Automatic Teller Machines for Offline E-cash

2026-04-11

AI Summary

This work proposes a multi-issuer electronic cash system supporting offline withdrawals, addressing the limitation of traditional e-cash schemes that rely on centralized banks and fail during network outages. Building upon Camenisch et al.’s compact e-cash protocol, the system introduces a one-time transfer mechanism employing doubly anonymous cryptographic credentials. This design ensures unforgeability, unlinkability, and strong user privacy without requiring real-time connectivity to the issuing bank. By enabling secure credential issuance and verification in disconnected environments, the architecture significantly enhances system availability while preserving security guarantees. The proposed approach thus offers a practical solution for deploying electronic cash in low-connectivity or fully offline settings.

Technology Category

• Multiagent Systems: Mechanism Design
• Cognitive Modeling & Cognitive Systems: Social Cognition And Interaction
• Game Theory and Economic Paradigms: Mechanism Design

Application Category

• Security and Privacy: Cryptocurrency and smart contracts
• Economics, Online Markets and Human Computation: Economic aspects of blockchain and cryptocurrencies
• User Modeling, Personalization and Recommendation: User privacy protection in personalized systems

Abstract

Electronic cash (e-cash) is a digital alternative to physical currency that allows anonymous transactions between users and merchants. Typically, coins in an e-cash scheme are only dispensed through a central bank. A drawback of this approach is that the bank is always on the critical path during withdrawals, and if a reliable connection to the bank is temporarily unavailable, users may be unable to withdraw coins in a timely fashion. As with physical currency, there are benefits to supporting a decentralized infrastructure where withdrawals can be performed without involving the bank in the critical path. We propose the design of a new cryptographic bearer token that can be dispensed by automatic teller machines (ATM) in a fully offline e-cash scheme. Such bearer tokens provide anonymity, unforgeability and untraceability, i.e., users cannot be tracked by their spending activities or the locations of withdrawal. We formalize the requirements of an e-cash scheme with multiple issuers and propose an efficient design building on top of the compact e-cash protocol of Camenisch et al. (EUROCRYPT 2005). Our construction leverages an unforgeable and doubly-anonymous voucher that allows a one-time transfer of coins between an ATM and a user, while hiding their identities from parties not involved in the transaction.

Problem

• offline e-cash
• decentralized withdrawal
• automatic teller machines
• anonymous transactions
• bearer tokens

Innovation

• offline e-cash
• bearer token
• decentralized withdrawal
• double anonymity
• unforgeable voucher