The area of proof-based verified computation (outsourced computation built atop probabilistically checkable proofs and cryptographic machinery) has lately seen renewed interest. Although recent work has made great strides in reducing the overhead of naive applications of the theory, these schemes still cannot be considered practical. A core issue is that the work for the server is immense, in general; it is practical only for hand-compiled computations that can be expressed in special forms. This paper addresses that problem. Provided one is willing to batch verification, we develop a protocol that achieves the efficiency of the best manually constructed protocols in the literature yet applies to most computations. We show that Quadratic Arithmetic Programs, a new formalism for representing computations efficiently, can yield a particularly efficient PCP that integrates easily into the core protocols, resulting in a server whose work is roughly linear in the running time of the computation. We implement this protocol in the context of a system, called Zaatar, that includes a compiler and a GPU implementation. Zaatar is almost usable for real problems-without special-purpose tailoring. We argue that many (but not all) of the next research questions in verified computation are questions in secure systems.

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We consider interactive, proof-based verifiable computation: how can a client machine specify a computation to a server, receive an answer, and then engage the server in an interactive protocol that convinces the client that the answer is correct, with less work for the client than executing the computation in the first place? Complexity theory and cryptography offer solutions in principle, but if implemented naively, they are ludicrously expensive. Recently, however, several strands of work have refined this theory and implemented the resulting protocols in actual systems. This work is promising but suffers from one of two problems: either it relies on expensive cryptography, or else it applies to a restricted class of computations. Worse, it is not always clear which protocol will perform better for a given problem. We describe a system that (a) extends optimized refinements of the non-cryptographic protocols to a much broader class of computations, (b) uses static analysis to fail over to the cryptographic ones when the non-cryptographic ones would be more expensive, and (c) incorporates this core into a built system that includes a compiler for a high-level language, a distributed server, and GPU acceleration. Experimental results indicate that our system performs better and applies more widely than the best in the literature.

When a client outsources a job to a third party (e.g., the cloud), how can the client check the result, without reexecuting the computation? Recent work in proof-based verifiable computation has made significant progress on this problem by incorporating deep results from complexity theory and cryptography into built systems. However, these systems work within a stateless model: they exclude computations that interact with RAM or a disk, or for which the client does not have the full input.This paper describes Pantry, a built system that overcomes these limitations. Pantry composes proofbased verifiable computation with untrusted storage: the client expresses its computation in terms of digests that attest to state, and verifiably outsources that computation. Using Pantry, we extend verifiability to MapReduce jobs, simple database queries, and interactions with private state. Thus, Pantry takes another step toward practical proof-based verifiable computation for realistic applications.

We describe a new networking primitive, called a Path Verification Mechanism (PVM). There has been much recent work about how senders and receivers express policies about the paths that their packets take. For instance, a company might want fine-grained control over which providers carry which traffic between its branch offices, or a receiver may want traffic sent to it to travel through an intrusion detection service.While the ability to express policies has been well-studied, the ability to enforce policies has not. The core challenge is: if we assume an adversarial, decentralized, and high-speed environment, then when a packet arrives at a node, how can the node be sure that the packet followed an approved path? Our solution, ICING, incorporates an optimized cryptographic construction that is compact, and requires negligible configuration state and no PKI. We demonstrate ICING's plausibility with a NetFPGA hardware implementation. At 93% more costly than an IP router on the same platform, its cost is significant but affordable. Indeed, our evaluation suggests that ICING can scale to backbone speeds.