Post-Quantum Cryptography

Post-quantum cryptography (PQC) is the branch of cryptography concerned with designing algorithms that resist attack by both classical and quantum computers — specifically, algorithms whose hardness does not depend on integer factorization or discrete logarithm problems, which Shor's Algorithm solves in polynomial time on a sufficiently large quantum machine.

The leading candidates rely on the assumed hardness of problems in lattice mathematics (shortest vector problem, learning with errors), hash functions, error-correcting codes, and multivariate polynomial systems. NIST finalized the first four PQC standards in 2024. The transition from RSA and elliptic-curve infrastructure is the largest mandatory cryptographic migration in history — and most of it has not yet happened.

The central problem is not algorithm selection but key distribution and infrastructure inertia: billions of devices running legacy protocols, TLS libraries compiled against classical assumptions, and hardware security modules that cannot be updated in the field. Mathematics can be replaced overnight; systems cannot.