OblivShare: Towards Privacy-Preserving File Sharing with Oblivious Expiration Control

People have personal and/or business need to share private and confidential documents; however, often at the expense of privacy. Privacy aware users demand that their data is secure during the entire life cycle, and not residing in clouds indefinitely. A trending feature in industry is to set download constraints of shared files - a file can be downloaded for a restricted number of times and/or within a limited time framework. Metadata privacy becomes concerning with web services and applications providing such additional level of security control but not hiding the metadata. There is no prior research focusing on privacy-preserving expiration control, hence we propose OblivShare, a privacy-preserving file sharing scheme to proactively fill the gap. The scheme is based on ORAM for secure computation that 1) supports file expiration at users' control, 2) hides expiration metadata from the server, 3) server is fully oblivious of file access pattern and expiration state of a file. We demonstrate that our protocol has a complexity poly-logarithmic to the number of files while achieving privacy of metadata.