PicFS: The Privacy-Enhancing Image-Based Collaborative File System

Cloud computing makes available a vast amount of computation and storage resources in the pay-as-you-go manner. However, the users of cloud storage have to trust the providers to ensure the data privacy and confidentiality. In this paper, we present the Privacy-enhancing Image-based Collaborative File System (PicFS), a network file system that steganographically encodes itself into images and provides anonymous uploads and downloads from a media sharing website. PicFS provides plausible deniability by preventing traffic and image analysis by any third party from revealing the existence of PicFS or compromising its data. Because all accesses are anonymized, users of PicFS are dissociated from their data, which protects users against being compelled to release their keys. For further security and ease of use, we develop a method for automatically generating a large set of non-suspicious images to serve as input to the system. Our prototype leverages a number of existing technologies, including the F5 algorithm for steganography, Quick-Flickr for Flickr API access, Tor for anonymization, and FUSE-J for user-level file system calls. We show that the PicFS is indeed practical as the prototype demonstrates satisfactory performance in the real-world environment.