An Implementation of Zero Knowledge Confirmation using a Two- dimensional Time-Encoded Imaging System

In this paper we present an authenticatable verification measurement using two-dimensional time-encoded imaging (2D-TEI) to confirm the declaration of treaty accountable items (TAIs). 2D-TEI consists of a single (or few) detector pixel(s) surrounded by a rotating cylindrical coded mask. The mask pattern that is normally projected onto a position-sensitive, highly-pixelated detector in traditional coded-aperture imaging becomes time encoded in the modulated rate of the pixel(s). High resolution fast neutron 2D-TEI has recently been demonstrated in proof of concept measurements of extended fission sources. We will show that a 2D-TEI with a properly designed coded mask will exhibit an unmodulated detection rate if and only if two objects placed on opposing sides of the system are identical in geometry and activity. Because a positive is indicated by a null result and no sensitive information must be “pre-loaded”, 2D-TEI is an ideal candidate technology for Zero-Knowledge Protocols (ZKP). In recent years, the concept of ZKP as a useful approach to nuclear warhead verification has become increasingly popular. Several implementations of ZKP have been proposed, driving technology development toward proof of concept demonstrations. Last year the authors, along with several experts at Sandia National Laboratories presented an analysis of the benefits and challenges of ZKPs over more traditional warhead verification approaches. Whereas proposed physical implementations seemed to fall within the general class of template-based techniques, it was the procedural elements of ZKPs that offer many benefits. By introducing the choice between several presented objects, one of which may be a pre-authenticated reference TAI, the inspecting party gains statistical confidence that all objects are identical over many trials. However, all physical implementations of ZKPs proposed to date have a complication: once the instrumentation is prepared, it is no longer authenticatable; the instrument physically contains sensitive information. An ideal implementation of ZKP would include a comparison measurement that can be monitored during confirmation. We will show that a properly designed 2D-TEI can provide just such a measurement: because a positive is indicated by a constant rate at all times, the monitoring party can be allowed full access to the instrument before, during, and after confirmation.