Integrity and Consistency for Untrusted Services

A group of mutually trusting clients outsources an arbitrary computation service to a remote provider, which they do not fully trust and that may be subject to attacks. The clients do not communicate with each other and would like to verify the integrity of the stored data, the correctness of the remote computation process, and the consistency of the provider’s responses. We present a novel protocol that guarantees atomic operations to all clients when the provider is correct and fork-linearizable semantics when it is faulty; this means that all clients which observe each other’s operations are consistent, in the sense that their own operations, plus those operations whose effects they see, have occurred atomically in same sequence. This protocol generalizes previous approaches that provided such guarantees only for outsourced storage services.