LTRAS: A Linkable Threshold Ring Adaptor Signature Scheme for Efficient and Private Cross-Chain Transactions
Yi Liang, Jinguang Han
TL;DR
LTRAS addresses privacy, fairness, and efficiency in adaptor-signature-based cross-chain transactions by marrying conditional adaptability with a $(t,\\,n)$-threshold ring and linkability. The construction leverages a hard relation and a sliding window transformation to hide the signer’s accounts while enabling joint payments and preventing double-spending, with formal definitions and security proofs underpinning correctness, adaptability, witness extractability, and aEUF-CMA unforgeability under standard assumptions. The paper provides a concrete scheme, analyzes performance against existing baselines, and demonstrates practical applicability to cross-chain atomic swaps, notably between Bitcoin and Monero, with significant improvements in computation and communication for large rings. Overall, LTRAS offers a private, scalable, and atomic framework for multi-account blockchain operations that can extend to post-quantum settings in future work.
Abstract
Despite the advantages of decentralization and immutability, blockchain technology faces significant scalability and throughput limitations, which has prompted the exploration of off-chain solutions like payment channels. Adaptor signatures have been considered a promising primitive for constructing such channels due to their support for atomicity, offering an alternative to traditional hash-timelock contracts. However, standard adaptor signatures may reveal signer identity, raising potential privacy concerns. While ring signatures can mitigate this issue by providing anonymity, they often introduce high communication overhead, particularly in multi-account payment settings commonly used in UTXO-based blockchains like Monero. To address these limitations, we propose a Linkable Threshold Ring Adaptor Signature (LTRAS) scheme, which integrates the conditional binding of adaptor signatures, the multi-account payment of threshold ring signatures, and the linkability for preventing double-spending. The formal definition, security model and concrete construction of LTRAS are provided. We also analyze its security and evaluate its performance through theoretical analysis and experimental implementation. Experimental results demonstrate that our scheme achieve significantly lower computation and communication overhead compared to existing schemes in large ring sizes and multi-account payment scenarios. Finally, we discuss its application in cross-chain atomic swaps, demonstrating its potential for enhancing privacy and efficiency in blockchain transactions.