  We present an optical method of storing random cryptographic keys, at high
densities, within an electronically reconfigurable volume of polymer-dispersed
liquid crystal (PDLC) film. We demonstrate how temporary application of a
voltage above PDLC's saturation threshold can completely randomize (i.e.,
decorrelate) its optical scattering potential in less than a second. A unique
optical setup is built around this resettable PDLC film to non-electronically
save many random cryptographic bits, with minimal error, over a period of one
day. These random bits, stored at an unprecedented density (10 Gb per cubic
millimeter), can then be erased and transformed into a new random key space in
less than one second. Cryptographic applications of such a volumetric memory
device include use as a crypto-currency wallet and as a source of resettable
"fingerprints" for time-sensitive authentication.
