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Of keys, codes and quantum computers

#### Written by Pieter Dilg

Imagine you are working on a top secret project and you have to send a message containing confidential information concerning the project. How can you make sure the message won’t be read by any other eyes than those of the addressee? A message that changes itself when read by anyone who is not supposed to, sounds like everything you need. Is this the future? No. It already exists. The quantum computer brings not only this, but also many other incredibly useful possibilities. What are quantum computers, and how can they shatter our present-day digital defences?

### Encryption

Digital security, whether it comes to protecting databases, sending confidential information or simply having a password login system, uses encryption in almost every case. Simply put, encrypting data is changing all the content into an unreadable combination of characters, with a special key needed to revert the data back to the original form. It is basically what we did when we were kids, making our own “secret” code. An example would be letting every letter correspond to a number, making you able to read the numbers only if you have a list of the combinations. Another example of a simple encryption algorithm is the “rot13” script, in which one replaces every letter with the 13th letter after it in the alphabet and vice versa:

It goes without saying that it becomes difficult quickly to manually unveil the encryption method that was used. A computer, however, is able to try enormous amounts of decryption keys in short amounts of time, to find the one that reverts it back to readable script. In this way, when you have enough of the encrypted data, a computer can unravel most encryptions, even though it may take a long time and lots of processing power. It is transparent that the stronger the computer (i.e. the more processing power it has), the faster it can try out different keys.
However, in its very essence, the regular computer can still carry out only one function at a time, albeit very quickly. Consequently, with billions of possible keys, it can take ages to find the right one. This is where the quantum computer comes in.

### The quantum computer

A quantum computer, as the name suggests, makes use of quantum mechanics. Quantum mechanics are incredibly difficult to understand, but the observable aspects themselves are easier to comprehend. Two specific quantum effects that particles show, are used by quantum computers:

• Entanglement of particles: pairs or groups of particles exist, wherein a particle’s state cannot be independently described of the state of the other(s), no matter the distance between them. Knowing about the state of one of the particles, means you know about the state of the other.
• Particles’ superposition: a particle that is in superposition could be in multiple states at the same time (e.g. having multiple angular momenta at the same time), and only when the particle is observed or measured, it will behave in one particular state.

Using these miraculous properties, a quantum computer is able to supply an enormous processing power. Where a bit in a normal computer can take on 0 or 1, the equivalent qubit in the quantum counterpart can take on both values at the same time. A quantum computer can thus carry out multiple tasks at the same time, increasing exponentially with the amount of qubits available. Back around 1980, scientists already described the concept of quantum computers and their many possible uses. Since 2016, there are actual machines running for test-purposes, and the producers stated they will become available on the market soon.

### Quantum criminals

As a quantum computer can carry out multiple tasks at the same time, it can crack most puzzles very quickly. Imagine a long password with many different characters. Guessing the right password may take an extremely long time, as there are millions or even billions of combinations. However, when not guessing passwords one after another, but many at the same time instead, the password’s ability to keep strangers out will eventually dwindle.
Similarly, strong quantum computers could also find the right key to decrypt data in mere seconds, in most cases. This means that almost any encrypted data would be legible to cyber criminals, were they to have a quantum computer available. However, as quantum computers are still very unstable and highly sensitive to environmental factors, such as movement and temperature, they do not form a big threat just jet. But just like the ordinary binary computer, they will surely keep evolving and one day, they may just fit inside a backpack.

### Fighting quantum with quantum

So are our modern digital security systems truly unable to cope with the upcoming quantum computers? The answer is yes. Luckily, however, the quantum mechanics can also be employed agàinst these key-cracking criminals. As I elaborated on in a previous article the keys generated for encryption are mainly created using random number generators. As regular computers cannot create truly random numbers, the encryption keys are pseudo-random most of the time, meaning they are easier to predict or guess. With the use of the superposition principle, intrinsically random numbers can be generated extremely fast. This technique has already been developed over time, and up to date the fastest true random number generator, created by Quintessence Labs, can produce a billion truly random numbers each second, using quantum mechanics.

This device is used by banks and government agencies around the world to greatly improve their digital security. This makes for extremely long true random sequences, that produce encryption keys incredibly difficult to crack, even with a quantum computer.
Another defence mechanism that some companies now apply, regards exchanging the keys. Sending encryption keys to the other party is a very risky operation, even when done with great care. There are many ways to intercept such intelligence, whether it is sent physically or over the internet. This technique of exchanging keys uses the fact the superposition of a particle is disrupted the moment it is observed or measured. It allows to send a key that changes or destroys itself when looked at in any way, except when done so at a specific destination.
With these clever mechanisms, and probably many more to come, we should, for the time being, be able to keep the bad guys out. Just remember to keep your computer updated!

Dit artikel is geschreven door: Pieter Dilg