Malicious Party Accountability Based On ORAM In Cloud Environments

In cloud storage,data owners store data in third parties that are not under their absolute control,and data security and user privacy leakage become hidden problems.Even data are encrypted,the third party can deduce users privacy by collecting and analyzing user access pattern.To prevent users privacy leakage from access pattern analysis,there are many studies devoted to applying Oblivious Random Access Machine(ORAM)to cloud storage to regulate the data structure and access process,but properties of ORAM bring new challenges to cloud storage.The obliviousness property of ORAM makes user tampering with data easily,while the system is still confronted with the traditional cloud accountability problem that the cloud server is untrusted.It is necessary to provide an efficient data integrity protection and malicious parties accountability scheme.The existing work of ORAM accountability uses log to record users access paths,which is inefficient.Moreover,in the existing scheme,the cloud server has not to be held accountable.In the cloud multi-user scenario,this research adds access control in ORAM,and designs malicious parties accountability algorithm considering the two problems at the same time.Based on the related theories of malicious parties accountability in ORAM,this paper proposes a Traceable ORAM(T-ORAM).The scheme designs structures of bucket and block in the ORAM tree,and the access process to find corrupted data timely.For the problem that existing accountability work for ORAM is time and storage consuming,the scheme designs an accountability algorithm with high efficiency and low storage overhead based on group signatures.Furthermore,under a stronger threat model,this paper proposes a Blockchain-based Traceable ORAM(BT-ORAM).By utilizing the blockchain technology,BT-ORAM achieves a more comprehensive accountability algorithm for ORAM.Experiments show that T-ORAM has less storage overhead and higher accountability efficiency than the existing solutions.BT-ORAM has more comprehensive accountability of malicious parties and higher security than the existing ORAM-based accountability schemes while it has little impact on read and write performance.