Securing multiparty protocols against the exposure of data to honest parties

Abstract

We consider a new adversarial goal in multiparty protocols, where the adversary may corrupt some parties. The goal is to manipulate the view of some honest party in a way, that this honest party learns the private data of some other honest party. The adversary itself might not learn this data at all. This goal, and such attacks are significant because they create a liability to the first honest party to clean its systems from second honest party’s data; a task that may be highly non-trivial. Cleaning the systems is essential to prevent possible security leaks in future. Protecting against this goal essentially means achieving security against several non-cooperating adversaries, where only one adversary is active, representing the real attacker, and each other adversary is passive, corrupting only a single party. We formalize the adversarial goal by proposing an alternative notion of universal composability. We show how existing, conventionally secure multiparty protocols can be transformed to make them secure against the novel adversarial goal.