The Quantum Credit Card
Sebastianus A. Goorden, Marcel Horstmann, Allard P. Mosk, Boris Škorić,, and Pepijn W.H. Pinkse
Credit cards, passports and other keys could, until now, be forged by either making a direct copy or by otherwise emulating the behavior of the key. The usual way to prevent this is by keeping the information encoded in the key hidden from attackers. We demonstrate Quantum-Secure Authentication (QSA)  of an optical physical key, which is secure even if an attacker knows everything about the key. Illumination of a multiple-scattering key with light that contains fewer photons than spatial degrees of freedom allows authentication of the key, while quantum-physical principles prohibit digital emulation. Therefore, QSA is secure if the physical key is impossible to copy, which is believed to be the case for sufficiently complex random media such as dried white paint . QSA forms a practical alternative to authentication methods that rely on keeping information about the key secret, which is very useful in modern society.
 S.A. Goorden et al., Optica 1, 421-424 (2014)
 R. Pappu et al., Science 297, 2026-2030 (2002)