Towards secure and reliable cloud storage against data re-outsourcing

• We propose a scheme to prevent CSPs from re-outsourcing their clients’ data.
• We explore the economic server collusion problem among cloud storage services.
• Our scheme is efficient where a client does not need to download all its data.

To increase the profit, a semi-trusted cloud service provider may outsource the files of its client to some low expensive cloud service providers, which may violate the wishes of cloud users and impair their legitimate rights and interests. In this paper, a probabilistic challenge–response scheme is proposed to prove that users’ files are available and stored in a specified cloud server. In our scheme, common cloud infrastructure with some reasonable limits, such as rational economic security model, semi-collusion security model and response time bound, are exploited to resist the collusion of cloud servers. These limits guarantee that a malicious cloud service provider could not conduct a tt-round communication in a limited time. The security and performance analysis demonstrate that our scheme provides strong incentives against an economically rational cloud service provider from re-outsourcing its clients’ data to some other cloud providers.