Post-Quantum Cryptography

New cryptographic algorithms designed to resist attacks by large-scale quantum computers, replacing schemes a quantum computer would break.

The Coming Threat to Public-Key Crypto

Today's public-key cryptography, RSA and elliptic-curve schemes, rests on math problems that classical computers cannot solve in reasonable time: factoring large integers and computing discrete logarithms. A sufficiently large quantum computer running Shor's algorithm could solve both efficiently, breaking these systems outright. Post-quantum cryptography (PQC) replaces them with algorithms based on problems believed hard even for quantum machines.

The Mathematical Families

Kronos motion — safety factor

Lattice-based: security from hard problems in high-dimensional lattices
Hash-based: signatures built only from hash functions
Code-based: security from decoding random linear codes
Multivariate and isogeny-based approaches

After a multi-year public evaluation, standards bodies selected lattice-based schemes for general use, notably a key-encapsulation mechanism (ML-KEM) and a signature scheme (ML-DSA), alongside hash-based signatures for specialized needs.

Symmetric Crypto Is Less Affected

Symmetric ciphers like AES and hash functions like SHA-2 are not broken by quantum computers, only weakened. Grover's algorithm speeds up brute-force search quadratically, which is countered simply by using longer keys. The urgent migration is in public-key cryptography, not symmetric.

Hybrid Deployment

During the transition, systems often run hybrid schemes, combining a classical and a post-quantum algorithm, so security holds as long as either resists attack. This hedges against undiscovered flaws in the new algorithms while gaining quantum resistance.

Fusion Context

A fusion plant designed now will operate for decades, so long-lived secrets and firmware-signing keys should be chosen with post-quantum migration in mind. See why post-quantum matters for the harvest-now-decrypt-later problem that makes this relevant today rather than only after quantum computers arrive.