Secret extraction attacks against obfuscated IQP circuits

Kavli Affiliate: David Gross

| First 5 Authors: David Gross, Dominik Hangleiter, , ,

| Summary:

Quantum computing devices can now perform sampling tasks which, according to
complexity-theoretic and numerical evidence, are beyond the reach of classical
computers. This raises the question of how one can efficiently verify that a
quantum computer operating in this regime works as intended. In 2008, Shepherd
and Bremner proposed a protocol in which a verifier constructs a unitary from
the comparatively easy-to-implement family of so-called IQP circuits, and
challenges a prover to execute it on a quantum computer. The challenge problem
is designed to contain an obfuscated secret, which can be turned into a
statistical test that accepts samples from a correct quantum implementation. It
was conjectured that extracting the secret from the challenge problem is
NP-hard, so that the ability to pass the test constitutes strong evidence that
the prover possesses a quantum device and that it works as claimed.
Unfortunately, about a decade later, Kahanamoku-Meyer found an efficient
classical secret extraction attack. Bremner, Cheng, and Ji very recently
followed up by constructing a wide-ranging generalization of the original
protocol. Their IQP Stabilizer Scheme has been explicitly designed to
circumvent the known weakness. They also suggested that the original
construction can be made secure by adjusting the problem parameters. In this
work, we develop a number of secret extraction attacks which are effective
against both new approaches in a wide range of problem parameters. The
important problem of finding an efficient and reliable verification protocol
for sampling-based proofs of quantum supremacy thus remains open.

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