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Talks and Poster Presentations (with Proceedings-Entry):

E. Tairi, P. Moreno-Sanchez, M. Maffei:
"A2L: Anonymous Atomic Locks for Scalability in Payment Channel Hubs";
accepted as talk for: IEEE Symposium on Security and Privacy, Oakland, USA; 2021-05-23 - 2021-05-27; in: "42nd IEEE Symposium on Security and Privacy", (2021).



English abstract:
Payment channel hubs (PCHs) constitute a promising solution to the inherent scalability problems of blockchain technologies, allowing for off-chain payments between sender and receiver through an intermediary, called the tumbler. While state-of-the-art PCHs provide security and privacy guarantees against a malicious tumbler, they do so by relying on the scripting-based functionality available only at few cryptocurrencies, and they thus fall short of fundamental properties such as backwards compatibility and efficiency.

In this work, we present Trilero, the first PCH protocol to achieve all aforementioned properties. Trilero builds upon A2L, a novel cryptographic primitive that realizes a three-party protocol for conditional transactions, where the tumbler pays the receiver only if the latter solves a cryptographic challenge with the help of the sender, which implies the sender has paid the tumbler. We prove the security and privacy guarantees of A2L (which carry over to Trilero) in the Universal Composability framework and present a provably secure instantiation based on adaptor signatures. We implemented A2L and compared it to TumbleBit, the state-of-the-art Bitcoin-compatible PCH. Asymptotically, A2L has a communication complexity that is constant, as opposed to linear in the security parameter like in TumbleBit. In practice, A2L requires ∼33x less bandwidth than TumleBit, while retaining the computational cost (or providing 2x speedup with a preprocessing technique). This demonstrates that A2L (and thus Trilero) is ready to be deployed today.

In theory, we demonstrate for the first time that it is possible to design a secure and privacy-preserving PCH while requiring only digital signatures and timelock functionality from the underlying scripting language. In practice, this result makes Trilero backwards compatible with virtually all cryptocurrencies available today, even those offering a highly restricted form of scripting language such as Ripple or Stellar. The practical appealing of Trilero has resulted in a proof-of-concept implementation in the COMIT Network, a blockchain technology focused on cross-currency payments.

Keywords:
cryptography, blockchain, payment channel hub, adaptor signature, mixing, Bitcoin, security, privacy


Electronic version of the publication:
https://eprint.iacr.org/2019/589


Created from the Publication Database of the Vienna University of Technology.