The unique model of this story appeared in Quanta Journal.
Arduous issues are normally not a welcome sight. However cryptographers love them. That’s as a result of sure laborious math issues underpin the safety of recent encryption. Any intelligent trick for fixing them will doom most types of cryptography.
A number of years in the past, researchers discovered a radically new strategy to encryption that lacks this potential weak spot. The strategy exploits the peculiar options of quantum physics. However not like earlier quantum encryption schemes, which solely work for a couple of particular duties, the brand new strategy can accomplish a a lot wider vary of duties. And it may work even when all the issues on the coronary heart of odd “classical” cryptography grow to be simply solvable.
However this hanging discovery relied on unrealistic assumptions. The end result was “extra of a proof of idea,” mentioned Fermi Ma, a cryptography researcher on the Simons Institute for the Concept of Computing in Berkeley, California. “It isn’t an announcement about the actual world.”
Now, a new paper by two cryptographers has laid out a path to quantum cryptography with out these outlandish assumptions. “This paper is saying that if sure different conjectures are true, then quantum cryptography should exist,” Ma mentioned.
Fortress within the Sky
You’ll be able to consider trendy cryptography as a tower with three important elements. The primary half is the bedrock deep beneath the tower, which is made from laborious mathematical issues. The tower itself is the second half—there you will discover particular cryptographic protocols that allow you to ship non-public messages, signal digital paperwork, forged secret ballots, and extra.
In between, securing these day-to-day purposes to mathematical bedrock, is a basis made from constructing blocks referred to as one-way features. They’re chargeable for the asymmetry inherent in any encryption scheme. “It’s one-way as a result of you may encrypt messages, however you may’t decrypt them,” mentioned Mark Zhandry, a cryptographer at NTT Analysis.
Within the Eighties, researchers proved that cryptography constructed atop one-way features would guarantee safety for a lot of totally different duties. However a long time later, they nonetheless aren’t sure that the bedrock is powerful sufficient to assist it. The difficulty is that the bedrock is made from particular laborious issues—technically often known as NP issues—whose defining characteristic is that it’s straightforward to test whether or not any candidate resolution is appropriate. (For instance, breaking a quantity into its prime components is an NP drawback: laborious to do for giant numbers, however straightforward to test.)
Many of those issues appear intrinsically troublesome, however pc scientists haven’t been in a position to show it. If somebody discovers an ingenious algorithm for quickly fixing the toughest NP issues, the bedrock will crumble, and the entire tower will collapse.
Sadly, you may’t merely transfer your tower elsewhere. The tower’s basis—one-way features—can solely sit on a bedrock of NP issues.
To construct a tower on more durable issues, cryptographers would wish a brand new basis that isn’t made from one-way features. That appeared unattainable till just some years in the past, when researchers realized that quantum physics may assist.
