TL;DR
What are CBDCs?
Objectives of CBDCs
CBDC Design
Architecture
Ledger Updates
Access
Interoperability (assuming the use of DLT)
Should CBDCs Bear Interest?
Additional Considerations
Examples of CBDC Projects
The content follows a natural progression, but can also be read in segments and out of order, and is meant to be revisited over time.
A new area of digital finance is forthcoming, with CBDCs being an integral part of it and promising to grow significantly in the coming years. This topic has become highly debated worldwide, which is why we’ll dive into it.
CBDCs are digital representations of government currencies, thus they have a legal tender status. They are often described as digital banknotes, as they are a claim that people have on the central bank (CB). This means that in the CB balance sheet they appear as liabilities, because they represent the currency in circulation.
CBDCs (and cash) differ from commercial banks’ money in that they are not subject to bankruptcy of the private sector and so are free from counterparty credit risk, which provides a higher level of financial security. CBs have historically only served commercial banks, so CBDCs would be the first government backed, and thus safest, digital asset available to the general public. They support offline payments and programmable features typical of cryptocurrencies, but they meet the three functions of money.
Comparison of the functionalities of three forms of currency.
CBDCs can be based on permissioned blockchains or on traditional centralized systems. This highlights the difference between CBDCs and cryptocurrencies; the former rely on third parties such as CBs and commercial banks, the latter is a truly decentralized peer-to-peer system. CBDCs are not meant to substitute any other means of payment but complement those to build a varied payment system.
2 forms of CBDCs exist:
There is no unified objective for CBDCs, as each country is different and aims to tackle various problems with the issuance of a digital sovereign currency. CBs often mention their commitment to providing public goods to their citizens, but other motives have been identified, as detailed below.
The following steps should be considered in order when deciding the CBDC design to be implemented:
It refers to the extent to which the private sector is involved and partners with CBs, and if this happens at all, defining which actors have access to what information.
Indeed, CBDCs can be issued directly by a central bank, or the latter can collaborate with financial service providers to join forces and unite the expertise typical of the public sector (monetary policy) with that of the private one (know-your-customer procedures, payment and customer services).
The 2 main models being considered are:
This model is referred to as Direct because the CB issues, circulates and maintains record keeping of balances and transactions directly. The advantage is that being built independently of the existing payment infrastructure provides resilience to the system, that would remain active even when others fail.
Under this model, the CBDC could be programmed to allow only certain transactions, while forbidding others (e.g., gambling payments or alcohol purchases).
CBs distribute CBDCs via regulated intermediaries (payment service providers - PSPs), a popular route around the world. The more diverse the private intermediaries are, the more competition is created, and thus better options are proposed to users. However, a higher level of coordination is required to define responsibilities and accountability, and the cost of oversight would increase following a more complex system structure.
3 access models fall under this category:
In both cases (one- and two-tier systems) the CB holds the responsibility to provide all economic agents with CBDCs, meaning that in places not covered by PSPs, the CB would have to appoint agent networks such as post offices to include customers in those regions.
Should ledger updates be carried out through a centralized authority or a DLT (Distributed Ledger Technology)?
Peerapong Thonnagith, Assistant Director & Technical Lead of the Digital Currency Team at the Bank of Thailand, explains that if interoperability between CBDCs and other assets is desired, the DLT has more potential because it leverages smart contracts. On the contrary, if privacy matters for the parties involved in a transfer, relying on a centralized authority would be better, considering that DLT fosters transparency by design. Also, if leveraging offline capabilities is the norm for interacting, then he personally believes that the centralized version is more suited, although it does not have an absolute advantage.
Moreover, DLT presents limitations in terms of performance and scalability to handle large retail transaction volumes (although this issue could be addressed soon e.g., using parallelized chains), but it offers greater security and resilience thanks to the use of cryptography and from deploying multiple validating nodes. It also fosters innovation thanks to programmability (complex functionalities such as invoice tokenization and programmable money are achievable using smart contracts).
Jonathan Dharmapalan, CEO of eCurrency, adds that a DLT is insufficient for managing a bearer instrument, explaining that it has drawbacks at the security layer associated with asymmetric keys, as they are prone to quantum computing attacks. The use of the Digital Symmetric Core Currency Cryptography (DSC3) is required to protect the currency instrument itself (the core of the currency) and operationalize CBDCs. If this is done, a DLN (Distributed Ledger Network) is per se not needed to distribute the currency. Similarly, Geoffrey Goodell, Lecturer at the University College London, says that a DLT is not used to ensure integrity of a bearer instrument, but it is needed to avoid a single point of failure and to ensure that the parties that manage transactions are not going to misbehave.
The options being considered are whether to implement access through accounts tied to an identity (account-based access), or by demonstrating possession of a private key that corresponds to a public key (token-based access). The former is considered posing the biggest risks to both personal and economic freedom, the latter causes risks to keys management. This decision affects anonymity & privacy, that will be explained below.
Account-based access:
It refers to accounts held at the CB or another centralized authority, which needs to have access to both account-holders' information and transactions data because CBDCs are a liability of CBs. As a consequence, governments might have access to such data, which would introduce new human rights threats to consumers.
In a one-tier model, the CB holds accounts directly, so these risks are at their highest in this scenario. User interface applications can be linked to the CB directly, or to the PSP’s systems.
In a two-tier model, design choices and different levels of decentralization can minimize the above-mentioned issues:
In both cases, user interface applications access the PSP’s systems and the PSP’s back-end systems communicate with the CB system.
For the scope of AML/CTF compliance, account holders’ identities are checked when the accounts are opened.
Token-based access:
A CBDC is issued in the form of a digital token on DLTs that works by transferring ownership in the system, without needing to reconcile databases.
The Future Infrastructure for Retail Remittances (FIRE) project by everis, a consultancy that is part of the NTT DATA Group, the British Standards Institution (BSI), Bank of England (BoE), University College London (UCL), and the University of Edinburgh, focuses on developing a cash-like payment mechanism for the digital world, not because they wish to substitute cash with CBDCs, but because they are aware that cash is a disappearing payment option (consumers increasingly use digital payments) and that its infrastructure carries high fixed costs.
The key point of token-based access is avoiding the risk of profiling (knowing how consumers spend their money and collecting data to build a transaction history), while allowing AML/KYC procedures. To do so, it is necessary to decouple users’ identities from their transactions, thus breaking the link between the identity of a sender and the recipient, the size of a transaction, the metadata, and other transactions carried out by the same sender. To achieve this goal, the use of a bearer instrument (token) is crucial, together with the use of a non-custodial wallet. A non-custodial wallet enables users to manage public and private keys autonomously and ensures that assets are under the users’ possession, instead of having a gatekeeper holding them on their behalf.
The key characteristic of a non-custodial wallet is not being identifiable which, as explained by UCL Professor Goeffrey Goodell in the presentation he gave at the International Telecommunication Union (ITU) on 25 January 2022, in turn means that it:
Privacy Enhancing Technologies (PETs) can help build a system that is private by design for consumers. The FIRE project proposes the use of blind signatures, as Zero-Knowledge Proofs are considered heavy weight and could impact the system performance. They also suggest employing a two-tiered model, whereby the private sector runs the system, and the CB oversees operations.
The system would work as follows:
Illustration of a potential CBDC architecture.
This system allows clearing and settlement by the private sector, preserving the existing two-tiered model, and it protects users from profiling through privacy by design. Indeed, regulators know only one of the parties to each transaction, usually the recipient, while the sender remains anonymous. However, in order for the sender to remain anonymous, she/he must create the asset herself/himself (like in the procedure described above). Indeed, private actors cannot exchange value between private wallets (chained transactions) if transactions are not subject to control at the interface with payment service providers. Hence, holders of payer and payee accounts are known but using the non-custodial wallet prevents regulators from seeing that money has flowed between them.
Interoperability of CBDC is intended with both the existing payment instruments and their infrastructure (legacy systems), and other CBDC belonging to foreign jurisdictions (cross-border transactions).
Legacy systems:
To foster interoperability with existing legacy systems, oracles could be employed to push and verify off-chain data to the blockchain.
Cross-border transactions:
Following an analysis of interoperability techniques used in cryptocurrencies where sidechains (relay, centralized and federated two-way pegs), hash time locked contracts, blockchain of blockchain, and hybrid connectors (trusted relay, blockchain agnostic protocol, blockchain migrator) were compared, it can be argued that the best technique to foster interoperability between heterogeneous CBDC is using trusted DLT-relays with decentralized escrow parties.
Moreover, the literature produced by CBs highlights that there are different degrees of interoperability among CBDC’s blockchains:
It leads to the alignment of legal and regulatory regimes, thanks to compatible technical and encryption standards.
A common technical interface or a common clearing mechanism are used.
Several currencies run on the same ledger, thus using the same rulebook and governance arrangements.
This decision is strictly related to monetary policy objectives of each CB and the role that CBDCs have in each jurisdiction (digital cash or alternative to deposits). For instance, a negative interest on CBDCs accounts would stimulate spending, as users would have to pay the CB for holding their CBDC.
Most CBs are planning to issue their CBDC with no interest at first, and later on decide on the best course of action.
Defining the difference between anonymity and privacy is crucial to solve the payment privacy paradox in retail CBDCs (whereby users require privacy but also wish to maintain compliance with AML/CFT regulations).
Anonymity is unconditional and, in computer science, it refers to pseudonymity together with un-linkability. The former is a middle ground between using a real name and using no name at all to initiate transactions, the latter refers to the unfeasibility to tie different transactions to one another, blocking any pattern of behaviour from emerging over time (Narayanan et al., 2016).
Privacy is often confused with transaction confidentiality, which is considered conditional because the link is hidden by a third party, and it is not disclosed unless there are reasons to believe that the law has been broken. Instead, privacy prevents individuals from revealing personal information in the first place.
It is argued that central banks are better positioned than other financial services intermediaries to ensure privacy, due to a lack of profit motive to exploit data. They say they would use it for macro-economic policy related analysis or to maintain a CBDC system backup (recall the intermediated architecture explained above). On the contrary, such data could be used by the private sector to study users’ preferences and build tailored products for them, which is why it is argued that a too elevated level of privacy would hinder private sector innovation.
The design of CBDCs has implications for the trade-off between privacy, anonymity and financial integrity. This is probably the most debated aspect of CBDCs because important factors such as legal & human rights, and compliance with AML/CTF need to be considered.
As explained above, transaction confidentiality or data protection can be ensured when transactions are not anonymous by leveraging a two-tier architecture. Indeed, PSPs can be legally forbidden to share any personal details of their users, unless in specific circumstances, as required by the law. This could be done by storing pseudonyms in the core ledger, that can be linked to identities only by PSPs. However, trust in the incorruptibility of the institutions involved is a prerequisite for this system to work.
The argument of people wishing for anonymity to be a design feature is (often) to achieve the level of privacy that we already have in traditional banking. However, this is true only for cash, as transactions carried out with commercial bank money are tied to our identity, and the intermediaries charged with KYC procedures and other regulatory requirements have access to such information. In fact, the governor of the People’s Bank of China (PBoC) explains that, to find a balance between privacy protection and crime prevention, the PBoC will only collect the minimum required amount of personal information, making CBDCs more private than commercial banks’ money in use today. Note that the comparison here is made between commercial money and CBDCs, rather than between cash and CBDCs. Indeed, wishing that CBDCs had the anonymity that characterizes cash can be considered a category error, as things with different underlying characteristics are being compared (this is not to say that CBDCs and deposit money present the same features; in fact, they are fundamentally different due to the claim they represent, the former on CBs and the latter on intermediaries, but it is a better comparison in the context of privacy). Similarly, the Fed writes that programmable money is a new product category that can be used to complement existing money products (Lee, 2022).
Moreover, concerns have been raised about the motives of central banks/governments curiosity to explore CBDCs – mainly rooted in privacy, surveillance, and centralization of control (Chandler, 2022). For instance, consumers' data could be used to identify members of certain political parties, religious and social groups, rebellious and any other individual considered a threat to the state. Also, governments could limit consumers’ spending to what they deem appropriate, thanks to programmability.
Regarding programmability, China has been criticized for developing a digital yuan that is programmable in the sense that they can set deadlines on its spending, a kind of behaviour that, is argued, could be embraced by not-liberal countries. However, the Bank of Canada finds that adding an “expiry date” to offline CBDCs encourages user adoption because unspent offline balances are reimbursed after the deadline has expired. Similarly, the BIS refers to actions such as limiting CBDC holdings or transactions, having different access criteria for diverse levels of users' identification, and making certain choices about CBDC remuneration, as safeguards that could be built into CBDCs to address financial stability risks. However, they anticipate potential obstacles to public understanding and thus acceptance, which could explain the attacks on China on this front.
Further, the argument of people that consider privacy a better option is to safeguard financial integrity and disincentivise criminal activities. A very extreme example is provided by David Birch’s in his book Before Babylon, beyond bitcoin where he hypothesizes that a public ledger could record bets that people make on when hated public figures will die, allowing the winner to collect a quantity of untraceable digital money that varies based on how much the person in question is hated by the public. In other words, an anonymous digital currency would make it easier for criminals to make and receive payments, in turn supporting their wrongdoings, by allowing them to move capital around.
Both arguments have value, and at the end of the day design choices depend on the specific objectives set by the CB and on the issues that each jurisdiction wishes to tackle. Thus, depending on whether CBDCs are thought of as a substitute for cash or as a new means of payment to complement the ones already in existence, anonymity and privacy will play different roles and one will be preferred over the other. There is no one size fits all. Importantly, these decisions should be taken on the basis of their underlying principles, rather than technology. In simple terms this means that governments should not require users’ identification just because the technologies available today allow them to.
Different digital wallets are offered to users, depending on the strength of personal information identification they provide.
Digital yuan wallets have multiple tiers; the small tier only requires a phone number to initiate transactions while, to transact larger values, conventional proof of identity is needed. This ensures anonymity in small value payments (approximately \$300), and traceability in larger value ones.
Following the introduction of the Personal Information Protection Law (effective since November the 1st 2021), in case illegal activities were suspected, a legal warrant would have to be presented to uncover the identity of the suspect, as telecom companies are forbidden from releasing any personal information to anyone, including the CB and government.
The Director General of China’s central bank Digital Currency Research Institute rejects the accusation that CBDC is a tool to monitor payments, explaining that China is already able to do that through other means of payment. Indeed, since 2018 barcode and online payments via WeChat Pay and Alipay wallets, which require identification at onboarding, must be cleared via, respectively, UnionPay, the Chinese state-owned card issuer, and NetsUnion Clearing, set up by the People’s Bank of China.
This shows that eCNY (electronic Chinese Yuan) collects a smaller amount of information compared to other electronic means of payment. Moreover, privacy is fostered by the sub wallet function, which allows a main wallet holder to open multiple sub-wallets that have a separate identity attached to them, to make it harder for tech firms to identify spending patterns among sub-wallets.
The Digital Currency and Electronic Payment (DC/EP) Project (digital Yuan):
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The e-Krona Project:
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Project m-CBDC Bridge. Started off as project Inthanon-LionRock, which comprised 2 phases. Phase 3 was renamed into m-CBDC Bridge.
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Project Aurum
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Project Jura, part of a series of CBDC experiments announced by the Bank of France in July 2020
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Similarly, the BdF, HSBC, and IBM tested multi-ledger CBDC transactions to demonstrate the possibility to interoperate among CBDCs residing on different chains (IBM’s Hyperledger Fabric and R3’s Corda in this case).
Project Dunbar
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Project Jura - Cross-border settlement using wholesale CBDC (bis.org)
Project Dunbar: international settlements using multi-CBDCs (bis.org)
Two-tier distribution model of retail CBDC (bis.org)
Calabro_CFO Insights_121416 (deloitte.com)
A trusted and secure European e-ID - Regulation | Shaping Europe’s digital future (europa.eu)
DSC3 - Digital Symmetric Core Currency Cryptography
(1) The Risks to Society of Central Bank Digital Currencies (CBDC) | LinkedIn
Digital Yuan Ready for International Olympic Showcase at Beijing 2022 Games (cryptonews.com)
WeChat Pay Interoperability is Another Key Breakthrough for Digital Yuan Pilot (cryptonews.com)
Chinese governor says CBDC must balance privacy and anti-crime measures - Central Banking
Central Bank Digital Currency : Background Technical Note (worldbank.org)
20210910_CBDC_report_E_exsum.pdf (ourhkfoundation.org.hk)
Money and Payments: The U.S. Dollar in the Age of Digital Transformation (federalreserve.gov)
Central bank digital currencies - executive summary (bis.org)
The Fed - What is programmable money? (federalreserve.gov)
unlocking-120-billion-value-in-cross-border-payments.pdf (smallake.kr)
DC³ Conference - From Cryptocurrencies to CBDCs -Opening session: - YouTube
DC³ Conference - From Cryptocurrencies to CBDCs -Central Bank Digital Currency Track - YouTube
CBDC - System design and interoperability (bis.org)
Multiple CBDC (mCBDC) Bridge (bis.org)
Book: Cashless, China’s digital currency revolution by Richard Turrin
[2110.13840] A Scalable Architecture for Electronic Payments (arxiv.org)
SP-20_0.pdf (systemicrisk.ac.uk)
This document was authored by Matilde Faro during her internship.