Paper 2026/1394

Adaptor Signatures Meet BLS: Enabling Efficient Blockchain Applications with Unique Adaptor Signatures

Abstract

Blockchain-based cryptocurrencies give rise to a plenitude of advanced applications (such as cross-currency transfers or privacy-preserving payments) through blockchain protocols - cryptographic protocols that orchestrate the processing of financial transactions on the blockchain. To enable a modular design and to enhance reusability across different cryptocurrencies, many blockchain protocols are built upon adaptor signatures (AS), a well-studied cryptographic building block, which is natively supported by most digital signature schemes used for authorizing cryptocurrency transactions. An inherent limitation of AS-based blockchain protocols is the known impossibility to realize AS for unique signature schemes, such as BLS signatures. As a consequence, existing AS-based protocols cannot be executed on cryptocurrencies that base transaction authorization on BLS signatures (such as the Chia Network). For such cryptocurrencies, instead, new custom blockchain protocols need to be created, as recently done for the case of coin mixing (S&P'24) or atomic swaps between two cryptocurrencies with BLS-based transaction authorization (ESORICS'24). To avoid such complex and error-prone redesigns, in this work, we develop a novel notion of AS called Two-Party Asymmetric-Input Solitary-Output Adaptor Signature (2P-AISO-AS) that sidesteps the known impossibility result and that can be realized from both randomized (i.e., plain) and unique signature schemes. We provide efficient instantiations of 2P-AISO-AS from BLS and show that we can obtain performant, BLS-compatible blockchain protocols by replacing AS with 2P-AISO-AS in known AS-based protocols, including zero-knowledge contingent payments, atomic swaps, and coin mixing.