Proof of Violation for Trust and Accountability of Cloud Database Systems

A cloud database is a system that typically runs on a cloud computing platform which is not maintained by the user but a service provider. The service provider can leak confidential data, modify the data, or return inconsistent data to users due to bugs, crashes, operator errors, or even malicious security attacks. Some cloud database systems provide Web interface or application programming interface for clients to access logs of database transactions. However, these logs are not cryptographic proofs. Clients cannot use these logs to prove whether a cloud service provider has violated some required properties such as data integrity, write serializability, and read freshness. A proof of violation (POV) scheme enables a client or a service provider to produce a precise proof of either the occurrence of the violation of properties or the innocence of the service provider. In this paper, we develop POV schemes for cloud database systems. First, we show that previously proposed cryptographic accountability protocols (CAPs), cannot be applied to cloud database systems directly. A CAP defines a multi-step handshaking protocol for clients and the service provider to exchange signed messages during service request and response so as to generate cryptographic proofs for later auditing. In addition, previously proposed auditing schemes are inappropriate to obtain the auditing requirements of SQL database according to collected cryptographic proofs. We design a new auditing scheme for cloud database systems. Implementation and experimental results are presented that demonstrate the feasibility of the proposed schemes. Service providers can use the proposed schemes to provide a mutual nonrepudiation guarantee for database transactions in their service-level agreements.