Zero-Knowledge Nuclear Warhead Verification

Launched in 2011 with seed-funding from Global Zero and The Simons Foundation, our team has been pioneering a warhead verification approach based on the cryptographic concept of zero-knowledge proofs. The original concept was published in a Nature article in June 2014. Since then, we have been working on the development of a zero-knowledge object-comparison system and the procedures for its use in nuclear warhead inspections. The demonstration of such a system has been recently outlined in a Nature Communications article published in September 2016 (see video from the Princeton Plasma Physics Laboratory). This page summarizes briefly the main challenges of nuclear disarmament verification and outlines the concept of zero-knowledge warhead verification.

The Challenges of Nuclear Disarmament Verification

Existing nuclear arms-control agreements between the United States and Russia place limits on the number of deployed strategic nuclear weapons. Verification of these agreements takes advantage of the fact that deployed weapons are associated with unique and easily accountable delivery platforms, that is, missile silos, submarines and strategic bombers, to which agreed numbers of warheads are attributed. The next round of nuclear arms-control agreements, however, may place limits on the total number of nuclear weapons and warheads in the arsenals. This is a qualitatively new challenge because the design of nuclear weapons is highly classified information that cannot be exposed to international inspectors. A viable verification approach therefore has to resolve the tension between reliably verifying that the inspected warhead is authentic while avoiding disclosure of information about its design.

How many nuclear weapons are in today’s arsenals? There are roughly 16,000 nuclear warheads owned by 9 states. Among these, only about 20% (~3,000 warheads) are covered under international agreements (The New Start bilateral treaty between the U.S. and Russia). : Alex Glaser.

What Are Physical Zero-Knowledge Proofs?

Zero-knowledge proofs are mathematical cryptographic methods to demonstrate the validity of a claim while providing no further information beyond the claim itself. Originally developed for computational applications, we translated this mathematical concept and build a physical system that manifests the same fundamental properties. Our zero-knowledge object-comparison system can show that some objects are identical (in geometry and composition) without revealing what these objects are. Such a technique could form the basis of a verification system that could confirm the authenticity of nuclear weapons without sharing any secret design information.

How can we compare objects without learning what they are?
(a) We expose objects to a neutron beam and record their transmission and emission radiographs on detectors preloaded with the complement radiograph of a reference item (similar to a “negative”). If the item is valid (identical to the reference), the final radiograph is identical to the expected exposure if no object had been present. If the item is a spoof with an experimentally significantly different radiograph, some characteristic features appear in the final radiograph and the inspector rejects the proof. (b) Each pixel represents the bubble count from a single superheated (droplet) bubble detector. Graphics from: Nature Communications article, CC BY the Authors.

How does our system looks like?

Our current set-up is located at the Princeton Plasma Physics Laboratory. It consists of a collimated fast neutron beam, a 1D array of superheated droplet (bubble) detectors and an object holder where we arrange 2”-cubes of different materials in different patterns. The system allows to perform zero-knowledge comparison of these different patterns.

The first iteration of our zero-knowledge object-comparison set-up. Graphics from: Nature Communications article, CC BY the Authors.

What is next?

We have recently performed measurements on highly enriched uranium at the Nevada National Security Test Site, we are now analyzing the results. We are building a new iteration of the system located at PPPL including a new collimator housing our new and more powerful neutron generator. The goal is to allow for both transmission and neutron-induced emission measurements at the same time. We are also developing a new bubble reader to increase our measurement statistics and be able to distinguish smaller variations between objects. Francesco d’Errico at Yale university is providing R&D support by designing new detectors for our next round of experiments. Finally, we plan to design a field version of the setup with the support of the full motion virtual reality project’s team.


We are thankful to our past and current sponsors including: U.S. Department of Energy’s National Nuclear Security Administration through the Consortium for Verification Technology, John D. and Catherine T. MacArthur Foundation, the Carnegie Foundation of New York, Global Zero, The Simons Foundation, and U.S. Department of State Verification Assets Fund.

Further readings

Journal Articles:
S. Philippe, R. Goldston,A. Glaser, and F. d’Errico, A physical zero-knowledge object-comparison system for nuclear warhead verification, Nature Communications, 7:12890 doi: 10.1038/ncomms12890 (2016).

A. Glaser, B. Barak, and R. Goldston, A Zero-knowledge Protocol for Nuclear Warhead Verification, Nature, 510 (2014): 497-502.

Selected Conference Papers:
S. Philippe, R. J. Goldston, A. Glaser and F. d’Errico, “Zero-Knowledge Differential Isotopic Comparison of Special Nuclear Materials,” 57th Annual INMM Meeting, 24-28 July 2016, Atlanta, Georgia.

S. Philippe, B. Barak and A. Glaser, “Designing Protocols for Nuclear Weapons Verification,” 56th Annual INMM Meeting, 12-16 July 2015, Indian Wells, California.

Yan Jie and A. Glaser, Two-Color Neutron Detection for Zero-Knowledge Nuclear Warhead Verification, 56th Annual INMM Meeting, July 12-16, 2015, Indian Wells, California.

M. Kütt , S. Philippe, B. Barak, A. Glaser and R. J. Goldston, Authenticating Nuclear Warheads With High Confi dence, 55th Annual INMM Meeting, 20-24 July 2014, Atlanta, Georgia.

R. J. Goldston, F. d’Errico, A. di Fulvio, A. Glaser, S. Philippe and M. Walker, Zero-Knowledge Warhead Verification: System Requirements and Detector Technology, 55th Annual INMM Meeting, 20-24 July 2014, Atlanta, Georgia.

On zero-knowledge proofs:

A zero-knowledge object-comparison set-up. Image Credit: (c) Nuclear Futures Laboratory