Blockchain-Based Employment Contract System Architecture Allowing Encrypted Keyword Searches

Abstract

We introduce a blockchain-based online employment contract system to protect the rights and interests of both employees and employers. In the proposed model, an employer and a worker can interactively create a new electronic online contract, and the mutually signed contract is saved on a contract blockchain so that the contract becomes certifiable but cannot be forged by the contract signers. In particular, the blockchain in our system provides transactional privacy to protect sensitive personal information such as social identifier, contact information, income, and so forth, contained in the contract. Since a remote cloud server must provide not only secure storage, accessibility, and availability of all signed contracts, but also increased security in the server, we propose a new encrypted keyword search mechanism with enhanced search accuracy. Each contract is associated with encrypted keywords generated from the names of contractual parties and must remain confidential and anonymous even to the server. Although, the contracts must always be accessible by the contract signers, only the cloud server should be able to retrieve each user’s contract without decrypting the contract or identifying the contract signer. To meet these requirements, we propose a new encrypted keyword search mechanism based on Gentry’s homomorphic encryption technology; the server can find each user’s contract when two encrypted arbitrary keywords are homomorphic to each other. Since the keywords in the proposed system are based on person names or business names, they are easily predictable, and, thereby, many synonyms for a keyword can exist. Therefore, the proposed encrypted keyword search takes into account not only the keywords but also the ownership of each contract; in this way, the proposed search scheme is secure against a keyword guessing attack and provides strong search accuracy against the keyword synonyms. As a result, users can only access their own contracts, and the cloud server can exactly retrieve the requester’s contracts. Implementations for the proposed system and corresponding analysis on its security and simulated performance are provided.