“This paper is saying that if certain other conjectures are true, then quantum cryptography must exist,” Ma said. These quantum locks could potentially remain secure even if all classical locks are easy to break. If researchers complete the proof that quantum computers truly surpass classical ones at a specific task, that will automatically put quantum cryptography on much stronger theoretical footing than practically any kind of classical cryptography. Meanwhile, other researchers have devised quantum cryptography methods that could be used sooner, though more work will be needed to establish that they’re truly secure. Quantum cryptography has already proved full of surprises, and researchers have only recently begun exploring the possibilities.