Security and privacy issues with centralized exchange services have motivated the design of atomic swap protocols for decentralized trading across currencies. These protocols follow a standard blueprint similar to the 2-phase commit in databases: (i) both users first lock their coins under a certain (cryptographic) condition and a timeout; (ii-a) the coins are swapped if the condition is fulfilled; or (ii-b) coins are released after the timeout. The quest for these protocols is to minimize the requirements from the scripting language supported by the swapped coins, thereby supporting a larger range of cryptocurrencies. The recently proposed universal atomic swap protocol [IEEE S&P’22] demonstrates how to swap coins whose scripting language only supports the verification of a digital signature on a transaction. However, the timeout functionality is cryptographically simulated with verifiable timelock puzzles, a computationally expensive primitive that hinders its use in battery-constrained devices such as mobile phones. In this state of affairs, we question whether the 2-phase commit paradigm is necessary for atomic swaps in the first place. In other words, is it possible to design a secure atomic swap protocol where the timeout is not used by (at least one of the two) users? In this work, we present LightSwap, the first secure atomic swap protocol that does not require the timeout functionality (not even in the form of a cryptographic puzzle) by one of the two users. LightSwap is thus better suited for scenarios where a user, running an instance of LightSwap on her mobile phone, wants to exchange coins with an online exchange service running an instance of LightSwap on a computer. We show how LightSwap can be used to swap Bitcoin and Monero, an interesting use case since Monero does not provide any scripting functionality support other than linkable ring signature verification.
Foundations and Tools for Client-Side Web Security Cryptographic Foundations for Future-proof Internet Security Forschungszentrum für Cybersicherheit und Datenschutz in Wien Blockchaintechnologien für das Internet der Dinge Vorbereitung für die Einreichung eines Kompetenzzentrums Comet K1 - Arbeitstitel Minerva
771527 P31621-N38 ViSP CDL-BOT 1360366
Europäischer Forschungsrat (ERC) Fonds zur Förderung der wissenschaftlichen Forschung (FWF) Wirtschaftsagentur Wien CDG Christian Doppler Forschungsgesellschaft Wirtschaftsagentur Wien
Madrid regional government as part of the program BLOQUES-CM SCUM Project (RTI2018-102043-B-I00) European Union NextGenerationEU/PRTR ONR Austrian Science Fund (FWF)