The first time I stumbled upon the concept of Quantum Cryptography was in the Computer Networks book in my third year of engineering. I immediately found it fascinating and wondered if we would ever come to a point where it wouldn’t just be theoretical – Applied Quantum Cryptography, imagine the possibilities!
So, what is Quantum Cryptography?
Quantum cryptography relies on the foundations of quantum mechanics, in contrast to traditional public key cryptography, which relies on the computational difficulty of certain mathematical functions and cannot provide any indication of eavesdropping at any point in the communication process, or any mathematical proof as to the actual complexity of reversing the one-way functions used.
In simpler terms, traditional cryptography cannot tell if it has been compromised. It cannot also guarantee that one will not be able to reverse engineer the encryption algorithm. Quantum cryptography fixes both these problems, theoretically.
Quantum Key Distribution
One of the most notable applications of quantum cryptography is Quantum Key Distribution (QKD), which is the process of using quantum communication to establish a shared key between two parties (Alice and Bob, for example) without a third party (Eve) learning anything about that key, even if Eve can eavesdrop on all communication between Alice and Bob. If Eve tries to learn information about the key being established, discrepancies will arise causing Alice and Bob to notice.
Moreover, the security of quantum key distribution can be proven mathematically without imposing any restrictions on the abilities of an eavesdropper, something not possible with classical key distribution.
So, in theory, quantum cryptography seems to be a successful turning point in the information security sector. However, no cryptographic method can ever be absolutely secure. In practice, quantum cryptography is only conditionally secure, dependent on a key set of assumptions – for instance, we assume that the laws of quantum mechanics apply and that Alice and Bob are able to authenticate each other, i.e. Eve should not be able to impersonate Alice or Bob as otherwise a man-in-the-middle attack would be possible.
There are currently four companies offering commercial quantum key distribution systems; ID Quantique (Geneva), MagiQ Technologies, Inc. (New York), QuintessenceLabs (Australia) and SeQureNet (Paris). Practical applications still use sources that generate multiple photons. Key to the success of quantum cryptography would be the ability to develop a perfect single-photon source.
If you would like to learn more about Quantum Cryptography, read about BB84.