In 1948, Claude Shannon proved that information could be securely encrypted and transmitted given a single-use, randomly generated key. As long as the key – commonly referred to as a ‘one-time pad’ – is used only once, and is equal in length to the message it is encrypting, the message would be impossible to crack. Quantum data locking presents a new, more efficient means of data encryption in which the key can be significantly shorter than the message while maintaining perfect secrecy.

Quantum data locking works by transmitting coded messages using particles of light, or photons. Because photon waves can be altered in a number of different ways – the wavelength can be modified, the amplitude can be adjusted – there are intrinsically more variables than in the traditional binary scheme in which something is either ‘on’ or ‘off.’ These additional variables – combined with quantum uncertainty principles which suggest that you cannot simultaneously know about all of the variables at once – allow for much shorter encryption keys.

A team of researchers at the University of Rochester has developed a new machine which successfully demonstrates quantum data locking. The machine works by generating photons and sending them through a spatial light modulator (SLM) which alters the various properties of the photon. A receiver of the message would need the key which describes how to use their own SLM to modify the photons back into their original form.  An eavesdropper who intercepts the transmission has only one shot at deciphering the message as the quantum nature of the system implies that a single measurement changes the system itself, and thus destroys the original message.

While the successful implementation of quantum data locking ushers in a new era of information theory, there are still a number of challenges associated with this technique. For starters, there must be a way for the initial key to be shared between parties. Once that hurdle is overcome, however, quantum data locking uniquely allows for subsequent keys to be appended to each additional message indefinitely. Finally, this particular implementation relies on the propagation of photons through air, which is impractical for long-distance applications. In such cases, fiber optic transmission is preferable, but would require a new means of scrambling the photons.

Acknowledgements: Many thanks to Shimon Kolkowitz, a physicist at NIST in Boulder, CO and Michael Goldman, a graduate student in the Harvard Physics department for their extremely helpful insight and expertise on the subject.

Managing Correspondent: Tarraneh Eftekhari

Scientific Paper: Quantum Enigma Machine: Experimentally demonstrating quantum data locking

Media Coverage: Experiment Confirms Plan for Quantum Coded-Messages – ScienceNews