METHOD FOR FORMING AN INTER-REGISTRY INTERACTION PROTOCOL WITH MINIMAL PERSONAL DATA DISCLOSURE

Abstract

The article addresses the scientific and practical problem of excessive personal data disclosure during interactions between government electronic registries. In many cases, an administrative or legal decision requires only confirmation that a specified condition has been satisfied; nevertheless, the requesting system receives the value of the original attribute or a fragment of the registry record. This approach increases the amount of data available to the verifier, complicates control over its subsequent use, and creates additional risks of correlating information across different information systems. The aim of the study is to develop a method for constructing a policy-dependent inter-registry interaction protocol that verifies whether a request is permitted, confirms a specified predicate without disclosing the original attribute, and creates a verifiable audit record without storing personal data or persistent correlation data in a permissioned blockchain. The method combines a versioned minimum-disclosure profile; validation of the purpose, legal basis, audience, validity period, and predicate parameters; binding of the ZK proof to the context of a specific operation; and the generation of a keyed audit commitment. Only the minimum information required for subsequent integrity verification is recorded in the blockchain, whereas the complete evidentiary data are retained in a protected off-chain repository. The formal model is presented for a range predicate and supplemented with decision-acceptance conditions, replay protection, and policy freshness validation. Domain-specific conditions are checked before cryptographic operations are performed, preventing a cryptographically valid proof from being accepted for an unauthorised purpose. The study also defines the composition of on-chain and off-chain data, the procedure for recomputing the audit commitment, and scenarios for detecting proof modification, nonce reuse, outdated policy versions, and stale registry assertions. The reference prototype was implemented on the secp256k1 curve using Pedersen commitments, bit decomposition, non-interactive OR proofs, Ed25519, and HMAC-SHA-256. After 15 warm-up runs, 150 timing measurements and 2,000 functional tests across ten classes were conducted. The median proof generation time was 30.587 ms, while the median verification time was 34.663 ms; the corresponding 95th percentiles were 32.939 ms and 37.003 ms. The serialised proof size was 7,185 bytes. All valid requests were accepted, while violations involving the purpose, parameters, audience, validity period, policy version, status freshness, nonce uniqueness, and data integrity were detected. For the evaluated predicate, the original attribute was not transmitted to the verifier. The principal scientific contribution is the formalisation of an end-to-end relationship between an authorised purpose, a minimal predicate, a context-bound proof, and a private audit anchor. The proposed method can be used as a control layer between a policy service, a source registry, and a permissioned blockchain.