Bas Westerbaan

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Sizing Up Post-Quantum Signatures

Sizing Up Post-Quantum Signatures
Sizing Up Post-Quantum Signatures

Quantum computers are a boon and a bane. Originally conceived by Manin and Feyman to simulate nature efficiently, large-scale quantum computers will speed-up innovation in material sciences by orders of magnitude. Consider the technical advances enabled by the discovery of new materials (with bronze, iron, steel and silicon each ascribed their own age!); quantum computers could help to unlock the next age of innovation. Unfortunately, they will also break the majority of the cryptography that’s currently used in TLS to protect our web browsing. They fall in two categories:

  1. Digital signatures, such as RSA, which ensure you’re talking to the right server.
  2. Key exchanges, such as Diffie–Hellman, which are used to agree on encryption keys.

A moderately-sized stable quantum computer will easily break the signatures and key exchanges currently used in TLS using Shor’s algorithm. Luckily this can be fixed: over the last two decades, there has been great progress in so-called post-quantum cryptography. “Post quantum”, abbreviated PQ, means secure against quantum computers. Five years ago, the standards institute NIST started a public process to standardise post-quantum signature schemes and key exchanges. The outcome is expected to be announced early 2022.

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