Rob Joyce, the director of cybersecurity at the NSA, said so in an interview:
The NSA already has classified quantum-resistant algorithms of its own that it developed over many years, said Joyce. But it didn’t enter any of its own in the contest. The agency’s mathematicians, however, worked with NIST to support the process, trying to crack the algorithms in order to test their merit.
“Those candidate algorithms that NIST is running the competitions on all appear strong, secure, and what we need for quantum resistance,” Joyce said. “We’ve worked against all of them to make sure they are solid.”
The purpose of the open, public international scrutiny of the separate NIST algorithms is “to build trust and confidence,” he said.
I believe him. This is what the NSA did with NIST’s candidate algorithms for AES and then for SHA-3. NIST’s Post-Quantum Cryptography Standardization Process looks good.
I still worry about the long-term security of the submissions, though. In 2018, in an essay titled “Cryptography After the Aliens Land,” I wrote:
…there is always the possibility that those algorithms will fall to aliens with better quantum techniques. I am less worried about symmetric cryptography, where Grover’s algorithm is basically an upper limit on quantum improvements, than I am about public-key algorithms based on number theory, which feel more fragile. It’s possible that quantum computers will someday break all of them, even those that today are quantum resistant.
It took us a couple of decades to fully understand von Neumann computer architecture. I’m sure it will take years of working with a functional quantum computer to fully understand the limits of that architecture. And some things that we think of as computationally hard today will turn out not to be.