From spy thrillers to laser beams: creating an unbreakable code

Worldwide, spending on cyber security is skyrocketing with at least 16 billion online records exposed in the first half of 2020 alone.

But our current methods for safeguarding information don’t protect us from the biggest security threat looming around the corner: the inevitable breakdown of all encryption systems with increased computing power.

To find a solution, ANU researchers are looking to the realm of quantum physics. And laser beams.

According to the theory of quantum mechanics, the laws of nature start behaving very strangely at the quantum scale – the miniscule realm of the atomic and sub-atomic, and so strange Einstein deemed them to be just plain “spooky”.

Professor Ping Koy Lam from the ANU Research School of Physics is less interested in spooky and more interested in harnessing a measurable quantum phenomenon: randomness.

“One thing we do in our labs is create random numbers using a laser beam,” he says.

To understand why Professor Lam’s lasers are so important to cyber security, we first need to go back to the Cold War.

Back then, KGB spies used an encryption method developed in the early 1900s known as one-time pad, where a random string of numbers shifts the position of letters of the alphabet.

Two spies would get identical note pads, each with the same string of random numbers on the first page. After writing or reading an encoded message, you would destroy the list of random numbers.

“If another person intercepted the whole encrypted message, the message would just be a random shuffle of letters that didn’t mean anything,” Professor Lam says.

This type of encryption has a major benefit over others; if the random numbers are only used once, there is no mathematical way to decode the message.

Apart from one-time pad, most other current encryption methods rely on mathematical complexity.

“Some mathematical functions are easier to solve going one way and harder to solve going the other way,” Professor Lam explains.

But these methods are far from perfect.

“If you have a big enough computer you may, by chance, eventually break the code,” Professor Lam says. “So modern encryption security is dependent on the resources you have. Organisations that are well resourced have an information advantage over organisations that are poorly resourced.”

“If you get quantum encryption working properly, you can only break the code if the laws of physics themselves are broken.”

Professor Ping Koy Lam

On top of this, government and industry are counting down the days until the inevitable development of quantum computers, which will be powerful enough to break current mathematical encryption even faster.

One-time pad doesn’t rely on mathematical complexity. Professor Lam says this century-old technique can be applied to modern computing and is proven to be absolutely secure. Unless, of course, you have access to the original string of random numbers.

“Some organisations used to generate one-time pads,” he says. “They then took a physical copy of the random numbers, via someone handcuffed to a briefcase delivering them to a secure location.”

Obviously, there are many ways to compromise this kind of information security protocol.

“What if the random numbers are duplicated? What if someone sells your random numbers?” Professor Lam says.

This is where Professor Lam’s laser beam comes in. Light could allow for truly random numbers to be sent across the globe by harnessing the peculiar behaviour of quantum particles such as the photons of a laser beam.

“If you turn on a laser beam, and if you measure it with high accuracy, you can record fluctuations in the brightness of light,” Professor Lam says.

“What we do is encode random numbers on the beam of a laser light, and we send that laser light to a receiver.”

As this information is encrypted in the laser beam, nobody can intercept the message; if an eavesdropper disrupts the laser beam, the act will be revealed to both the sender and the receiver. The string of random numbers will subsequently be discarded from use.

“If you get quantum encryption working properly, you can only break the code if the laws of physics themselves are broken,” Professor Lam says.

“So, if our understanding of the laws of physics is correct, we have an unbreakable code.”