SPECTRA: Selective Proof and Edge-Centric Traceability : A Privacy-Preserving Blockchain for Distributed and Confidential Verification

Blockchain technology ensures immutability and transparency but inherently exposes stored data to all network participants, making it unsuitable for domains requiring confidentiality. This paper presents a privacy-preserving traceability framework that redefines transparency as selective verifiability. The proposed architecture integrates a Hyperledger-based blockchain with Private Data Collections (PDCs) and a novel hash-verifiable binding mechanism linking each physical item to its digital certificate without revealing sensitive identifiers. A deterministic binding identifier (SHA-256 composite hash) connects the NFC tag, digital certificate, and production batch, enabling public verification of authenticity while keeping private data on-chain. A one-shot certification logic further prevents certificate reuse or cloning by transforming authenticity into a single-use cryptographic event. The system has been fully implemented and tested within the licorice supply chain of Southern Italy, demonstrating practical feasibility and extensibility to other sectors such as healthcare and luxury goods.