Paper 2026/294

Post-Quantum Adaptor Signatures with Strong Security from Cryptographic Group Actions

Abstract

We present One Round "Cheating" Adaptor Signatures (OR- CAS): a novel and efficient construction of adaptor signature schemes from CSI-FiSh. Our protocol improves substantially on existing group action-based schemes: Unlike IAS (Tairi et al., FC 2021), our scheme does not require expensive non-interactive zero-knowledge proofs, and unlike adaptor MCSI-FiSh (Jana et al., CANS 2024) our construction does not require any modification to the underlying digital signature scheme. We prove the protocol’s security under the strong security no- tions of Dai et al. (Indocrypt 2022) and Gerhart et al. (Eurocrypt 2024).

Note: This work began at the VT-Swiss Coding Theory and Cryptography Summer School and Collaboration Workshop in 2024. The fourth author is funded in part by the Commonwealth of Virginia’s Commonwealth Cyber Initiative (CCI), an investment in the advancement of cyber R&D, innovation, and workforce development. For more information about CCI, visit www.cyberinitiative.org. The fifth author is supported by the Italian PRIN2022 grant 2022J4HRR Mathematical Primitives for Post Quantum Digital Signatures. The sixth author is supported by armasuisse Science and Technology.