Physically secure and fully reconfigurable data storage using optical scattering

This paper presents an optical method of storing random cryptographic keys within a reconfigurable volume of polymer-dispersed liquid crystal (PDLC). We suggest a PDLC-based device that functions as an integrated optical physical unclonable function (PUF). Our device can selectively access a dense set (up to 10 Gb/mm³ in theory) of non-electronically saved random bits. Furthermore, this optical PUF can fully erase and transform these bits into a new random configuration in less than one second, via a simple electrical signal. When a short voltage spike is applied across the PDLC film interface, its optical scattering potential completely decorrelates. We confirm this phenomenon with detailed experiments on a proof-of-concept device, thereby suggesting the security use of a new class of optical materials as (i) securely and efficiently reconfigurable PUFs, and (ii) an erasable storage medium for random cryptographic keys. Our work can eventually help address the challenge of quickly and completely erasing sensitive digital electronic memory and/or key material. It also establishes a new and hopefully fruitful connection between security questions and the material sciences.