Quantum and the Magic Decoder Ring

What sparked governments’ interest in quantum computing was fear, or hope, of breaking secret codes. As they have learned more about it, other possibilities have drawn their attention. If you could easily break encryption, cybersecurity would be in much worse shape than it is today. Encryption is not just a tool that governments use to transmit secret messages to spies and soldiers. Encryption is ubiquitous, working behind the scenes in our web browsers, emails, databases, ATMs, and a lot more. Without encryption, it would be almost impossible to defend against hacking successfully. So, should we fear that quantum computing research will endanger cybersecurity?

If you thought quantum physics is complicated, the mathematics behind modern encryption can also quickly leave you in the dust. Again, we are going to simplify. Most encryption codes are based on a mathematical process called factoring: By what whole numbers can another, larger number be divided? So, for the number 12, the factors are 1, 2, 3, 4, 6, and 12. You can do that kind of factoring in your head, but it’s a lot harder when the number you are factoring is not just two digits (like the number 12) but, say, hundreds of digits.

Most encryption algorithms utilise factors (prime factors, to be precise of very large numbers as their basis. The assumption is that, even with a modern supercomputer trying out all the permutations, it could not correctly guess the factors that are being used as the basis for a particular encryption code without thousands of years of run time. If quantum computers can be made to work, thousands of years’ worth of conventional computing could be done in seconds and modern encryption could be cracked.

With that hope in mind, governments have been rumoured for years to be collecting and storing other nations’ encrypted messages that they now cannot crack. Someday, perhaps in the next few years, quantum computing might allow China, Russia, the U.K, or the U.S to read messages that they intercepted years ago, what you might think of as reading other people’s old mail or yesterday’s news. That may prove interesting and maybe even useful in the field of counterintelligence, tracking down spies and their sources. If and when this happens, don’t expect anyone to announce it. This is one aspect of the quantum computing race where no one is going to claim to be first across the finish line.

As for cracking encryption codes in use currently, remember that a functioning quantum computer, when it appears, will not be generally available any more than a supercomputer is today. No one would argue, however, that supercomputers are unimportant. Indeed, they are necessary for any number of important uses, including designing nuclear weapons. Quantum computers will be owned and operated only by governments and a few large companies. The governments that have them will be able to use them to revolutionize many aspects of science and technology, including cybersecurity. If you are not working in those governments of the few companies that will have a functioning quantum computer and you want to use one, you will have to access quantum machines in clouds operated by IBM, Google, Microsoft, and probably Rigetti. Sorry, but they are not going to let you rent time in their quantum cloud to decrypt Citibank’s codes.

Moreover, cryptologists, the mathematicians who live in the abstr