(2026-02) Post-Quantum Adaptor Signatures with Strong Security from Cryptographic Group Actions
2026-02-17
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).