THE FUTURE OF DIGITAL IDENTITY: PRIVACY-PRESERVING FRAMEWORKS USING ZERO-KNOWLEDGE BLOCKCHAIN ARCHITECTURE

Abstract

Digital identity underpins access to financial, health, government and commercial services, yet prevailing models force individuals to disclose far more personal data than any transaction requires and concentrate that data in repositories that are repeatedly breached. Self-sovereign identity on blockchains returns control to the individual but, when credentials or their hashes are published or presented in full, it creates new risks of correlation and over-disclosure. This paper proposes ZK-ID, a privacy-preserving digital identity framework built on zero-knowledge blockchain architecture. A holder converts an issuer-signed credential into a zero-knowledge proof that a statement about it is true, such as being over eighteen or belonging to a set of accredited users, without revealing the underlying attributes. The proof is stored on a blockchain, validated by a verification smart contract and made available to verifiers and third parties, while sensitive artefacts remain off-chain in content-addressed storage. The framework combines zk-SNARK circuits, Poseidon-based Merkle accumulators, nullifiers for replay protection and revocation, and a three-phase protocol that also supports privacy-preserving data trading among sellers and buyers. We formalise its security goals of completeness, soundness, zero knowledge and unlinkability, and a cost model for latency and gas. A prototype was evaluated for four circuits on desktop and smartphone clients and compared with a centralised identity provider and a hash-based self-sovereign baseline. The combined proof was generated in 1.12 s on a desktop and 3.4 s on a smartphone, has a size of 192 bytes and is verified on-chain for about 232,000 gas. Raw attributes disclosed per verification fell from eight to zero, and a linkability adversary achieved 50.4% accuracy, which is indistinguishable from guessing. None of 10,000 forged proofs was accepted. The results show that zero-knowledge blockchain architectures can deliver strong privacy with practical performance for the next generation of digital identity.