Implementation and Evaluation of Secure Outsourcing Scheme for Secret Sharing Scheme on Cloud Storage Services

In this paper, we discuss a scheme for storing user's data into cloud servers using secret sharing scheme (SSS), which is a scheme for giving the availability and information-theoretically secure confidentiality to the stored data. Generally, system models using SSS perform processing of SSS at client terminals of users. Then, the size of data sending from a client terminal is n times of that of original user's data, where n is a parameter of SSS and larger than one. We focus on the usage that mobile devices are used as client terminals. The properties of mobile devices have low computational power and poor communication bandwidth compared with desktop PC and notebook PC. In these devices, the size of the sending data should be reduced in order not to waste the communication bandwidth. Hence, we present a scheme to securely outsource the processing of SSS on an agent server, which achieves the size of data sending by user's client terminal (mobile device) is as same as original user's data. In addition, our scheme gives computationally secure confidentiality to the temporally user's data on agent server, and does not require additional key management for recovering original user's data by combining a SSS using exclusive-OR operations and stream cipher. Moreover, we implement a prototype system, and evaluate the processing time and security of the proposed scheme.