Passive gamma spectroscopy has been successfully used for inspection systems based on the template-matching approach. The most prominent example of such a system is Sandia's Trusted Radiation Identification System (TRIS), which is based on an earlier system used at Pantex since 1994 to confirm the identities of containerized pits. Additional experiments have shown that "template matching can be performed in a way that is robust and does not reveal classified information" (TRIS User's Manual). Remarkably, TRIS uses only 16 energy bins, i.e., 16 numbers, to accomplish this task. Apart from establishing confidence in the authenticity of the information-barrier hardware, there exists a separate challenge establishing and maintaining confidence in the template, i.e., in the data characterizing the treaty accountable item. In the case of TRIS, the template data is stored on a Dallas iButton® made by Maxim Integrated Products, Inc. Here, we propose an inspection protocol that uses a different approach: while some data remains secret, other data is shared between both parties and is, in fact, made public. In our approach, information is stored in the form of punched cards that encode the secret template. Public masks can be used to reveal selected features of the template, constraining certain properties of the treaty accountable item and providing increasing levels of transparency. We demonstrate the concept using Princeton's Information Barrier Experimental II, which is based on a vintage 6502 processor.
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