Quantum Computing has been projected to radically enhance computing power, which, at face value, sounds like a great advancement for the tech world. However, the increased power that brings quantum computing does come at a cost. Our current cryptographic techniques work fine for now, however, the power of quantum computing may leave our encrypted information up for grabs.

Currently, computers use the factorization problem to encrypt information. A secret key is shared between parties that is used to encrypt and decrypt information so that parties can share information without fear that someone else will be able to interpret their messages. The keys are numbers that can be factored into several other numbers. These numbers are the only trace that is left between key exchange. Therefore, in order to find the key number, a computer would have find out what the factors for the number are. Since factoring is problem in computer science that cannot be solved efficiently, keys generated this way have typically been safe to use. In fact, one of the strongest types of supercomputers would take 10123 times longer than the age of the universe to decrypt a standard encryption. The unreasonable resources needed to find a key through factorization currently make this method of cryptography safe to use.

The nature of quantum theory is that of uncertainty.

The power of quantum algorithms, however, threatens to decrease the amount of resources needed to factor numbers in order to find keys. Since a growing amount of our lives and communication is conducted through technology, cybersecurity is something that is of increasing importance. The promise of quantum algorithms breaking encryptions that were, reasonably, previously thought to be unbreakable is something that should be addressed in order to insure that important information remains encrypted. Luckily, quantum mechanics itself turns out to be a nearly perfect solution.

The nature of quantum theory is that of uncertainty. Measuring a quantum value, which is the polarization of a photon, changes the polarization of the photon, hence the polarization is uncertain before and after measurement. This is called the Uncertainty Principle. This principle is what makes quantum mechanics perfect for security purposes.

If you have ever read anything about cryptography, chances are you have met Alice, Bob, and the ever so nosey Eve. Cryptographic protocols are modeled on the classic scenario  that Alice – a theoretical party who wants to communicate secret messages –  shares a key with Bob, which she will use to encrypt a message. Bob can then use the key to decrypt the message. In the meantime, Eve tries to eavesdrop on Alice and Bob’s messages by stealing the key, so that she may decrypt the messages as well and understand what Alice and Bob are talking about.



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Now, say these keys are quantum keys. In the process of Eve measuring the key values, she is changing them! Alice and Bob, therefore, cannot settle on the key to use since the key value that Alice proposed is not the same as the key value that Bob received. So the messages sent cannot be picked up by an eavesdropping Eve since the key won’t be agreed upon. A key that is agreed upon means that it was not tampered with by Eve and is safe to use, while an unagreed upon key has been compromised. All Alice and Bob have to do is exchange keys until they agree upon one and then they can communicate freely without fear of Eve understanding what their messages are.

Though this is a very simplified model, this is the basic idea for quantum security protocols. The earliest, most successful quantum security protocol, called BB84, was created in 1984.The basic idea behind BB84 is more commonly referred to as Quantum Key Distribution (QKD). Since that initial protocol, protocols using QKD have been made even more secure by loosening some assumptions that BB84 made; however, the same basic idea of key exchange and agreement has lasted the test of time as the most secure method for doing quantum cryptography.

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Ayanna Matthews