Paper 2023/583

Reusable, Instant and Private Payment Guarantees for Cryptocurrencies

Akash Madhusudan, KU Leuven, imec-COSIC
Mahdi Sedaghat, KU Leuven, imec-COSIC
Samarth Tiwari, Centrum Wiskunde & Informatica
Kelong Cong, KU Leuven, imec-COSIC
Bart Preneel, KU Leuven, imec-COSIC

Despite offering numerous advantages, public decentralized cryptocurrencies such as Bitcoin suffer from scalability issues such as high transaction latency and low throughput. The vast array of so-called Layer-2 solutions tackling the scalability problem focus on throughput, and consider latency as a secondary objective. However, in the context of retail payments, instant finality of transactions is arguably a more pressing concern, besides the overarching concern for privacy. In this paper, we provide an overlay network that allows privacy-friendly low latency payments in a retail market. Our approach follows that of a recent work called Snappy, which achieved low latency but exposed identities of customers and their transaction histories. Our construction ensures this data is kept private, while providing merchants with protection against double-spending attacks. Although our system is still based upon customers registering with a collateral, crucially this collateral is reusable over time. The technical novelty of our work comes from randomness-reusable threshold encryption (RRTE), a cryptographic primitive we designed specifically for the following features: our construction provably guarantees payments to merchants, preserves the secret identity of honest customers and prevents their transactions from being linked. We also present an implementation of our construction, showing its capacity for fast global payments in a retail setting with a delay of less than 1 second.

Available format(s)
Cryptographic protocols
Publication info
Published elsewhere. Australasian Conference on Information Security and Privacy 2023
Instant PaymentsPayment GuaranteesBlockchainCryptocurrencies
Contact author(s)
Akash madhusudan @ esat kuleuven be
ssedagha @ esat kuleuven be
Samarth tiwari @ cwi nl
kelong cong @ esat kuleuven be
bart preneel @ esat kuleuven be
2023-04-28: approved
2023-04-24: received
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Creative Commons Attribution


      author = {Akash Madhusudan and Mahdi Sedaghat and Samarth Tiwari and Kelong Cong and Bart Preneel},
      title = {Reusable, Instant and Private Payment Guarantees for Cryptocurrencies},
      howpublished = {Cryptology ePrint Archive, Paper 2023/583},
      year = {2023},
      note = {\url{}},
      url = {}
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