Microsoft Research

Cloud computing sparked interest in Verifiable Computation protocols, which allow a weak client to securely outsource com-putations to remote parties. Recent work has dramatically re-duced the client’s cost to verify the correctness of results, but the overhead to produce proofs largely remains impractical. Geppetto introduces complementary techniques for reducing prover overhead and increasing prover flexibility. With Multi-QAPs, Geppetto reduces the cost of sharing state between com-putations (e.g., for MapReduce) or within a single computa-tion by up to two orders of magnitude. Via a careful instantia-tion of cryptographic primitives, Geppetto also brings down the cost of verifying outsourced cryptographic computations (e.g., verifiably computing on signed data); together with Geppetto’s notion of bounded proof bootstrapping, Geppetto improves on prior bootstrapped systems by five orders of magnitude, albeit at some cost in universality. Geppetto also supports qualitatively new properties like verifying the correct execution of propri-etary (i.e., secret) algorithms. Finally, Geppetto’s use of energy-saving circuits brings the prover’s costs more in line with the program’s actual (rather than worst-case) execution time. Geppetto is implemented in a full-fledged, scalable compiler that consumes LLVM code generated from a variety of apps, as well as a large cryptographic library.