Highly privacy-protecting data sharing in a tree structure

• We propose a way to store data in a non trusted cloud storage provider.
• We make use of the advanced cryptographic tool called “proxy re-encryption”.
• We provide a way for customers to share files and folder by modifying the standard proxy re-encryption paradigm.
• We show that a true implementation of such system is very efficient and can easily be embedded into commercial products.

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.