Over the centuries, people have continually explored new encryption methods to keep sensitive information confidential, with one technique replacing another. The first methods were based on replacing letters or numbers. World War II saw the advent of encryption machines, including the famous Enigma. Since then, things have gained speed with advances in computing and, more recently, in quantum physics.
The next advance could well come from… light.
Researchers at the Technical University of Darmstadt, Germany, are indeed suggesting using the properties of non-polarized light as a new method of encryption. For this they use a still emerging technique called Ghost Polarization Communication (GPC).
Light is made up of a magnetic field and an electric field. In the case of polarized light (such as lasers), the orientation of the magnetic field is fixed. Conversely, with non-polarized light (sunlight, LED lamps), the orientation of the magnetic field varies randomly… about once every nanosecond.
In this way, non-polarized light can very rapidly generate a series of random numbers (strings of 0s and 1s) that will be used to encrypt a message.
The data communicated are encrypted in a light beam and to decipher them all that is needed is to send a second unmodified light beam, then to compare their respective polarization angles.
Thus, only the legitimate recipient who has access to the reference beam can decipher the message, which removes any possibility of interception. This is known as “ghost” polarization.
The end of RSA encryption?
In order to validate this concept, the Darmstadt researchers used standard commercial equipment, including optical fibre cable and 1550 nm light sources. This bodes well for ease of access to this new encryption technique, over 175 years after the discovery made by Sir Gabriel Stokes, the “father” of polarization.
Testing is still in the early stages and it is necessary to refine the approach by increasing modulation and transmission speeds, as was done previously for other encryption techniques, which started off with small speeds, gradually increasing these with time.
Such was the case for example of the chaos-based cryptography used for coding and decoding high speed telecommunications. It is possible to make an analogy between GPC and this because it consists in adding a chaotic signal to the message to be transmitted. As they know the characteristics of the initial chaotic signal, only the recipient can extract the message from the signal received.
Should it be a success, Ghost Polarization Communication could be used as an alternative to traditional cryptographic technologies and in particular the inescapable RSA method (asymmetric cryptography) on which many communication protocols are based, such as the notorious SSL/TLS that secure our web browsing.
Quoted on the IEEE Spectrum website, Robert Boyd, a professor of optics at the University of Rochester, in New York, believes that if GPC turned out to be more secure or more efficient to implement – even by a factor of two – it would have a tremendous advantage over RSA.
It could then become an alternative to quantum cryptography and chaotic communications.
In the area of the Internet of Things (IoT), this “crypto light” would enable private messages to be exchanged between two connected objects without the need for human intervention.
One can also imagine the pairing of GPC with Li-Fi (light fidelity), a wireless communications technology via the light emitted by a LED light. GPC would reinforce even more the protection of this “internet by light” which, as it cannot go through walls as Wi-Fi does, already presents a particularly secure environment.