Place : LIX Salle Henri Poincaré
Abstract : Secure Multi-Party Computation (MPC) allows a set of “n” distrusting parties to compute functions on their private inputs while guaranteeing secrecy of inputs while ensuring correctness of the computation. Most MPC protocols can achieve such security only against a minority of corrupted parties (e.g., there is an honest majority > n/2). Based on cryptographic assumptions, security against dishonest majorities can be obtained but requires more computation and communication. These levels of security are often not sufficient in real life especially threats that require long-term security against powerful persistant attackers (e.g., so called Advanced Persistent Threats). In such cases, all the parties involved in the protocol may become corrupted at some point. Proactive MPC (PMPC)aims to address such mobile persistent threats; PMPC guarantees privacy and correctness against an adversary allowed to change the set of corrupted parties over time but that is bounded by a threshold at any given instant. Until recently, PMPC protocols existed only against a dishonest minority. The first generic PMPC protocol against a dishonest majority was introduced in a recent work to be presented in September 2018, it presents a feasibility result demonstrating that it can be achieved but with high communication complexity: O(n^4).