Exploring Quantum Key Distribution

The first time I heard about the application of Quantum physics in cryptography outside of physics labs was when Swiss election authorities used quantum cryptography, or more specifically Quantum Key Distribution (QKD), to protect ballots cast in the 2007 parliamentary elections of the Geneva region.

Wikipedia defines QKD as follows:

QKD describes the process of using quantum communication to establish a shared key between two parties (usually called Alice and Bob) without a third party (Eve) learning anything about that key, even if Eve can eavesdrop on all communication between Alice and Bob. This is achieved by Alice encoding the bits of the key as quantum data and sending them to Bob; if Eve tries to learn these bits, the messages will be disturbed and Alice and Bob will notice. The key is then typically used for encrypted communication.

So the key (pardon the pun!) difference between more traditional cryptography and QKD is that while security in the former is achieved based on the assumption that the attacker won’t be able to solve a mathematical problem (e.g. prime factorization in case of RSA), QKD relies on laws of quantum physics to achieve security. Basically, even if an attacker manages to intercept communications, it will inevitably leave a trace and hence alert the other parties to the intercept. This makes the traditional man in the attacks a thing of the past.

You might be wondering why this seemingly great technology is not more widespread. A big part of the answer is really the engineering challenge and infrastructure requirements inherent to quantum cryptography. Use of photons to share keys between parties in QKD necessitates use of dedicated fiber optic line between the two. In addition to that, instability of quantum states in entangled photons limits on the maximum usable distance of these lines, at least with today’s technology.

Then again, as with any cutting edge technology, there are challenges to solve and as long as there is a commercial interest in “unbreakable” encryption, all problems are solvable. In that regard, the QKD industry is attracting capital investments and over the next couple of years we will see much more commercial as well as R&D focused developments in this area, particularly in Europe and North America. Case in point, Ohio-based Battelle Memorial Institute in cooperation with ID Quantique (the QKD vendor that helped with Swiss elections) is developing one of the largest such key distribution networks around Columbus, OH and is planning to use quantum repeaters to mitigate the range limitations.

Read more about this very recent development at Fortune.

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