What is post-quantum cryptography?

Post-quantum cryptography (PQCPQC: post-quantum cryptography. Encryption designed to stay secure against future quantum computers.) is public-key cryptography designed to stay secure against a large quantum computer while running on ordinary computers. NIST published the first standards on 13 August 2024: FIPS 203 (ML-KEM) for establishing keys, and FIPS 204 (ML-DSA) and FIPS 205 (SLH-DSA) for digital signatures. They rest on mathematical problems, such as finding short vectors in high-dimensional lattices, or on the security of hash functions, for which no efficient quantum attack is known. Migrating means updating software, libraries, protocols and certificates, not buying quantum hardware. It is also not the same as quantum key distribution, which needs special optical equipment. The price of the change is size: post-quantum keys and signatures are larger than today's, so handshakes grow and some old equipment struggles. Most organisations meet PQC first through updates of browsers, operating systems and VPN software, and then have to deal with their own servers and applications.

This answer is part of the guide: Post-quantum readiness: where to start

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