E-SC: Collusion-Resistant Secure Outsourcing of Sequence Comparison Algorithm

The sequence comparison of large-scale string-typed data is fundamental in computer science and other computational disciplines. Its development has been promoted into an emerging outsourcing service by the almost unlimited powerful computing and storage capabilities from public clouds. The privacy preservation and effective utility of the outsourced sensitive information are key requirements now facing this service. All of the secure two-party computation protocols in existing solutions, however, cannot be free from the assumption of non-colluding servers under multi-server models, and thus fail to defend against some attacks from cloud service providers. For this reason, we present encrypted sequence comparison (E-SC), the first security system that works by executing encrypted sequence comparison under a single-server model. Two character sequences are encrypted by end users before outsourcing, while the encrypted character sequences are compared directly by a single cloud server to return their similarity results. To accomplish this goal, novel computable encryption algorithms are designed in this paper. Then, a collusion-resistant outsourcing is achieved using non-interactive padding, partition, and expansion mechanisms. Results of simulation experiments demonstrate that the client-side overhead is quadratic in the input number of salt values, along with an optimal server-side performance. Also, the overall runtime of our E-SC system is positively correlated with its security level, which is more practical in realistic applications.