Digital Euro: Frequently Asked Questions Revisited

Technical Summary: Digital Euro: Frequently Asked Questions Revisited

Problem Statement
The European Central Bank (ECB) is developing a retail Central Bank Digital Currency (CBDC) for the Euro area, known as the "digital euro." The ECB has published a "Frequently Asked Questions" (FAQ) document and other materials to address public concerns regarding privacy, security, and utility. The authors identify a critical gap between the ECB's public assurances and the technical, legal, and economic realities of the proposed design. Specifically, the paper argues that the current design relies on unrealistic security assumptions (particularly regarding offline payments), creates unprecedented surveillance risks through centralized data aggregation, lacks clear liability frameworks, and offers no tangible societal benefits over existing payment systems or physical cash. The project risks being overly complex, economically burdensome, and technically flawed without clear advantages for users.

Methodology
The authors employ a critical analysis of the ECB's publicly available documentation, including the official FAQ, legislative proposals, technical reports, and tender documents. They systematically compare the ECB's claims against established cryptographic principles (e.g., Kerckhoffs' principle, the CAP theorem), historical records of hardware security breaches, and existing economic and legal frameworks. The analysis is structured around six key findings (KF1–KF6) derived from a detailed review of the digital euro's two-tiered architecture (online and offline versions). The authors also utilize comparative analysis with existing digital payment systems (e.g., credit cards, PayPal, Bitcoin, GNU Taler) and physical cash to highlight design shortcomings.

Key Contributions and Findings
The paper presents six primary key findings (KF) that challenge the viability and safety of the proposed digital euro:

• KF1: Privacy Erosion via Central Monitoring: The online version of the digital euro requires a central database at the ECB to track all account balances and transactions. While the ECB claims transactions are pseudonymized, the authors argue this allows for the reconstruction of "patterns of life" and detailed surveillance. Unlike current digital payments where data is siloed across thousands of institutions, the digital euro centralizes this data, creating a high-value target for cyberattacks and enabling mass surveillance that exceeds the privacy risks of contemporary systems.
• KF2: Impossibility of Secure Offline Anonymity: The offline version promises full anonymity and double-spending protection without internet connectivity. The authors argue this contradicts the CAP theorem (a distributed system cannot be simultaneously consistent, available, and partition-tolerant). The design relies on "secure hardware" (e.g., Secure Elements, eSIMs) to prevent double-spending by the device owner. However, historical evidence shows that consumer-grade hardware cannot withstand physical attacks indefinitely, especially when the potential reward (unlimited duplication of digital currency) outweighs the cost of attack. Consequently, offline payments cannot be both fully anonymous and secure against double-spending.
• KF3: Unclear Liability and Financial Risk: The design fails to specify liability in the event of offline fraud or double-spending. The ECB states that the PSP, merchant, or consumer might be liable, but never the ECB itself. Given the potential for unlimited digital euro creation if hardware is compromised, the financial exposure is unbounded and could threaten the stability of the currency. The lack of a clear compensation mechanism for victims of such fraud remains a critical legal gap.
• KF4: Lack of Economic Incentives and Market Distortion: The design imposes significant integration costs on merchants and Payment Service Providers (PSPs) without clear economic incentives. The fee structure and mandatory acceptance rules favor large existing players, potentially leading to market oligopolization. Furthermore, the "reverse waterfall" mechanism (automatic funding from linked bank accounts) introduces new security risks where a compromised digital euro account could drain linked commercial bank accounts.
• KF5: Absence of Tangible Societal Benefits: The online version largely duplicates existing digital payment infrastructure without offering superior privacy or utility. The offline version, while theoretically offering cash-like properties, is technically unfeasible to secure. The authors argue that the digital euro adds complexity without providing unique benefits, such as improved resilience to cyberattacks or technical disruptions, especially since offline usage still requires internet connectivity for initial funding and final settlement.
• KF6: Exclusionary Governance and Proprietary Design: The design process has been exclusionary, with key architectural decisions (online/offline separation, waterfall mechanism, secure hardware reliance) made prior to public consultation. The reliance on proprietary, non-European hardware and "security by obscurity" contradicts the principles of open standards and Free/Libre Open Source Software (FLOSS), which are essential for transparency, trust, and interoperability.

Results
The analysis concludes that the current digital euro design is fundamentally flawed.

• Privacy: The online version offers less privacy than existing systems due to centralization; the offline version's privacy guarantees are mathematically and practically unattainable without compromising security.
• Security: The offline version is vulnerable to double-spending due to the physical control users have over their devices, a vulnerability that cannot be fully mitigated by current hardware security technologies.
• Economics: The project imposes high costs on society (via taxes and merchant fees) while offering no clear advantage over existing solutions. It risks stifling innovation by favoring incumbent providers and creating a "black box" payment system.
• Governance: The process lacks transparency and inclusivity, with critical decisions locked in before meaningful public or expert input could alter the fundamental architecture.

Significance and Recommendations
The paper does not argue against the concept of a common digital payment system for the Euro area but asserts that the current proposal is unsuitable. The authors emphasize that unless clear, uncontroversial benefits are established, the introduction of the digital euro in its current form should be avoided.

The authors provide four specific recommendations for a successful CBDC:

1. Acknowledge the impracticability of the offline version: Focus on a single, privacy-preserving online system rather than pursuing an unrealistic offline design based on unbreakable hardware.
2. Provide a real advantage: The system must offer a unique selling point, such as cash-like payer anonymity for online transactions, rather than merely adding a layer to existing infrastructure.
3. Convince instead of enforce: Acceptance of the digital euro should be voluntary for merchants, removing the need for mandatory roll-out and associated costs.
4. Build on existing solutions and Free/Libre Software: The system should be based on open designs and FLOSS to ensure transparency, trust, and interoperability, moving away from proprietary technology and "security by obscurity."

The paper concludes that the digital euro, as currently proposed, risks being a costly, complex, and insecure project that fails to deliver on its promises of privacy, security, and utility.