Inside the quest for unbreakable encryption

The last three decades of cybersecurity have played out like an increasingly intricate game, with researchers perpetually building and breaking—or attempting to break—new candidates.

A few years back, researchers at Google and the KTH Royal Institute of Technology, in Sweden, estimated that it would take a quantum computer composed of 20 million quantum bits, or qubits, some eight hours to break today’s 2,048-bit RSA security. Current state-of-the-art machines are nowhere close to that size: the largest quantum computer to date, built by IBM, debuted last year with 433 qubits.

Whether or not RSA can be considered at immediate risk of a quantum attack depends largely on whom you ask, says computer scientist Ted Shorter, who cofounded the cybersecurity company Keyfactor. He sees a cultural divide between the theorists who study the mathematics of encryption and the cryptographers who work in implementation.

To some, the end seems nigh. “You talk to a theoretical computer scientist and they’re like, Yes, RSA is done, because they can imagine it,” Shorter says. For them, he adds, the existence of Shor’s algorithm points to the end of encryption as we know it. 

Many cryptographers who are implementing real-world security systems are less concerned about the quantum future than they are about today’s cleverest hackers. After all, people have been trying to factor efficiently for thousands of years, and now the only known method requires a computer that doesn’t exist. 

Thomas Decru, a cryptographer at KU Leuven in Belgium, says the quantum threat must be taken seriously, but it’s hard to know if RSA will fall to quantum computers in five years or longer—or never. “As long as quantum computers do not exist, everything you say about them is speculative, in a way,” he says. Pass is more certain about the threat: “It’s safe to say that the existence of this quantum algorithm means there are cracks in the problem, right?” 

The thorns of implementation

But we have to be ready for anything, says Lily Chen, a mathematician who manages NIST’s Cryptographic Technology Group and works on the ongoing effort to produce post-quantum encryption standards. Whether they arrive in three years or 30, quantum computers loom on the horizon, and RSA, Diffie-Hellman, and other encryption schemes may be left vulnerable. 

Finding a quantum-resistant cryptographic scheme isn’t easy. Without a mathematical problem that is computationally hard, the last three decades of cybersecurity have played out like an increasingly intricate game, with researchers perpetually building and breaking—or attempting to break—new candidates. 

This push and pull has already emerged in the NIST post-quantum program. In February 2022, cryptographers found a fatal flaw in Rainbow, an algorithm that had survived three rounds of NIST’s analysis. A few months later, after the NIST list had been winnowed again, Decru and his KU Leuven colleague Wouter Castryck announced that they’d broken another finalist, an algorithm called SIKE.