QUANTUM CRYPTOGRAPHY
commonly used works in a post-quantum setting. “We still don’t know that. It doesn’t mean it is not safe, but we can’t be certain,” he says. It is why computers should come to the rescue.
You have to invent a language
anything at the end, a formula is a lot like a picture in this way. Online whiteboards are not the same either, so the pandemic has been challenging in that sense as well.”
Teaching the computer The other matter that interests Unruh and his colleagues is formal verification. No matter what kind of cryptography we are discussing, scientists need to make sure that it is resolutely secure. It needs to have a mathematical proof. It says rather simply, in this system, the communication cannot be hacked. “The problem is people make mistakes and proofs are very complicated. Whether it’s the person who writes the proof or the one that reads it and verifies it, neither one might not notice a flaw. It’s like finding a needle in a haystack, but that one mistake might change everything and make a system flawed,” Unruh explains. He adds that in research papers there are constantly errors. In many cases, they can be corrected and they don’t mean that much, but they can have a very serious and detrimental impact as well. Verification loses its meaning when we just hope that these complicated calculations are Estonian Centre of Excellence in ICT Research
correct. Even when you really are focused, you still might make a mistake. “One solution is to have a computer do the proof, but first you need to somehow explain the proof to a computer. One thing computers are – they are very careful. You can’t explain a proof to a computer when you have made a mistake. It is very complicated, but essentially when a computer understands you, you have succeeded,” Unruh describes.
A tragic experience Unruh shares a painful experience from his own not so distant past. He wrote an article about 70 pages in length and put it up online, not yet published in any magazine. “Someone wrote to me, that on page 50 there’s a formula that he doesn’t understand how it works. I checked and realised that I had made a little mistake. But it was still a tragic one, three months of hard work straight down the drain. I was lucky it was discovered, he was the only one who wrote to me. If no one had noticed the mistake, everyone would have believed the article. But it was a very important proof for quantum cryptography,” he recalls. It tried to prove that one hash function that is
How do you explain quantum cryptography to a computer, so it can ensure the proof is correct? Like most computer-related solutions, you have to write a program. For that, Unruh’s team has developed its own language. You must teach the computer what a secure system is, so what are the logical set of rules when making a security proof? The translation for a computer is ten times longer than it would be for a human and all of it written in an artificial language. Unruh’s work is to make the language easier and easier. It may never be as compact as the human version, but Unruh hopes they are getting closer and closer. “I don’t want my research team to be the only one able to make security-proofs like that, because there is a lot of crypto around us. My job is to make the tools, the infrastructure that others can use as well.” Unruh’s team has already found a
You can’t explain a proof to a computer when you have made a mistake. It is very complicated, but essentially when a computer understands you, you have succeeded. method and performed a non-trivial security proof, which was a considerable effort. While it worked, it would be challenging to convince others to use it, they must find a better way. He says that there are some aspects that computers are better at then we are. An easy example - you want to prove that one big number multiplied
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