Paper 2026/1731 Original: eprint.iacr.org/2026/1731 ↗

Generic Ring-Signature Transforms for Fiat-Shamir with Aborts and Hash-and-Sign with Retry

Abstract

Ring signatures provide signer anonymity for ad hoc sets of public keys. Generic Abe-Ohkubo-Suzuki (AOS) transforms are well understood for plain Fiat--Shamir and hash-and-sign signatures, but not for their rejection-sampling variants: Fiat--Shamir with aborts (FSwA) and hash-and-sign with retry (HSwR). We formalize AOS ring transforms for FSwA and HSwR and analyze their security in the quantum random-oracle model. For unforgeability, we reduce security under adaptive ring-signing queries to security without signing queries using essentially the same assumptions as in security proofs for the corresponding ordinary signatures; handling adaptive corruption additionally requires the simulation property to remain valid after key exposure. Strong unforgeability additionally requires response uniqueness and special soundness for FSwA, or second-preimage resistance and non-invertibility for HSwR. The residual no-signing-query requirement admits generic reductions, but with loss exponential in the number of honest keys. Finally, an ML-DSA case study shows that augmented public keys achieve the required key-exposure simulation while identifying its limitations; we also identify conditions for candidate HSwR instantiations.