Spatial Isolation Implies Zero Knowledge Even in a Quantum World

Zero knowledge plays a central role in cryptography and complexity. The seminal work of Ben-Or et al. (STOC 1988) shows that zero knowledge can be achieved unconditionally for any language in NEXP, as long as one is willing to make a suitable physical assumption: if the provers are spatially isolated, then they can be assumed to be playing independent strategies. Quantum mechanics, however, tells us that this assumption is unrealistic, because spatially-isolated provers could share a quantum entangled state and realize a non-local correlated strategy. The MIP* model captures this setting. In this work we study the following question: does spatial isolation still suffice to unconditionally achieve zero knowledge even in the presence of quantum entanglement? We answer this question in the affirmative: we prove that every language in NEXP has a 2-prover zero knowledge interactive proof that is sound against entangled provers; that is, NEXP ⊆ ZK-MIP*. Our proof consists of constructing a zero knowledge interactive PCP with a strong algebraic structure, and then lifting it to the MIP* model. This lifting relies on a new framework that builds on recent advances in low-degree testing against entangled strategies, and clearly separates classical and quantum tools. Our main technical contribution is the development of new algebraic techniques for obtaining unconditional zero knowledge; this includes a zero knowledge variant of the celebrated sumcheck protocol, a key building block in many probabilistic proof systems. A core component of our sumcheck protocol is a new algebraic commitment scheme, whose analysis relies on algebraic complexity theory.

Authors

• Alessandro Chiesa
• Michael A. Forbes 0001
• Tom Gur
• Nicholas Spooner

Keywords

• Protocols
• Quantum entanglement
• Complexity theory
• Probabilistic logic
• Quantum computing
• Cryptography
• Games
• Spatial Isolation
• Quantum World
• Zero Knowledge
• Entangled State
• Algebraic Structure
• Probabilistic System
• High Probability
• Black Box
• Proof Of Theorem
• Quantum Information
• Classical Components
• Probability 1
• Finite Field
• Part Of The Proof
• Total Degree
• Classical Protocol
• Boolean Function
• Single Query
• Unique Extension
• Zero-knowledge Proof
• zero knowledge, multi prover interactive proofs, quantum entangled strategies, interactive PCPs, sumcheck protocol, algebraic complexity