Bootstrap-based proxy reencryption for private multi-user computing

The increasingly popular paradigm of Cloud computing brings about many benefits both for clients and providers, but it also introduces privacy risks associated to outsourcing data and processes to an untrustworthy environment. In particular, the multi-user computing scenario is especially difficult to tackle from a privacy-preserving point of view, seeking to protect data from different users while allowing for flexible Cloud applications. This work leverages Gentry´s cryptographic bootstrapping operation as a means to endow fully homomorphic cryptosystem with proxy reencryption functionalities, targeted at the private multi-user and multi-key computing scenario. We provide an example implementation based on Gentry-Halevi cryptosystem, and a secure protocol that employs this primitive for solving the private multi-user computing scenario with non-colluding parties.