Universal and Trustless Large-Value Payments in Cryptocurrencies

Cryptocurrencies possess a natural advantage in financial applications where response time is not critical, given the well-known high latency and low throughput of blockchain technology. However, a notable gap exists in cryptocurrencies, specifically the absence of applications intentionally introducing delays in committing transactions to facilitate potential revocation operations. Large-Value Payment (LVP), a vital component in financial services, addresses this gap by enabling users to perform such operations. In this context, the payer retains the ability to revoke any number of payments within a pre-agreed timeframe T, while the payee gains the unrevoked transactions after T. In the blockchain landscape, trusted third-party platforms play a role analogous to traditional banking institutions, which can trivially realize LVPs. However, their centralized structure poses challenges such as a single point of failure, privacy concerns, and high transaction fees. Motivated by these limitations, we propose trustless large-value payment protocols with key characteristics: (i) trustlessness, eliminating reliance on any trusted party; (ii) revocability, allowing the payer to revoke payments within the predefined time; and (iii) universality, compatible with all current cryptocurrencies. In this paper, we formally define the semantic and security model of LVP, which paves the way for a new research direction. Building on this foundation, we present a straightforward yet efficient construction of LVP based on Bitcoin scripts. To overcome script-dependency limitations, we introduce a scriptless LVP protocol based on verifiable timed signatures and adaptor signatures. This achieves universality across different cryptocurrencies. We prove the security of our proposals in the Universal Composability framework and further enhance performance for multiple LVPs across diverse cryptocurrencies. Specifically, we design a protocol for secure witness reuse and employ verifiable timed discrete logarithm for revocability. Rigorous security analysis and performance evaluation confirm that both scripted and scriptless LVP protocols meet essential security objectives, providing practical solutions for users requiring transaction revocation without relying on trusted parties.