Paper 2026/1482 Original: eprint.iacr.org/2026/1482 ↗

Practical Adaptor Signatures: Security and Applications

Abstract

Adaptor signatures allow a signer to publish a pre‑signature that can be transformed into a valid signature by anyone once a secret witness is learned. Poelstra first suggested this primitive to bypass the limited scripting capabilities of Bitcoin. These schemes were later formalized by Aumayr et al. (ASIACRYPT 2021) and refined by Dai et al. (INDOCRYPT 2022) and Gerhart et al. (EUROCRYPT 2024). In this work, we revisit the constructions of adaptor signatures deployed in practice without any formal proof of security. First, we demonstrate that the current security model does not capture the ECDSA adaptor signature that underlies most real‑world systems. Second, we propose a relaxed definition and prove that it is satisfied by the ECDSA adaptor construction under the strong unforgeability of ECDSA. Finally, focusing on oracle‑based conditional payments, we formulate the first security model for adaptor‑based Discreet Log Contracts (DLCs) and show that our relaxed notion suffices for their security.