Paper 2025/1138

ZK-NR: A Layered Cryptographic Architecture for Explainable Non-Repudiation

Abstract

This paper introduces ZK-NR, a modular cryptographic protocol designed to ensure privacy-preserving non-repudiation in the co-production of digital public services. By integrating Merkle commitments, zero-knowledge proofs (STARKs), threshold BLS signatures, and post-quantum Dilithium authentication, ZK-NR enables the creation of secure, verifiable, and auditable evidence across decentralized infrastructures. Unlike traditional digital signatures or blockchain-based logs, ZK-NR provides formally verifiable attestations without disclosing sensitive content, making it suitable for public finance, e-government, and regulated digital ecosystems. The protocol is modeled in Tamarin and implemented as a proof-of-concept using open cryptographic tools. This contribution offers a reproducible foundation for future infrastructures requiring long-term trust, data minimization, and legal admissibility, particularly in contexts where citizens and institutions share responsibility for digital evidence. ZK-NR addresses the tension between confidentiality and accountability, providing an interoperable and future-ready layer for trustworthy public service delivery. This preliminary work focuses on architectural composition and implementation feasibility. It does not include formal security proofs.

Note: This report introduces the ZK-NR protocol as a layered cryptographic architecture for explainable non-repudiation. It includes practical artefacts for role-based signing, Merkle commitment, and STARK proof generation. The supplementary file zk-nr_sup_mat.zip contains all implementation scripts, logs, and instructions required to replicate the setup described in Section 4 and Appendix A. Note: This manuscript precedes a series of more formal documents currently under preparation, including UC-composable security proofs and symbolic verification with Tamarin. Those will be made available in separate submissions.