Paper 2025/2170

Lattice-Based Linkable Ring Signatures for Anonymous and Accountable Whistleblowing

Abstract

Ring signatures allow an individual to sign a message on behalf of a group in such a way that the verifier can only confirm that someone in the group signed it, but cannot identify the actual signer. This strong anonymity, while desirable, may also be exploited for repeated or harmful activities. Linkable ring signatures mitigate this issue by enabling the system to recognise whether two signatures originate from the same signer, while still keeping the signer anonymous. Such constructions are essential in domains like e-voting, e-cash, privacy-preserving blockchain systems, and whistleblowing, where detecting repeated actions—such as double-spending or double-voting—is necessary to maintain system reliability. In this paper, we present a lattice-based linkable ring signature scheme designed to withstand quantum-era adversaries. The framework relies on exact and efficient zero-knowledge proofs, and employs a weak pseudorandom function (wPRF) to enable linkability. To demonstrate both ring membership and the generation of a unique tag, we integrate a Merkle tree accumulator, which also streamlines the verification steps. The scheme is instantiated using concrete parameter choices, allowing us to precisely evaluate how the signature size scales with different ring sizes. An important feature of our design is that it eliminates the need for trapdoor techniques, yet still produces a signature of roughly 0.22 MB when the ring contains 2^10 users. We further outline practical application scenarios, such as anonymous but accountable whistleblowing, to highlight the usefulness of the proposed construction.