# A Cloud Microservices Architecture for Data Integrity Verifiability Based on Blockchain
###### Abstract  
The current digital age, mainly characterized by an economy based upon information technology, demands a data integrity service, even more so because organizations and companies are migrating their services over the cloud. This is not a simple task; it is cumbersome since traditional schemes in databases could be subject to modifications. However, it can be solved using blockchain technology. This paper provides a data integrity verifiability architecture for cloud systems based on blockchain. The architecture provides a mechanism to store events (as logs) within a blockchain platform from any cloud system. Users can then consult data integrity through a microservice, acting as an intermediate server that carries out a set of verification steps within the blockchain, which confirms the integrity of a previously stored log. Our architecture takes advantage of the blockchain strength concerning integrity, providing a traceability track of the stored logs. A prototype system and a case study were implemented based on the proposed architecture. Our experimental results show that the proposed decentralized architecture can be adapted to cloud existing systems that were born without blockchain technology and require a modular and scalable audit characteristic. blockchain; integrity; audit; microservices; cloud systems +
Footnote †: journal:  
information security properties. Thus, TCP/IP-based solutions layered on the internet have raised significant trust and privacy concerns. Blockchain seems to be a suited technology for dealing with cloud system data integrity, because blockchain is characterized by features, such as transparency, traceability, and security [12]. These features make the adoption of blockchain attractive toward enhancing information security, privacy, and trustworthiness in very different contexts. Firstly, this technology was developed to improve integrity in the Bitcoin network [13]; then, it gave way to other cryptocurrencies. Recently, blockchain and the smart contract extension have permitted considering other use cases, such as the supply chain, Internet of Things, healthcare systems, digital right management, insurance, financial systems, and real estate systems [14]. These implementations share a very important characteristic related to trust--a crucial element of blockchain technology [15; 16]. Blockchain applies cryptography and hash functions to chain the blocks, along with a decentralized structure, making it very difficult for third parties to manipulate the information compared to traditional databases. Its potential is enormous in information transactions, such as cloud storage. Blockchain technology itself already has the strengths of including logging and traceability mechanisms. However, the reality is that most organizations were born without it, and their storage information is executed via traditional databases (off-chain). A complete migration could imply very high economic costs since systems with high information content would require too much computational costs deploying their transactions on the blockchain network [17]. In this article, blockchain technology is used as a repository to store all events that can arise in an external system, ensuring its integrity. We provide an audit mechanism, propose a hybrid solution architecture on a permissionless blockchain with smart contract support. Each event, before being stored, is transformed in a log containing the attribute tags that respond to the following questions: how was the event generated? Who generated it? What included the event? Where was it generated? When was the event generated? The log is stored in the blockchain by executing smart contracts. This will allow validating and knowing the traceability of any data modification, guaranteeing if the information provides integrity or not, i.e., knowing the possible alterations by third parties.