How does one prove a claim about a highly sensitive object such as a nuclear weapon without revealing information about the object? This paradox has challenged nuclear arms control for more than five decades. We present a mechanism in the form of an interactive proof system that can validate the structure and composition of an object, such as a nuclear warhead, to arbitrary precision without revealing either its structure or composition. We introduce a tomographic method that simultaneously resolves both the geometric and isotopic makeup of an object. We also introduce a method of protecting information using a provably secure cryptographic hash that does not rely on electronics or software. These techniques, when combined with a suitable protocol, constitute an interactive proof system that could reject hoax items and clear authentic warheads with excellent sensitivity in reasonably short measurement times.
How does one prove a claim about a highly sensitive object such as a nuclear weapon without revealing information about the object? This paradox has challenged nuclear arms control for more than five decades. We present a mechanism in the form of an interactive proof system that can validate the structure and composition of an object, such as a nuclear warhead, to arbitrary precision without revealing either its structure or composition. We introduce a tomographic method that simultaneously resolves both the geometric and isotopic makeup of an object. We also introduce a method of protecting information using a provably secure cryptographic hash that does not rely on electronics or software. These techniques, when combined with a suitable protocol, constitute an interactive proof system that could reject hoax items and clear authentic warheads with excellent sensitivity in reasonably short measurement times.
Future nuclear arms-control agreements may call for reductions of the total number of nuclear weapons and warheads in the world arsenals. Such agreements would require new trusted verification mechanisms to confirm that items presented to inspectors are nuclear warheads and not spoofs. Proliferation and national security concerns require, however, that inspectors gain no warhead design information through this process. To address this paradox, considerable efforts have been directed towards the development of "information barriers." These barriers consist of automated measurement systems that process sensitive information but only display the results of internal analysis in a binary valid/invalid manner. These systems are, by their nature, at risk of electronic tampering and snooping – and their trusted implementation has so far proved extremely difficult to realize. This thesis takes radically different directions to address this challenge. It demonstrates new approaches to information protection and trusted instruments for nuclear warhead verification that are based on the cryptographic concepts of zero-knowledge proofs and physically unclonable functions. To the author's knowledge, this thesis provides the first demonstration of a zero-knowledge physical measurement technique. Using fast neutron differential radiography and superheated emulsion detectors, such a technique can show two objects have identical geometry and opacity to 14-MeV neutrons without revealing what these properties are. This zero-knowledge feature no longer holds when the objects compared are significantly different. Such a technique could form the basis of a template-matching verification system that could confirm the authenticity of nuclear weapons without sharing any secret design information. The thesis then introduces and demonstrates key elements of an optical physical unclonable function sensitive to neutrons and based on superheated emulsions. Such sensors are unique objects that cannot be cloned or simulated. The data they produce are a function of both their internal disordered structure and the physical quantity they measure. Due to their sensitivity against any structural variation, including through neutron irradiation, it is possible to show that they – or the data they have recorded -- have not been tampered with. Such sensors could be used by adversarial parties in sensitive facilities without the risk of being compromised.
Nuclear disarmament treaties are not sufficient in and of themselves to neutralize the existential threat of the nuclear weapons. Technologies are necessary for verifying the authenticity of the nuclear warheads undergoing dismantlement before counting them toward a treaty partner's obligation. Here we present a concept that leverages isotope-specific nuclear resonance phenomena to authenticate a warhead's fissile components by comparing them to a previously authenticated template. All information is encrypted in the physical domain in a manner that amounts to a physical zero-knowledge proof system. Using Monte Carlo simulations, the system is shown to reveal no isotopic or geometric information about the weapon, while readily detecting hoaxing attempts. This nuclear technique can dramatically increase the reach and trustworthiness of future nuclear disarmament treaties.
Glaser, Barak, and Goldston recently described an approach for nuclear warhead verification based on the cryptographic concept of a zero-knowledge protocol (ZKP).The verification approach included both procedural elements and a physical implementation.A group of Sandia National Laboratories researchers, whose expertise include radiation instrumentation design and development, cryptography, and arms control verification implementation, jointly reviewed the paper and identified specific challenges to implementing the approach as well as some opportunities.This paper compares the ZKP concept as presented by Glaser et al., to other warhead verification concepts and approaches described in the literature.The paper also summarizes challenges and opportunities for elements of this (new) approach.We note that ZKP as used in cryptography is a useful model for the arms control verification problem, but find that the direct analogy to arms control breaks down quickly.For example, fault tolerance in cryptographic ZKP is achieved by brute force repetition of the challenge/response procedure; in arms control, repeated measurements can be expensive.The ZKP methodology fits within the general class of template-based verification techniques, where template in this case refers to a reference measurement that is used for comparison.Template methods in general confirm that a given object is like another object that has already been accepted as a warhead by some other means.This can be a powerful verification approach, but requires independent means to trust the authenticity of the reference warhead -a standard that may be difficult to achieve.Note that this use of template differs from that of Glaser et al., who use the term to describe the accepted reference warhead.In the ZKP approach as described, the reference warhead must be presentwith inspector confidence in its provenance-at each subsequent confirmation measurement.This imposes significant additional constraints on maintaining continuity of knowledge of the reference between inspections.Despite some technical challenges, the concept of last-minute selection of the pre-loads and equipment could be a valuable component of a verification regime.In addition, the neutron transmission image using a bubble detector array is an interesting idea that can be considered for template measurements independently of ZKP..
In this paper, we discuss the question how physical statements can be proven remotely over digital communication channels without using classical secret keys, and without assuming tamper-resistant and trusted measurement hardware in the location of the prover. Examples for the considered physical statements are: (i) “the temperature of a certain object is X◦C”, (ii) “two certain objects are positioned at distance X”, or (iii) “a certain object has been irreversibly altered or destroyed”. In lack of an established name, we would like to call the corresponding security protocols ”virtual proofs of reality” (VPs). While a host of variants seems conceivable, this paper focuses on VPs in which the verifier has handed over one or more specific physical objects Oi to the prover at some point prior to the VP. These “witness objects” assist the prover during the proof, but shall not contain classical digital keys nor be assumed tamper-resistant in the classical sense. The prover is allowed to open, inspect and alter these objects in our adversarial model, only being limited by current technology, while he shall still be unable to prove false claims to the verifier. In order to illustrate our concept, we give example protocols built on temperature sensitive integrated circuits, disordered optical scattering media, and quantum systems. These protocols prove the temperature, destruction/modification, or relative position of witness objects in the prover’s location. Full experimental realizations of these schemes are beyond the scope of this paper. But the protocols utilize established technologies from the areas of physical unclonable functions and quantum cryptography, and hence appear plausible also without such proof. Finally, we also discuss potential advancements of our method in theory, for example “public virtual proofs” that function without exchanging witness objects Oi between the verifier and the prover. Our work touches upon and partly extends several established cryptographic and security concepts, including physical unclonable functions, quantum cryptography, and interactive proof systems. Keywords-Virtual Proofs of Reality (VPs), Physical Unclonable Functions (PUFs), Interactive Proof Systems, Quantum Cryptography, Physical Cryptography
Position verification schemes are interactive protocols where entities prove their physical location to others; this enables interactive proofs for statements of the form "I am at a location L." Although secure position verification cannot be achieved with classical protocols (even with computational assumptions), they are feasible with quantum protocols.
In this paper we introduce the notion of zero-knowledge position verification, which generalizes position verification in two ways:
1. enabling entities to prove more sophisticated statements about their locations at different times (for example, "I was NOT near location L at noon yesterday").
2. maintaining privacy for any other detail about their true location besides the statement they are proving.
We construct zero-knowledge position verification from standard position verification and post-quantum one-way functions. The central tool in our construction is a primitive we call position commitments, which allow entities to privately commit to their physical position in a particular moment, which is then revealed at some later time.