quasi-
virtual currency, as each unit of value was only loosely linked to a physical object.
Goods
Payment
Buyer Seller
Bookkeeper
PaymentPayment Balance
Figure 3
Payment System with a Central Authority
Berentsen and Schär
4 First Quarter 2018 Federal Reserve Bank of St. Louis REVIEW
e Yap system was based on a distributed ledger, in which every inhabitant would keep
track of a stone’s ownership. When a buyer made a purchase, this person told his or her neigh-
bors that the stone now belonged to the seller. e neighbors then spread the news until nally
all of the island’s inhabitants had been informed about the change in ownership (Figure 4).
rough this communication, every islander had a precise idea of which unit of value belonged
to which person at any point in time.
In its essential features, the Yap payment system is very similar to the Bitcoin system. A
major dierence is that in the Yap system false reports could not be immediately identied,
so conicts regarding the current state of the implicit ledger would have to be argued and
settled by the group. e Yap system therefore was restricted to a group of manageable size
with close relationships, in which misconduct could be punished by the group. In contrast,
the Bitcoin system is designed to function in a network where no participant can trust any
other participant. is feature is necessary because it is a permissionless payment system in
which participants can remain anonymous through the use of pseudonyms.
1.5 Bitcoin and the Bitcoin Blockchain
Bitcoin is a virtual monetary unit and therefore has no physical representation. A Bitcoin
unit is divisible and can be divided into 100 million “Satoshis,” the smallest fraction of a Bitcoin.
e Bitcoin Blockchain is a data le that carries the records of all past Bitcoin transactions,
including the creation of new Bitcoin units. It is oen referred to as the ledger of the Bitcoin
Goods
Stone ownership
Buyer Seller
Communication
Figure 4
Payment System with a Distributed Ledger
Berentsen and Schär
Federal Reserve Bank of St. Louis REVIEW First Quarter 2018 5
system. e Bitcoin Blockchain consists of a sequence of blocks where each block builds on
its predecessors and contains information about new Bitcoin transactions. e average time
between Bitcoin blocks is 10 minutes. e rst block, block #0, was created in 2009; and, at
the time of this writing, block #494600 was appended as the most recent block to the chain.
Because everyone can download and read the Bitcoin Blockchain, it is a public record, a ledger
that contains Bitcoin ownership information for any point in time.
e word “ledger” has to be qualied here. ere is no single instance of the Bitcoin
Blockchain. Instead, every participant is free to manage his or her own copy of the ledger.
As it was with the stone money, there is no central authority with an exclusive right to keep
accounts. Instead, there is a predened set of rules and the opportunity for individuals to
monitor that other participants adhere to the rules. e notion of “public record of ownership”
also has to be qualied because the owners of Bitcoin units usually remain anonymous through
the use of pseudonyms.
To use the Bitcoin system, an agent downloads a Bitcoin wallet. A Bitcoin wallet is so-
ware that allows the receiving, storing, and sending of (fractions of) Bitcoin units.3 e next
step is to exchange at currencies, such as the U.S. dollar, for Bitcoin units. e most common
way is to open an account at one of the many Bitcoin exchanges and to transfer at currency
to it. e account holder can then use these funds to buy Bitcoin units or one of the many
other cryptoassets on the exchange. Due to the widespread adoption of Bitcoin, the pricing
on large exchanges is very competitive with relatively small bid-ask spreads. Most exchanges
provide order books and many other nancial tools that make the trading process transparent.
A Bitcoin transaction works in a way that is similar to a transaction in the Yap payment
system. A buyer broadcasts to the network that a seller’s Bitcoin address is the new owner of
a specic Bitcoin unit. is information is distributed on the network until all nodes are
informed about the ownership transfer. We will examine some technical details of this step
in Section 2.
For a virtual currency to function, it is crucial to establish at every point in time how
many monetary units exist, as well as how many new units have been created. ere must
also be a consensus mechanism that ensures that all participants agree about the ownership
rights to the virtual currency units. In small communities, as with the Yap islanders, everyone
knows everyone else. e participants care about their reputation, and conicts can be dis-
puted directly. In contrast, within the Bitcoin system the number of participants is substan-
tially larger, and network participants can remain anonymous. Consequently, reputation
eects cannot be expected to have a signicant positive impact, and coordination becomes
very dicult. Instead, there is a consensus mechanism that allows the Bitcoin system to reach
an agreement. is consensus mechanism is the core innovation of the Bitcoin system and
allows consensus to be reached on a larger scale and in the absence of any personal relations.
1.6 Bitcoin Mining
To understand the consensus mechanism of the Bitcoin system, we rst have to discuss
the role of a miner. A miner collects pending Bitcoin transactions, veries their legitimacy,
and assembles them into what is known as a “block candidate.” e goal is to earn newly cre-
Berentsen and Schär
6 First Quarter 2018 Federal Reserve Bank of St. Louis REVIEW
ated Bitcoin units through this activity. e miner can succeed in doing this if he or she can
convince all other network participants to add his or her block candidate to their copies of
the Bitcoin Blockchain.
Bitcoin mining is permissionless. Anyone can become a miner by downloading the respec-
tive soware and the most recent copy of the Bitcoin Blockchain. In practice, however, there
are a few large miners that produce most of the new generally accepted blocks. e reason is
that competition has become erce and only large mining farms with highly specialized hard-
ware and access to cheap electricity can still make a prot from mining.
For a block candidate to be generally accepted, it must fulll a specic set of predened
criteria. For instance, all included transactions must be legitimate. Another important crite-
rion is the so-called “ngerprint” of the block candidate. A miner obtains this ngerprint by
computing the block candidate’s hash value using the hash function dSHA256.
For example, we will look at the hash value for the text, “Federal Reserve Bank of Saint
Louis.” e ngerprint of this text, which was calculated using the hash function dSHA256, is
72641707ba7c9be334f111ef5238f4a0b355481796fdddfdaac4c5f2320eea68.
Now notice the small change in the original text to “federal Reserve Bank of Saint Louis.” It
will cause an unpredictable change of the ngerprint, which can be seen from the correspond-
ing new hash value:
423f5dd7246de6faf8b839c41bf46d303014ca65724ab008431514e36c4dba.
As suggested by this example, a data le’s hash value cannot be prognosticated.
is characteristic is employed in the mining process as follows. For a block candidate to
be accepted by all miners, its ngerprint must possess an extremely rare feature: e hash
value must be below a certain threshold value—that is, it must display several zeroes at the
beginning of the ngerprint. An example of a ngerprint of a block that was added to the
Bitcoin Blockchain in 2010 is given in the following example:
Block #69785 (July 23rd, 2010, 12:09:36 CET)
0000000000
Need to be zero
1 24 34
293b78a2833b45d78e97625 f6484ddd1accbe0067c2b8f98b57995
Miners are continuously trying to nd block candidates that have a hash value satisfying the
above mentioned criterion. For this purpose, a block includes a data eld (called the nonce)
that contains arbitrary data. Miners modify this arbitrary data in order to gain a new nger-
print. ese modications do not aect the set of included transactions. Just as with our
example, every modication results in a new hash value. Most of the time, the hash value lies
above the threshold value, and the miner discards the block candidate. If, however, a miner
succeeds in creating a block candidate with a hash value below the current threshold value,
he or she broadcasts the block candidate as quickly as possible to the network. All the other
network participants can then easily verify that the ngerprint satises the threshold criterion
by computing it themselves.
Berentsen and Schär
Federal Reserve Bank of St. Louis REVIEW First Quarter 2018 7
1.7 Consensus Mechanism
e consensus among miners is that every miner who receives a block candidate with a
valid ngerprint adds it to his or her own copy of the Bitcoin Blockchain. From a game theo-
retical perspective, a strategy prole where all miners add valid blocks to their own copies of
the Bitcoin Blockchain is a Nash equilibrium. If a miner believes that all other miners are act-
ing accordingly, then it is a best response for that miner to add a valid block candidate to his
or her own copy of the Bitcoin Blockchain. A deviation is not worthwhile, because it is not
protable to work on a version of the Bitcoin Blockchain that is not generally accepted. Any
reward for nding blocks on a version of the chain that is not accepted by anyone else is worth-
less. us, although there is no authority enforcing this rule and miners are free to modify
their copy of the Blockchain as they wish, there is a strong incentive to follow this rule. is
self-enforcing rule allows the network to maintain consensus about the ownership of all
Bitcoin units.4
Mining is expensive, as the computations use large amounts of electricity and are increas-
ingly dependent on highly specialized hardware. Moreover, valid block candidates can be
found only through a trial-and-error procedure. e consensus mechanism is therefore called
“proof of work.” If a miner nds a valid ngerprint for a block candidate, then this is proof
that he or she has, on average, performed a large number of costly computations. Adding
false information (e.g., illegitimate transactions) to a block candidate would render the block
candidate invalid and essentially waste all the computations. Finding a valid ngerprint is
therefore proof that the miner helped to maintain the Bitcoin system.
1.8 Monetary Policy
Every payment system needs rules that regulate how new monetary units are produced
(or destroyed). e Bitcoin network is calibrated in such a way that, on average, a block can-
didate with a valid hash value is found every 10 minutes. e winner of the mining contest
receives a predened number of newly created Bitcoin units. e number currently is 12.5.
In the Bitcoin system, money creation is scheduled so that the number of Bitcoin units
will converge to 21 million units (Figure 5). is limit exists because the reward for the miners
is halved every 210,000 blocks (approximately every four years). Correspondingly, miners
will be increasingly rewarded through transaction fees. But even today, the quick processing
of a transaction can be guaranteed only if an adequate fee is paid to incentivize the miners to
include the transaction in their block candidates.
Most Bitcoin users believe that Bitcoin’s limited supply will result in deation. at is,
they are convinced that its value will forever increase. Indeed, up to this point we have wit-
nessed a spectacular price increase from essentially a value of $0 for one Bitcoin unit in 2009
to a value of $7,000 at the time of this writing (Figure 6).
Nonetheless, these beliefs need to be challenged. Bitcoin units have no intrinsic value.
Because of this, the present price of the currency is determined solely by expectations about
its future price. A buyer is willing to buy a Bitcoin unit only if he or she assumes that the unit
will sell for at least the same price later on. e price of Bitcoin, therefore, reacts highly elas-
Berentsen and Schär
8 First Quarter 2018 Federal Reserve Bank of St. Louis REVIEW
2010 2015 2020 2025 2030 2035
0
5
10
15
20
Bitcoins In Circulation (millions)
Figure 5
Bitcoins in Circulation: Scheduled to Converge to 21 Million Units
Price (USD)
2010 2012 2014 2016 2018
6,000
4,000
2,000
0
Figure 6
Market Price in U.S. Dollars (USD) for One Bitcoin Unit
SOURCE: Blockchain.info.
Berentsen and Schär
Federal Reserve Bank of St. Louis REVIEW First Quarter 2018 9
tically to changes in the expectations of market participants and is reected in extreme price
volatility. From monetary theory, we know that currencies with no intrinsic value have many
equilibrium prices.5 One of them is always zero. If all market participants expect that Bitcoin
will have no value in the future, then no one is willing to pay anything for it today.
However, Bitcoin is not the only currency that has no intrinsic value. State monopoly
currencies, such as the U.S. dollar, the euro, and the Swiss franc, have no intrinsic value either.
ey are at currencies created by government decree. e history of state monopoly curren-
cies is a history of wild price swings and failures. is is why decentralized cryptocurrencies
are a welcome addition to the existing currency system.
In the Bitcoin system, the path for the money supply is predetermined by the Bitcoin
protocol written in 2008 and early 2009. Since then, many changes have been applied to the
Bitcoin protocol. Most of these changes are not controversial and have improved the function-
ing of the Bitcoin system. However, in principle all aspects of the Bitcoin protocol can be
amended, including the money supply. Many Bitcoin critics see this as a major shortcoming.
eoretically speaking, this is correct. Any network participant can decide to follow a new set
of rules and, for example, double the amount of newly created “Bitcoin” units in his or her
version of the ledger. Such a modication, however, is of no value because convincing all the
other network participants to follow this new set of rules will be almost impossible. If the
change of the protocol is not supported unanimously, there will be a so-called fork, a split in
the network, which results in two co-existing blockchains and essentially creates a new crypto-
asset. In this case, there would be Bitcoin (the original) and Bitcoin42 (a possible name for an
alternative implementation with an upper bound of 42 million Bitcoin42 units). e market
would price the original and the newly created Bitcoin42 assets according to the community’s
expectations and support. erefore, even though in theory it is possible to increase the Bitcoin
supply, in practice, such a change is very unlikely because a large part of the Bitcoin commu-
nity would strongly oppose such an attempt.
Moreover, the same critique can be raised against any current government-operated at
currency system. For example, since the Second World War, many central banks have become
independent in order to shield them from political interference that yielded some undesirable
outcomes. is independence has been given to them by the respective parliaments or related
institutions and can be taken away if politicians decide accordingly. Political interference in
the at currency system can be interpreted as a change in the “at currency protocol.” Undesir-
able changes in at currency protocols are very common and many times have led to the com-
plete destruction of the value of the at currency at hand. It could be argued that, in some
ways, the Bitcoin protocol is more robust than many of the existing at currency protocols.
Only time will tell.
2 BITCOIN TRANSACTIONS
e complexity of the present material is due to interdisciplinarity. To understand the
Bitcoin system, it is necessary to combine elements from the three disciplines of economics,
cryptography, and computer science (Figure 7).
Berentsen and Schär
10 First Quarter 2018 Federal Reserve Bank of St. Louis REVIEW
Having presented a broad overview of
the Bitcoin system, we will explain a few
technical elements of the system in greater
detail. Blockchain uses proven technologies
and links these in an innovative way. is
combination has made the decentralized
management of a ledger possible for the
rst time.
Berentsen and Schär (2017) argue that
transaction processing demands that three
requirements are satised: (1) transaction
capability, (2) transaction legitimacy, and
(3) transaction consensus. ese three
requirements will now be considered. In
particular, we will explain how these con-
ditions can be satised in the absence of a
central authority.
2.1 Transaction Capability
What has to be resolved is how transactions can be initiated if there is no central authority.
In a classical banking system, a client talks to his or her advisor or submits his or her payment
instructions via the bank’s online banking service. e infrastructure provided by the com-
mercial bank and other central service providers ensures that the transaction will be commu-
nicated for execution. In the absence of a central authority, communicating a payment order
in this traditional sense is not possible.
In the Bitcoin system, a payment order can be communicated to any number of network
nodes. e network nodes are linked together in a loose network and forward the message
until all nodes have been informed about the transaction (Figure 8).
e decentralization of the system has many advantages. In particular, it makes the system
extremely robust. ere is neither a central point of failure that can be attacked nor any system-
relevant nodes that could cause the system to collapse. erefore, the system functions even
when some network nodes are unreachable, and it can always establish new connections and
communication channels.
2.2 Transaction Legitimacy
Every participant can generate new payment orders and spread them across the network.
is feature carries the risk of fraudulent messages. In this respect, there are two important
questions that arise:
1. How do the nodes know that the initiator of the transaction is the rightful owner and
that he or she is thereby entitled to transfer the Bitcoin units?
2. How can one ensure that the transaction message will not be tampered with before it
is passed from one node to the next?
Cryptography
Economics Computer
Science
Figure 7
Interdisciplinarity
Berentsen and Schär
Federal Reserve Bank of St. Louis REVIEW First Quarter 2018 11
Edith
Edith: “I transfer 1 Bitcoin
unit to Daniel.”
Edith’s message is repeated.
Marcia
Brian
Jake
ClaudiaMichèle
Tony
Figure 8
Bitcoin Transaction Communicated to Network Nodes
Edith
Edith: “I transfer 1 Bitcoin
unit to Daniel.”
Manipulation attempt Marcia
Michèle
Tony
Edith: “I transfer 1 Bitcoin
unit to Tony.” Refused!
Figure 9
Bitcoin Transaction Manipulation Attempt
Edith
Edith: “I transfer Bitcoin
unit X to Daniel.”
Transaction A Marcia
Brian
Jake
ClaudiaMichèle
Tony
Edith: “I transfer Bitcoin
unit X to Lucas.”
Transaction B
Figure 10
First Bitcoin Transaction Added to a Valid Block Candidate Is Conrmed
Berentsen and Schär
12 First Quarter 2018 Federal Reserve Bank of St. Louis REVIEW
In the Bitcoin system, transaction legitimacy is guaranteed using asymmetric cryptography.6
e idea is based on using pairs of keys consisting of a private and a public key. A private key
should not be shared. It corresponds to a random value from an incredibly large set of num-
bers. A public key, on the other hand, is derived from that number and can be shared freely.
It serves as a pseudonym in the Bitcoin network.7
A private key is used to encrypt a message that can be decrypted only by using its corre-
sponding public key. is type of encryption is also known as a “signature.” e signature
claries that this approach is not used to hide any of the information in the encrypted message.
Anyone can simply decrypt a message using its public key, but the signature serves as proof
that the message has been previously encrypted using its corresponding private key; it’s like a
handwritten signature but much more secure.
For example, consider Edith, who wants to send a Bitcoin payment to Daniel over the
Bitcoin network. She uses her private key to encrypt the message. e other network partici-
pants can only decrypt this message using Edith’s public key. If an attempt is successful, it
ensures that the message was encrypted using the corresponding private key. Because no one
else has access to Edith’s private key, this approach can be used to validate the transaction’s
origin (Figure 9).
When the transaction circulates in the network, any network participant can decrypt this
message and is in the position to subsequently change the payment instructions. However,
because the participant does not possess Edith’s private key, he or she cannot re-encrypt the
manipulated message. e tampered transaction will therefore be identied and rejected by
the rest of the network.
2.3 Transaction Consensus
We have now discussed how a transaction message is communicated and how its legitimacy
and origin can be veried. We have also explained how consensus regarding ownership of
the Bitcoin units is achieved in the Bitcoin network by using the proof-of-work consensus
protocol.
However, Edith would be able to generate two transactions that both reference the same
Bitcoin units. Both transactions could be propagated simultaneously over the network (trans-
action capability), and both would display a valid origin (transaction legitimacy). Because of
dierences in the propagation of these two messages in the Bitcoin network, some of the nodes
would rst receive a message for transaction A while others would rst receive a message for
transaction B (Figure 10). In order to avoid double spending, it is important that only one of
the two transactions nds its way into the Bitcoin Blockchain. A mechanism that decides
which of the two transactions gets included in the Blockchain is therefore necessary.
e Bitcoin system solves this double spending problem in a clever way. e transaction
that is rst added to a valid block candidate, and therefore added to the Blockchain, is con-
sidered conrmed. e system ceases to process the other one—that is, miners will stop add-
ing the conicting transaction to their block candidates. Moreover, it is not possible for a
miner to add conicting transactions to the same block candidate. Such a block would be
illegitimate and thus be rejected by all the other network participants.
Berentsen and Schär
Federal Reserve Bank of St. Louis REVIEW First Quarter 2018 13
3 OUTLOOK
As with any fundamental innovation, the true potential of blockchain technology will
become apparent only many years, or possibly decades, aer it becomes generally adopted.
Forecasting the areas in which blockchain technology will be used to the greatest eect is there-
fore not possible. We nevertheless would like to mention a few areas where blockchain tech-
nology serves as an infrastructure platform that facilitates a variety of promising applications.
3.1 Cryptoassets
e most apparent application is Bitcoin as an asset. It is likely that cryptoassets such as
Bitcoin will emerge as their own asset class and thus have the potential to develop into an
interesting investment and diversication instrument. Bitcoin itself could over time assume
a similar role as gold. Moreover, the potential for trading securities on a public blockchain is
large. So-called colored coins can be traded on the Bitcoin (or similar) Blockchain and used
in smart contracts, as described below.
3.2 Colored Coins
A colored coin is a promise of payment that is linked to a Bitcoin transaction. is promise
is possible because the communication protocol of the Bitcoin network allows additional
information to be tied to a transaction. For example, promises for the delivery of an ounce
of gold or a dividend payment can be added to a Bitcoin transaction and represented on the
Bitcoin Blockchain. Any of these promises are of course subject to issuer risks and require
some extent of trust. is is in sharp contrast to native cryptoassets such as Bitcoin units.
3.3 Smart Contracts
Smart contracts are self-executing contracts.8 ey can be used to stipulate that a Bitcoin
payment will be executed only when a certain condition is met. e Ethereum network is cur-
rently the leader in the eld of smart contracts. Similar to Bitcoin, it is based on blockchain
technology and provides a native cryptoasset, called Ether. In contrast to Bitcoin, Ethereum
provides a more exible scripting language and is able to track contractual states. Potential
applications include but are not limited to e-voting systems, identity management and decen-
tralized organization, and various forms of fundraising (e.g., initial coin oerings).
3.4 Data Integrity
Another application for public blockchains is the potential to monitor data les. We have
already shown how ngerprints of block candidates play an important role in the Bitcoin
network. e same technology can be used to produce ngerprints for all kinds of data les
and then store them in a blockchain. e entry of a ngerprint into a blockchain ensures that
any manipulation attempt will become apparent because any change to the data le will lead
to a completely dierent hash value. Because it is very dicult to change a blockchain retro-
actively, a ngerprint can serve as proof that a specic data le existed at a specic point in
time and ensures the integrity of the data.
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14 First Quarter 2018 Federal Reserve Bank of St. Louis REVIEW
4 RISKS
Much like any other key innovation, blockchain technology introduces some risks. e
following sections will consider some of these risks. As we mentioned in Section 3, we would
like to note that this list is non-exhaustive.
4.1 Forks
As discussed in Section 1.8, the Bitcoin protocol can be altered if the network participants,
or at least a sucient number of them, agree on the suggested modication. It can happen
(and in fact has happened) that a blockchain splits because various groups cannot agree about
a modication. A split that persists is referred to as a “fork.” e two best-known examples
of persistent splits are the Bitcoin Cash fork and Ethereum’s ideological dissent, which resulted
in the split to Ethereum and Ethereum Classic.
4.2 Energy Wastage
Proof-of-work mining is expensive, as it uses a great deal of energy. ere are those that
criticize Bitcoin and assert that a centralized accounting system is more ecient because con-
sensus can be attained without the allocation of massive amounts of computational power.
From our perspective, however, the situation is not so clear-cut. Centralized payment systems
are also expensive. Besides infrastructure and operating costs, one would have to calculate
the explicit and implicit costs of a central bank. Salary costs should be counted among the
explicit costs and the possibility of fraud in the currency monopoly among the implicit costs.
Moreover, many cryptoassets use alternative consensus protocols, which do not (solely) rely
on computational resources.
4.3 Bitcoin Price Volatility
e price of Bitcoin is highly volatile. is leads us to the question of whether the rigid
predetermined supply of Bitcoin is a desirable monetary policy in the sense that it leads to a
stable currency. e answer is no because the price of Bitcoin also depends on aggregate demand.
If a constant supply of money meets a uctuating aggregate demand, the result is uctuating
prices. In government-run at currency systems, the central bank aims to adjust the money
supply in response to changes in aggregate demand for money in order to stabilize the price
level. In particular, the Federal Reserve System has been explicitly founded “to provide an
elastic currency” to mitigate the price uctuations that arise from changes in the aggregate
demand for the U.S. dollar. Since such a mechanism is absent in the current Bitcoin protocol, it
is very likely that the Bitcoin unit will display much higher short-term price uctuations than
many government-run at currency units.
5 CONCLUSION
e Bitcoin creators’ intention was to develop a decentralized cash-like electronic payment
system. In this process, they faced the fundamental challenge of how to establish and transfer
Berentsen and Schär
Federal Reserve Bank of St. Louis REVIEW First Quarter 2018 15
digital property rights of a monetary unit without a central authority. ey solved this challenge
by inventing the Bitcoin Blockchain. is novel technology allows us to store and transfer a
monetary unit without the need for a central authority, similar to cash.
Price volatility and scaling issues frequently raise concerns about the suitability of Bitcoin
as a payment instrument. As an asset, however, Bitcoin and alternative blockchain-based
tokens should not be neglected. e innovation makes it possible to represent digital property
without the need for a central authority. is can lead to the creation of a new asset class that
can mature into a valuable portfolio diversication instrument. Moreover, blockchain tech-
nology provides an infrastructure that enables numerous applications. Promising applications
include using colored coins, smart contracts, and the possibility of using ngerprints to secure
the integrity of data les in a blockchain, which may bring change to the world of nance
and to many other sectors. n
NOTES
1 An initial attempt was DigiCash in the 1990s; however, it was not able to establish itself.
2 See Furness (1910) who describes the Island of Stone Money.
3 Strictly speaking, Bitcoins are not “traveling” on the Bitcoin network. A Bitcoin payment is simply a message that
is broadcasted to the network to communicate a change in ownership of the respective Bitcoin units.
4 In practice, a split in the Blockchain may occur if the network participants do not agree about changes in the
Bitcoin protocol (i.e., the rule set). This issue is discussed further in this article.
5 See Kiyotaki and Wright (1993) for a search theoretic approach to money, Berentsen (1998) for a study of the
acceptability of digital money, and Nosal and Rocheteau (2011) for a comprehensive introduction into the search
theoretic approach to monetary economics.
6 Similar technologies are also used in traditional electronic payment systems and in many other elds, such as
with online banking and shopping.
7 In fact, a public key is usually used to derive a so-called Bitcoin address. This address is then used as a pseudonym.
We ignored this additional step to keep things as simple as possible. Both operations—that is, private key to public
key and public key to Bitcoin address—are one-way functions. There is no known way to reverse these operations,
so it is not feasible to obtain a private key from a corresponding pseudonym.
8 For an introduction to smart contracts and potential business applications, see Schär and Langer (2017).
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Berentsen, Aleksander and Schär, Fabian. Bitcoin, Blockchain und Kryptoassets: Eine umfassende Einführung. Books
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Furness, William H. The Island of Stone Money: Uap of the Carolines. Philadelphia: J. B. Lippincott, 1910.
Kiyotaki, Nobuhiro and Wright, Randall. “A Search-Theoretic Approach to Monetary Economics.” American Economic
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16 First Quarter 2018 Federal Reserve Bank of St. Louis REVIEW
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