Trust No One: Thwarting "heartbleed" Attacks Using Privacy-Preserving Computation

A security bug in the OpenSSL library, codenamed Heartbleed, allowed attackers to read the contents of the corresponding server´s memory, effectively revealing passwords, master keys, and users´ session cookies. As long as the server memory contents are in the clear, it is a matter of time until the next bug/attack hands information over to attackers. In this paper, we investigate the applicability of privacy-preserving general-purpose computation, that would potentially render any information leaked indecipherable to attackers. Privacy is ensured by the use of homomorphically-encrypted memory contents. To this end, we explore the boundaries of general-purpose computation constrained for user data privacy. Specifically, we explore the minimum amount of information required for general purpose computation, which typically requires control flow and branches, and to what extent such information can be kept private from threats that have theoretically unlimited resources, including access to the internals of a target system.