Reducing Trust When Trust Is Essential

Trust is unavoidable in many complex systems. As users demand more functionality and convenient access, there is often a point at which a systems designer has no choice but to ask clients to place some level of trust in one participant in the system, be it a key management server or even just the integrity of some external hardware. This is in contrast to many cryptographic functionalities that will either perform as expected, or at least remain secure, without a client having to trust anything but their own integrity. The main focus of this thesis is to conduct a thorough analysis of two settings in which trust is essential and find new dimensions in which to reduce the amount of trust the participants are asked to put in the system for it to function as expected. First, we analyze remote storage where a third party is trusted to store and do access control on a client's data. Second, we study what additional assumptions are necessary in order to circumvent impossibility of fully secure MPC without an honest majority.

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