Distributed auditing protocol for blockchain-based transactions using a distributed signature

Data privacy is a developing issue in the cyberspace. Users who send something through a public network want their data to be kept confidential. Service providers, in like manner, need to store valid data and avoid storing invalid data. Auditing protocols provide data validity and prevent the storing of invalid data. However, some problems including cooperation with a malicious auditor to register invalid data, deleting registered data, obtaining private data by service providers, and attacks to the network's point of failure still exists. This paper presents a blockchain-based protocol to audit transactions transferred on a blockchain called the DA-DS protocol. The blockchain is applied in the DA-DS protocol to provide immutability for stored data and distribute the network's point of failure. A distributed signature based on the ElGamal cryptosystem is applied in this paper for auditors and the ElGamal-based encryption algorithm to provide transaction confidentiality since the ElGamal cryptosystem does not provide key escrow. Therefore, users join the network have a security against privileged insider adversaries. In the DA-DS protocol, each confidential transaction is audited, off-chain, by all auditors. The audited transaction is then sent to the central authority for verification, and the central authority submits the audited transaction on the blockchain if the verification process is done successfully. Finally, in this paper, a security analysis of the DA-DS protocol is provided in the random oracle (RO) model. Subsequently, the performance was compared with other recently proposed auditing protocols, the result of which has shown that it higher efficiency.