Highly Privacy-Protecting Data Sharing in a Tree Structure
S. Canard and J. Devigne

In this paper, we investigate the way to efficiently implement a highly privacy-protecting data sharing system in a cloud storage context. We suppose that several customers want to share some sensitive and personal data that are stored on a non-trusted cloud storage system, in such a way that the latter has no way to obtain the data in clear. For this purpose, we make use of an advanced cryptographic tool called a ``proxy re-encryption'' scheme. In this context, our contribution is twofold. We first modify existing proxy re-encryption schemes in such a way that customers can now manage dynamically a tree structure for their shared document, which was not possible with existing systems. We then present the first true implementation of such system where each client makes use of a smartphone to upload, download and share his/her documents. This way, we show that such system is really practical for a real-life use.