Post-Quantum Cryptography (PQC): The Shift to Quantum-Resistant Encryption

Progress in quantum computing poses a fundamental threat to the asymmetric cryptography that secures nearly all internet traffic today. Shor's algorithm can mathematically break RSA and elliptic-curve keys in timescales that can no longer be dismissed as impossible.

What is at risk, and what is not

The distinction is often blurred. What is genuinely at risk is public-key cryptography — RSA, Diffie-Hellman, and elliptic curves — whose security rests on the difficulty of factoring large numbers and the discrete logarithm problem. Both are exactly the kind of problem Shor's algorithm solves.

Symmetric cryptography such as AES holds up far better. Grover's algorithm does speed up key search, but only quadratically: AES-256 remains secure, and AES-128 merely drops to roughly 64-bit strength. Hash functions are in a similar position. Lengthening symmetric keys is enough; public key requires entirely different mathematics.

The standards are already final

NIST has formalised lattice-based algorithms as its post-quantum defence standard. ML-KEM handles key exchange, ML-DSA handles digital signatures. Their security rests on lattice problems for which no efficient quantum algorithm is known.

The practical consequence to plan for is size. Post-quantum public keys and signatures are far larger than their elliptic-curve equivalents — in some cases dozens of times larger. For TLS certificates, that gap adds overhead to every new connection.

Why waiting is not an option

The most urgent reason is not a quantum computer that already exists, but a strategy known as harvest now, decrypt later. Encrypted traffic can be recorded today and stored until a machine capable of opening it becomes available.

The arithmetic is simple: if your data must still be secret ten years from now, and a cracking machine is expected within that window, then data sent today is already at risk. Medical records, trade secrets, and state archives fall squarely into this category.

Realistic steps

Migration starts with an inventory, not with replacement. Most organisations do not really know where asymmetric cryptography is used — certificates, code signing, VPNs, session tokens, third-party integrations.

Hybrid schemes are the safest transition path: combining elliptic curves with post-quantum algorithms so that a connection stays secure as long as either one holds. The approach protects on two fronts at once — from future quantum computers, and from the possibility that a weakness is found in new algorithms the world has not tested for long.