Central bank cryptocurrencies

New cryptocurrencies are emerging almost daily, and many interested parties are wondering whether central banks should issue their own versions. But what might central bank cryptocurrencies (CBCCs) look like and would they be useful? This feature provides a taxonomy of money that identifies two types of CBCC - retail and wholesale - and differentiates them from other forms of central bank money such as cash and reserves. It discusses the different characteristics of CBCCs and compares them with existing payment options.¹

JEL classification: E41, E42, E51, E58.

In less than a decade, bitcoin has gone from being an obscure curiosity to a household name. Its value has risen - with ups and downs - from a few cents per coin to over $4,000. In the meantime, hundreds of other cryptocurrencies - equalling bitcoin in market value - have emerged (Graph 1, left-hand panel). While it seems unlikely that bitcoin or its sisters will displace sovereign currencies, they have demonstrated the viability of the underlying blockchain or distributed ledger technology (DLT). Venture capitalists and financial institutions are investing heavily in DLT projects that seek to provide new financial services as well as deliver old ones more efficiently. Bloggers, central bankers and academics are predicting transformative or disruptive implications for payments, banks and the financial system at large.²

Lately, central banks have entered the fray, with several announcing that they are exploring or experimenting with DLT, and the prospect of central bank crypto- or digital currencies is attracting considerable attention. But making sense of all this is difficult. There is confusion over what these new currencies are, and discussions often occur without a common understanding of what is actually being proposed. This feature seeks to provide some clarity by answering a deceptively simple question: what are central bank cryptocurrencies (CBCCs)?

To that end, we present a taxonomy of money that is based on four key properties: issuer (central bank or other); form (electronic or physical); accessibility (universal or limited); and transfer mechanism (centralised or decentralised). The taxonomy defines a CBCC as an electronic form of central bank money that can be exchanged in a decentralised manner known as peer-to-peer, meaning that transactions occur directly between the payer and the payee without the need for a central intermediary.³ This distinguishes CBCCs from other existing forms of electronic central bank money, such as reserves, which are exchanged in a centralised fashion across accounts at the central bank. Moreover, the taxonomy distinguishes between two possible forms of CBCC: a widely available, consumer-facing payment instrument targeted at retail transactions; and a restricted-access, digital settlement token for wholesale payment applications.⁴

But what might the two types of CBCC offer that alternative forms of central bank money cannot? For the consumer-facing kind, we argue that the peer-to-peer element of the new technology has the potential to provide anonymity features that are similar to those of cash but in digital form. If anonymity is not seen as important, then most of the alleged benefits of retail CBCCs can be achieved by giving the public access to accounts at the central bank, something that has been technically feasible for a long time but which central banks have mostly stayed away from.

On the wholesale side, the assessment of CBCCs is quite different. Wholesale payments today do not offer cash-like anonymity. In particular, transactions that occur in wholesale systems are visible to the central operator. Hence, the case for wholesale CBCCs depends on their ability to improve efficiency and reduce settlement costs. Here, the answer depends on a number of technical issues that still need to be resolved. Some central banks have experimented with wholesale CBCCs, but none has announced yet that it is ready to adopt this technology.

The first section presents the taxonomy underlying our definition. The following two sections discuss the features of the two basic CBCC types, retail and wholesale, drawing on historical examples and projects that are currently under way. A concluding section reflects on some of the issues that central banks need to consider in this area going forward.

A new form of central bank money

Our starting point for defining CBCCs is a report on cryptocurrencies published in 2015 by the Committee on Payments and Market Infrastructures (CPMI (2015)).⁵ This report sought to provide a definition of the new class of currencies represented by bitcoin and altcoins (alternatives to bitcoin) that had emerged using the same technology. The report identifies three key characteristics of cryptocurrencies: they are electronic; are not the liability of anyone; and feature peer-to-peer exchange.⁶

Cryptocurrencies utilise DLT (Box A) to allow remote peer-to-peer transfer of electronic value in the absence of trust between contracting parties. Usually, electronic representations of money, such as bank deposits, are exchanged via centralised infrastructures, where a trusted intermediary clears and settles transactions. Previously, peer-to-peer exchange was restricted to physical forms of money.

Some - but not all - of these features are also common to other forms of money (Graph 2, left-hand panel). Cash is peer-to-peer, but it is not electronic, and it is a central bank liability. Commercial bank deposits are a liability of the bank that issues them. Nowadays, they are in electronic form and are exchanged in a centralised manner either across the books of a given bank or between different banks via the central bank. Most commodity monies, such as gold coins, may also be transferred in a peer-to-peer fashion but are neither the liability of anyone nor electronic.⁷

It may seem natural to define CBCCs by adapting the CPMI's definition to say that they are electronic central bank liabilities that can be used in peer-to-peer exchanges. But this ignores an important feature of other forms of central bank money, namely accessibility. Currently, one form of central bank money - cash - is of course accessible to everyone, while central bank settlement accounts are typically available only to a limited set of entities, mainly banks (CPSS (2003, p 3)). In this spirit, Bjerg (2017) includes universally accessible (ie easy to obtain and use) in addition to electronic and central bank-issued in defining the new concept of central bank digital currency (Graph 2, right-hand panel).

We combine the properties discussed in CPMI (2015) and Bjerg (2017) to establish a new taxonomy of money. Our properties are: issuer (central bank or other); form (electronic or physical); accessibility (universal or limited); and transfer mechanism (centralised or decentralised, ie peer-to-peer). This taxonomy reflects what appears to be emerging in practice and distinguishes between two potential types of CBCC, both of which are electronic: central bank-issued and peer-to-peer. One is accessible to the general public (retail CBCC) and the other is available only to financial institutions (wholesale CBCC). Again, a Venn diagram is useful for illustration.⁸ The four-ellipse version in Graph 3, which we call the money flower, shows how the two potential types of CBCC fit into the overall monetary landscape.

In principle, there are four different kinds of electronic central bank money: two kinds of CBCCs (the shaded area) and two kinds of central bank deposits. The most familiar forms of central bank deposits are those held by commercial banks - often referred to as settlement accounts or reserves. The other form is, at least in theory, deposits held by the general public. Tobin (1987) refers to this form as deposited currency accounts (DCAs).⁹ So far, central banks have generally chosen not to provide DCAs.

Universally accessible forms of money that are not issued by the central bank include (privately created) cryptocurrency, commodity money, commercial bank deposits and mobile money.¹⁰ Cryptocurrency borders CBCC given that only one of its properties differs. The other three currency forms are more removed because they are, in addition, either physical or "not peer-to-peer". A number of other forms of money are not universally accessible. Local (physical) currencies, ie currencies that can be spent in a particular geographical location at participating organisations, populate the right-hand petal of the flower. The upper left-hand petal contains virtual currencies, which are "electronic money issued and usually controlled by its developers, and used and accepted among the members of a specific virtual community" (ECB (2012)). There is also the possibility of a private sector wholesale version of cryptocurrency. It would be transferred in a peer-to-peer fashion by means of a distributed ledger, but only between certain financial institutions.

Box B uses this taxonomy to classify different examples of money from the past, present and future according to where they would fit in the money flower. The remainder of this feature discusses the two types of CBCC in further detail and highlights some of the many issues central banks will need to consider if they ever chose to adopt them. We start with the retail variant and then turn to the wholesale one.

Retail central bank cryptocurrencies

Retail CBCCs do not exist anywhere. However, the concept of a retail CBCC has been widely discussed by bloggers, central bankers and academics. Perhaps the most frequently discussed proposal is Fedcoin (Koning (2014, 2016), Motamedi (2014)).¹¹ As discussed in Box B, the idea is for the Federal Reserve to create a cryptocurrency that is similar to bitcoin. However, unlike with bitcoin, only the Federal Reserve would be able to create Fedcoins and there would be one-for-one convertibility with cash and reserves. Fedcoins would only be created (destroyed) if an equivalent amount of cash or reserves were destroyed (created) at the same time. Like cash, Fedcoin would be decentralised in transaction and centralised in supply. Sveriges Riksbank, with its eKrona project, appears to have gone furthest in thinking about the potential issuance of a retail CBCC (Box C).

A retail CBCC along the lines of Fedcoin would eliminate the high price volatility that is common to cryptocurrencies (Graph 1, centre panel).¹² Moreover, as Koning (2014) notes, Fedcoin has the potential to relieve the zero lower bound constraint on monetary policy. As with other electronic forms of central bank money, it is technically possible to pay interest on a DLT-based CBCC. If a retail CBCC were to completely replace cash, it would no longer be possible for depositors to avoid negative interest rates and still hold central bank money.

Any decision to implement a retail CBCC would have to balance potential benefits against potential risks. Bank runs might occur more quickly if the public were able to easily convert commercial bank money into risk-free central bank liabilities (Tolle (2016)). There could also be risks to the business models of commercial banks. Banks might be disintermediated, and hence less able to perform essential economic functions, such as monitoring borrowers, if consumers decided to forgo commercial bank deposits in favour of retail CBCCs. These benefits and costs are, however, not unique to retail CBCCs. They are the same for DCAs. What, then, is the key difference between retail CBCCs and DCAs? The answer lies with the peer-to-peer aspect of CBCCs and, more specifically, with anonymity.

Anonymity

Bitcoin was designed to be a "peer-to-peer version of electronic cash" (Nakamoto (2009, p 1), and this allows transactions to be anonymous. All bitcoin transactions are publicly recorded using the payer's and the payee's public addresses.¹³ However, very much like e-mail addresses, bitcoin public addresses do not need to reveal the true identity of users.¹⁴ This means that a person sending bitcoin to a public address need not reveal his/her true identity to the recipient (counterparty anonymity) or to other members of the Bitcoin community (one form of third-party anonymity).¹⁵

Kahn et al (2005) and McAndrews (2017) emphasise legitimate reasons for counterparty anonymity in transactions. Payees and payers may want to reduce the risk of identity theft, the possibility that the counterparty might follow them home and rob them, or more innocuous annoyances like directed advertising and solicitations (spamming). Similarly, a lack of third-party anonymity may be regarded as revealing too much information about a person's private activities. In his proposal for Digicash, David Chaum (1983) makes this argument by pointing out that "knowledge by a third party of the payee, amount, and time of payment for every transaction made by an individual can reveal a great deal about the individual's whereabouts, associations and lifestyle".¹⁶

Counterparty anonymity seems less controversial than third-party anonymity. Many observers have argued that third-party anonymity in payments should not be allowed because it facilitates criminal activity, such as tax evasion, terrorist financing or money laundering. Rogoff (2016) argues that $100 bills should be removed from circulation for the same reasons.

It is unclear how much consumers actually value anonymity of either sort in order to protect their privacy. Athey et al (2017) look at how much effort people make to protect their privacy in relation to digital currencies. In an experimental setting, they find that subjects, in general, do not devote the small amount of time needed to read through the e-wallet description that is necessary to meet their own stated preferences for privacy. Similar findings emerged from a survey of economics students at the University of California, Santa Barbara, on usage of Venmo (a digital wallet with social media features). Of the 669 respondents, 80% were users. Of these users, 44% allowed their Venmo transactions to be public (visible to everyone on the internet) and another 21% allowed all of their Facebook friends to see their transactions. Finally, while Digicash is regarded as a precursor to bitcoin, there may not have been sufficiently high demand for the third-party anonymity it provided as it was never widely adopted. It filed for bankruptcy in 1998.¹⁷

The technology behind CBCCs could allow central banks to provide a digital cash substitute with anonymity properties similar to those of cash. In its role as issuer, the central bank would need to decide whether or not to require customer information (the true identity behind the public address). This would determine the extent to which the retail CBCC would provide third-party anonymity.

While it may look odd for a central bank to issue a cryptocurrency that provides anonymity, this is precisely what it does with physical currency, ie cash. Perhaps a key difference is that, with a retail CBCC, the provision of anonymity becomes a conscious decision. It is worth recalling that the anonymity properties of cash are likely to have emerged out of convenience or historical happenstance rather than intent.

Wholesale central bank cryptocurrencies

While CBCCs for retail payments remain at the conceptual stage, some central banks have completed proofs of concept for DLT-based applications.¹⁸ One of the reasons for the interest in DLT is that many central bank-operated wholesale payment systems are at the end of their technological life cycles. The systems are programmed in obsolete languages or use database designs that are no longer fit for purpose and are costly to maintain.

Projects Jasper and Ubin

Project Jasper at the Bank of Canada (Chapman et al (2017)) and Project Ubin at the Monetary Authority of Singapore (MAS (2017)) simulate real-time gross settlement (RTGS) systems on a DLT platform. In an RTGS system, payments are processed individually, immediately and with finality throughout the day (CPSS (1997)).

Unlike the retail payment applications discussed above, wholesale systems have restricted access, ie they are permissioned rather than permission-less. Usually, access is restricted to financial institutions. Moreover, the costly proof-of-work validation (Box A) needed to prevent double-spending in retail schemes is replaced by less energy-consuming alternatives, such as a trusted notary (eg the central bank).

A key challenge in any CBCC application is how to transfer central bank money to the distributed ledger.¹⁹ Both Jasper and Ubin chose a digital depository receipt (DDR) approach. A DDR is a claim on central bank reserves held in a segregated account against which the central bank issues digital tokens on the distributed ledger. In Jasper, the digital tokens - initially known as CADcoins²⁰ - are created at the beginning of the day and redeemed at the end. In Ubin, banks acquire or redeem digital tokens at any point during the day and can keep them on the distributed ledger overnight. Hence, transfers on the DLT platform of the Singaporean proof of concept are not restricted to the opening hours of MAS.

Project Jasper also implements a liquidity-saving mechanism (LSM) on the DLT platform. While RTGS systems minimise settlement risk, they can be demanding in terms of liquidity. Consequently, many RTGS systems around the world are augmented by mechanisms that periodically seek to offset payments against each other in a queue and settle only the net amounts (Bech and Soramäki (2001)). Distributed ledgers are decentralised, so implementation of a centralised queue requires a clever work-around (Project Jasper (2017)).

The two projects show that central bank money can be transferred on a distributed ledger in real time, in realistic volumes and with an LSM. Nevertheless, none of the current initiatives to update or replace existing wholesale payment systems are considering the adoption of DLT. Both the Bank of England (2017) and Bank of Canada (Ho (2017)) conclude that DLT is not yet mature enough for current adoption. Yet most central banks that are considering modernising their core payment infrastructure stress the need to make new systems inter-operable with future DLT platforms.

Securities settlement

Looking beyond the immediate horizon, many industry participants see significant potential for DLT to increase efficiency and reduce reconciliation costs in securities clearing and settlement.²¹ One potential benefit of DLT-based structures is immediate clearing and settlement of securities, in contrast to the multiple-day lags that currently exist when exchanging cash for securities (and vice versa).²² Progress in this direction was recently achieved by a joint venture between the Deutsche Bundesbank and Deutsche Börse, which developed a functional prototype of a DLT-based securities settlement platform that achieves delivery-versus-payment settlement of digital coins and securities (Deutsche Bundesbank (2016)).

Conclusion

As it stands, cash is the only means by which the public can hold central bank money. If someone wishes to digitise that holding, he/she has to convert the central bank liability into a commercial bank liability by depositing the cash in a bank. A CBCC would allow consumers to hold central bank liabilities in digital form.²³ But this would also be possible if the public were allowed to have central bank accounts, an idea that has been around for a long time.²⁴ We argue that the main benefit that a consumer-facing retail CBCC would offer, over the provision of public access to (centralised) central bank accounts, is that the former would have the potential to provide the anonymity of cash. In particular, peer-to-peer transfers allow anonymity vis-à-vis any third party. If third-party anonymity is not of sufficient importance to the public, then many of the alleged benefits of retail CBCCs can be achieved by giving broad access to accounts at the central bank.

Whether or not a central bank should provide a digital alternative to cash is most pressing in countries, such as Sweden, where cash usage is rapidly declining. But all central banks may eventually have to decide whether issuing retail or wholesale CBCCs makes sense in their own context. In making this decision, central banks will have to consider not only consumer preferences for privacy and possible efficiency gains - in terms of payments, clearing and settlement - but also the risks it may entail for the financial system and the wider economy, as well as any implications for monetary policy (Bordo and Levin (2017)). Some of the risks are currently hard to assess. For instance, at present very little can be said about the cyber-resilience of CBCCs, something not touched upon in this short feature.

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¹ The views expressed in this article are those of the authors and do not necessarily reflect those of the BIS. We thank Claudio Borio, Stijn Claessens, Benjamin Cohen, Dietrich Domanski, Hana Halaburda, Krista Hughes, Jochen Schanz and Hyun Song Shin for comments as well as Aleksander Berentsen, James Chapman and Paul Wong for insightful discussions. We are grateful to Codruta Boar for excellent research assistance.

² See Andolfatto (2015, 2016), Broadbent (2016), Raskin and Yermack (2016) and Skingsley (2016).

³ The purest form of peer-to-peer transaction is a cash exchange. On a computer network, the peer-to-peer concept means that transactions can be processed without the need for a central server.

⁴ It is common to divide payments into retail and wholesale segments. Retail payments are relatively low-value transactions, in the form of eg cheques, credit transfers, direct debits and card payments. By contrast, wholesale payments are large-value and high-priority transactions, such as interbank transfers. The distinction might become less relevant in a world with CBCCs. In that case, our usage would reflect the types of payment primarily targeted by CBCCs.

⁵ The report's title is Digital currencies, but it notes that such schemes are frequently also referred to as "cryptocurrencies", reflecting the use of cryptography in their issuance and their validation of transactions.

⁶ Cryptocurrencies have no intrinsic value and are only held in the belief that they might be exchanged for goods or services at a later point in time.

⁷ In the Middle Ages, payments at times required the services of a money changer to assay and value the coins being used.

⁸ A four-circle Venn diagram covers only 14 of the 2⁴ = 16 possible combinations. Hence, in the case of four sets, Venn (1881) suggested using ellipses in order to show all cases.

⁹ In a 1987 speech, Nobel laureate James Tobin argued that, in order to avoid relying too heavily on deposit insurance to protect the payment system, central banks should "make available to the public a medium with the convenience of deposits and the safety of currency, essentially currency on deposit, transferable in any amount by check or other order" (Tobin (1987, p 6); see also Tobin (1985)). That is, people should be able to store value without being subject to the risk of bank failure.

¹⁰ Mobile money is an electronic wallet service that allows users to store, send and receive money using their mobile phones. The value stored in the wallets may be liabilities of the service provider or claims on money held in trust at a commercial bank.

¹¹ The Federal Reserve has not endorsed or officially commented on the proposal.

¹² See Yermack (2015), Bolt and van Oordt (2016) and Garratt and Wallace (2016) for discussions relating to digital currencies and price volatility.

¹³ Luther and Olson (2015) argue that bitcoin is a practical application of what is termed "memory" in the monetary economics literature. Kocherlakota (1998) shows that both money and memory are devices capable of facilitating exchange. Memory can, however, implement more allocations than money, so that money can be viewed as a form of memory but not the other way around.

¹⁴ See Nakamoto (2009, Section 10).

¹⁵ Third-party anonymity means that a person's true identity is not revealed to anyone not directly involved in a transaction. In more general applications, this would include a system operator.

¹⁶ Digicash was launched in the 1990s as a means of transferring bank deposits from one customer to another without revealing the payer's identity to his/her bank (ie it provided third-party anonymity). It did this by using cryptographic techniques to create a pool of untraceable Digicash from customer deposits. Digicash is interesting in that it provided third-party anonymity without requiring autonomy from commercial banks. Commercial banks still held and transferred the deposits held by customers using the Digicash scheme.

¹⁷ One potential reason for its lack of success is that it did not provide autonomy from a central authority. Nick Szabo's proposal for "bit gold" offers an autonomous version of e-gold that uses proof-of-work chains. Bit gold represents a big step in the evolution of digital cash towards bitcoin (https://unenumerated.blogspot.ch/2005/12/bit-gold.html).

¹⁸ Central banks have not limited themselves to wholesale payment applications of DLT. The Hong Kong Monetary Authority (HKMA) has developed proofs of concept for trade finance and mortgage loan applications in collaboration with industry participants (HKMA (2016)). The Bank of France has developed a DLT version of its Single European Payments Area (SEPA) Creditor Identifier database (Bank of France (2016)).

¹⁹ The CPMI-IOSCO Principles for Financial Markets Infrastructures hold that settlement should occur in central bank money whenever practical and available.

²⁰ See Garratt (2016).

²¹ Mainelle and Milne (2016) estimate that synchronised share databases can reduce back office costs by up to 50%. A study led by Santander InnoVentures (2015) estimates that $15-20 billion could be saved annually in the broader banking industry.

²² Through the use of smart contracts, the technology also allows for the settlement time/date of a transaction to be specified by the relevant parties.

²³ One simple reason why a consumer might want to do this is to avoid the credit risk associated with commercial bank liabilities.

²⁴ Who should and should not have access to central bank money is a recurring policy issue. See CPSS (2003), CGFS (2015) and Bank of England (2017) for more detailed discussions.