Post quantum cryptography, quantum key distribution and pre-shared keys are three routes to quantum-resistant data in transit. Learn about their pros and cons.
Quantum computers threaten the two encryption methods differently
Every encrypted link does two jobs: agreeing on a secret key (key exchange, or KEX) and locking the data with it. The first usually relies on asymmetric cryptography, the second on symmetric.
Most secure connections use both. But which one is under more serious threat?
Symmetric encryption
One shared key, for example AES. Like a house key where the same key locks and unlocks. Both ends need an identical copy. It is fast, so it protects the actual data flowing over the link.
Asymmetric encryption
Like an open padlock you can hand to anyone: they snap it shut, only you hold the key that opens it. It lets two parties agree on a secret key over an open network, and prove who they are.
Quantum impact: weakened, easy to fix
A quantum computer can speed up guessing the key, roughly halving its strength. Long keys such as AES-256 still leave a huge safety margin, so adding key length makes this method safer.
Quantum impact: broken outright
A large quantum computer can work out the private key from the public one. Longer keys don't help. The maths itself has to be replaced..
Why it matters now
the weak point is the moment two sites agree on their key. An attacker who records that exchange today can unlock the key, and everything it protected, once a quantum computer is available.
Three ways to make the key exchange quantum safe
Each one tackles the broken asymmetric step in a different way.
New public-key algorithms built on problems quantum computers can't shortcut, such as ML-KEM. It runs as software on ordinary hardware. Hybrid mode uses old and new together, so the connection stays safe if either holds.
Use physics instead Quantum key distribution
Sends key material as single particles of light over a dedicated fibre or satellite link. Eavesdropping disturbs them and can be noticed. It needs special hardware and still relies on normal cryptography to confirm who is on the other end.
Skip the exchange Pre-shared keys
Installs the same long symmetric key at both ends in advance, so no public-key step is needed. Simple for a few links, but every key has to be created, delivered and replaced by hand.
Quantum-safe describes different methods and products
The three methods become quantum safe are post quantum cryptography (PQC), quantum key distribution (QKD) and pre-shared keys. Each means something very different of your network, your budget and your team.
1. Same label with different foundations
PQC is software based and rests on maths problems quantum computers can't shortcut. QKD relies on physics but still needs classical or PQC authentication. Pre-shared keys rest on keeping static secrets secret with manual configurations.
2. The real cost comes after go-live
Purchase price is the small part. Key distribution, rotation, relay sites, audits and algorithm upgrades decide what you pay over five to ten years, and how that grows as you add sites.
3. Regulators have already chosen
NSA, BSI and ANSSI point to post-quantum cryptography as the primary route. The EU roadmap asks organizations to start the transition by 2026 and protect high-risk systems by 2030.
4. Today's traffic is already exposed
Data recorded now can be decrypted once quantum computers mature. Picking an approach you can actually roll out this year protects more than a perfect one that takes years to build.
Maintenance at scale per approach
Add sites and watch what each methods asks of your network and your people.
Scorecard
Directional ratings for a multi-site enterprise or critical-infrastructure network. More filled dots is better.
Criterion
PQChybrid, NQX
QKDquantum keys
PSKpre-shared
Cost to deployHardware, links, installation
Cost to maintainStaff time, infrastructure upkeep
Operational simplicityMoving parts to run and audit
Effort to roll outTime from decision to protected links
Future-proofnessAbility to absorb new threats and standards
ScalabilityAdding sites, distance and bandwidth
Agency backingNSA, NCSC, BSI, ANSSI positions
More filled dots is better. Directional ratings for a multi-site enterprise or critical-infrastructure network; actual results depend on size, topology and existing infrastructure.
Pros and cons
What each approach gets right, and what it costs you.
Post-quantum cryptography
Recommended · hybrid PQC, as in NQX
Pros
Runs on standard hardware over any IP or Ethernet network, at any distance
Keys are negotiated and rotated automatically, with forward secrecy
Hybrid mode keeps classical protection if one algorithm is ever broken
NIST-standardised (FIPS 203) and backed by NSA, NCSC, BSI and ANSSI
Crypto-agile: new algorithms arrive as a software update
Cons
Security rests on maths problems, so algorithms need ongoing lifecycle management
Fixed-function hardware can't be upgraded, so the platform choice matters
Quantum key distribution
Niche · physics-based key exchange
Pros
Key exchange security grounded in physics, not computational hardness
Eavesdropping on the quantum channel is detectable in principle
Cons
Dedicated fibre or satellite links, point to point, roughly 100 km per hop
Longer routes need trusted relay nodes, each a new place to attack
Still needs classical or PQC authentication, so it doesn't replace PQC
Highest capital and running cost; hard to certify; DoS-sensitive
NSA, NCSC, BSI and ANSSI do not recommend it as a primary control
Pre-shared keys
Interim · static symmetric secrets
Pros
Symmetric keys (AES-256) resist known quantum attacks
Cheap and quick for two or three fixed links
Standardised as a stop-gap for IPsec (RFC 8784)
Cons
One secret per pair of sites: the count grows with the square of the sites
Manual out-of-band distribution, rotation and revocation
No forward secrecy: one leaked key exposes all recorded traffic
Human error and stale keys become the real attack surface
The bottom line
QKD adds a physical network you have to buy, protect and certify, and still needs PQC to authenticate it. Pre-shared keys move the problem onto your operations team. Hybrid PQC is the only one of the three that scales across a real network today. NQX runs it at wire speed, up to 100 Gbps at Layer 2 and Layer 3, with automated key management and new algorithms delivered by software.
