The Promise and Peril of Our Quantum Future: Craig Costello (Transcript)

Craig Costello at TEDxSydney

Here is the full text of cryptography researcher Craig Costello’s talk titled “The promise and peril of our quantum future” at TEDxSydney conference.

Craig Costello – Microsoft Research

I’m in the business of safeguarding secrets, and this includes your secrets.

Cryptographers are the first line of defense in an ongoing war that’s been raging for centuries: a war between code makers and code breakers. And this is a war on information.

The modern battlefield for information is digital. And it wages across your phones, your computers and the internet. Our job is to create systems that scramble your emails and credit card numbers, your phone calls and text messages — and that includes those saucy selfies — so that all of this information can only be descrambled by the recipient that it’s intended for.

Now, until very recently, we thought we’d won this war for good.

Right now, each of your smartphones is using encryption that we thought was unbreakable and that was going to remain that way. We were wrong, because quantum computers are coming, and they’re going to change the game completely.

Throughout history, cryptography and code-breaking has always been this game of cat and mouse. Back in the 1500s, Queen Mary of the Scots thought she was sending encrypted letters that only her soldiers could decipher.

But Queen Elizabeth of England, she had code breakers that were all over it. They decrypted Mary’s letters, saw that she was attempting to assassinate Elizabeth and, subsequently, they chopped Mary’s head off.

A few centuries later, in World War II, the Nazis communicated using the Enigma code, a much more complicated encryption scheme that they thought was unbreakable.

But then good old Alan Turing, the same guy who invented what we now call the modern computer, he built a machine and used it to break Enigma. He deciphered the German messages and helped to bring Hitler and his Third Reich to a halt.

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And so the story has gone throughout the centuries. Cryptographers improve their encryption, and then code breakers fight back and they find a way to break it. This war’s gone back and forth, and it’s been pretty neck and neck.

That was until the 1970s, when some cryptographers made a huge breakthrough. They discovered an extremely powerful way to do encryption called “public-key cryptography.”

Now, unlike all of the prior methods used throughout history, it doesn’t require that the two parties that want to send each other confidential information have exchanged the secret key beforehand. The magic of public-key cryptography is that it allows us to connect securely with anyone in the world, whether we’ve exchanged data before or not, and to do it so fast that you and I don’t even realize it’s happening.

Whether you’re texting your mate to catch up for a beer, or you’re a bank that’s transferring billions of dollars to another bank, modern encryption enables us to send data that can be secured in a matter of milliseconds.

The brilliant idea that makes this magic possible, it relies on hard mathematical problems. Cryptographers are deeply interested in things that calculators can’t do. For example, calculators can multiply any two numbers you like, no matter how big the size.

But going back the other way — starting with the product and then asking, “Which two numbers multiply to give this one?” — that’s actually a really hard problem.

If I asked you to find which two-digit numbers multiply to give 851, even with a calculator, most people in this room would have a hard time finding the answer by the time I’m finished with this talk.

And if I make the numbers a little larger, then there’s no calculator on earth that can do this. In fact, even the world’s fastest supercomputer would take longer than the life age of the universe to find the two numbers that multiply to give this one.

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