If you read about quantum-safe security you will quickly meet two terms: quantum key distribution (QKD) and post-quantum cryptography (PQC). Both aim to keep communication secure once large quantum computers exist, but they work in completely different ways, need different skills and lead to different careers. This short guide explains the difference.
Why anything needs to change
Most of today’s secure connections use public-key cryptography such as RSA and elliptic-curve schemes to agree on keys and sign data. A large, fault-tolerant quantum computer running Shor’s algorithm could break these schemes. Such machines do not exist yet, but encrypted data can be recorded today and decrypted later, the so-called “harvest now, decrypt later” threat. That is why governments and companies are preparing now.
Post-quantum cryptography: new maths on ordinary computers
PQC replaces vulnerable algorithms with new ones based on mathematical problems that are believed to be hard even for quantum computers, such as problems on lattices, error-correcting codes or hash functions. PQC runs on the computers and networks we already have, so adopting it is mainly a software and hardware-implementation effort.
- NIST published its first three PQC standards on 13 August 2024: FIPS 203 (ML-KEM, for key establishment), FIPS 204 (ML-DSA, for signatures) and FIPS 205 (SLH-DSA, hash-based signatures). A standard based on FALCON is being developed as FIPS 206, and HQC was selected as an additional key-establishment algorithm on 11 March 2025.
- Strengths: it scales to every device and connection, and it does not need special hardware.
- Limits: its security rests on the assumption that the underlying maths problems stay hard, and migrating large systems takes years: organisations must find where cryptography is used, make it easy to swap algorithms (crypto-agility) and then replace it.
Quantum key distribution: security from physics
QKD uses single photons or weak laser pulses to create a shared secret key between two parties. Any attempt to measure the quantum states disturbs them and shows up as errors, so eavesdropping can be detected. The key is then used with conventional encryption.
- Strengths: its security does not depend on a maths problem staying hard, which matters for data that must remain secret for decades.
- Limits: it needs dedicated optical hardware and links. Fibre QKD is limited to a few hundred kilometres unless trusted relay nodes or satellites are used. It still needs classical cryptography to authenticate the parties, and real devices must be tested against implementation attacks, which is why certification projects such as the EU’s NOSTRADAMUS exist.
- Varieties: discrete-variable QKD uses single photons and single-photon detectors; continuous-variable QKD (CV-QKD) uses coherent light and telecom-style receivers; measurement-device-independent QKD removes detector vulnerabilities.
Not rivals, but layers
In practice most roadmaps use both. PQC is being rolled out broadly across software and devices, while QKD is added where the highest assurance is needed, such as government or backbone links. IonQ’s advert for a quantum-safe networks architect puts the sequence neatly: inventory your cryptography, make it agile, migrate to post-quantum algorithms, and in the highest-assurance segments add quantum key distribution. Europe’s EuroQCI and Singapore’s national quantum-safe network programme follow a similar logic.
What this means for your career
| Post-quantum cryptography | Quantum key distribution | |
|---|---|---|
| Core background | Mathematics, computer science, cryptography | Physics, optics, electrical engineering |
| Typical work | Algorithm design, secure implementation, formal verification, side-channel protection, migration planning | Optical system design, detectors, electronics and FPGA, security proofs, testing and certification |
| Example roles | Lattice cryptography RA (NUS), applied scientist, AWS crypto libraries | QKD security evaluation (DTU), FPGA developer for a QKD system |
Some of the most interesting jobs sit between the two, for example hardware-security research that evaluates both PQC and QKD in embedded devices, or architecture roles that design how the two fit into real networks. For a wider view of the field, see Quantum Communication in 2026 and our careers guide, or browse current quantum communication jobs.
