Searchable encryption aims at making efficient a seemingly easy task: outsourcing the storage of a database to an untrusted server, while keeping search features. With the development of Cloud storage services, for both private individuals and businesses, efficiency of searchable encryption became crucial: inefficient constructions would not be deployed on a large scale because they would not be usable. The key problem with searchable encryption is that any construction achieving ‘perfect security’ induces a computational or a communicational overhead that is unacceptable for the providers or for the users — at least with current techniques and by today’s standards.
This thesis proposes and studies new security notions and new constructions of searchable encryption, aiming improving efficiency and security. In particular, we start by considering the forward and backward privacy of searchable encryption schemes, what it implies in terms of security and efficiency, and how we can realize them. Then, we show how to protect an encrypted database user against active attacks by the Cloud provider, and that such protections have an inherent efficiency cost. Finally, we take a look at existing attacks against searchable encryption, and explain how we might thwart them.
My work has been awarded the 2018 Ph.D. award by CNRS’ GDR Sécurité Informatique (information security research group).