It is tempting to think quantum risk is a problem for the future. But for some data, the risk has already begun, because encrypted information can be stolen now and read later.
How the attack works
Encrypted internet traffic can be copied as it travels. Without the key, the copy is useless scrambled data, for now. In a “harvest now, decrypt later” attack, someone stores that data and waits until a quantum computer can recover the key.
The attacker doesn’t need a quantum computer today, just storage and patience. Storage keeps getting cheaper, so keeping large amounts of intercepted data for years is realistic for well-funded groups.
Who is warning about it
This is not a fringe idea. In August 2023, the US Cybersecurity and Infrastructure Security Agency (CISA), the National Security Agency (NSA) and NIST jointly warned that adversaries could be collecting encrypted data now to decrypt it once quantum computers mature. Security agencies in the UK, the EU and elsewhere give similar advice.
Which data is most at risk
The key question is how long your data needs to stay secret.
- ◆Short-lived data, such as a one-time login code, loses its value within minutes and is low risk.
- ◆Long-lived data, such as health records, legal documents, trade secrets, government files and identity data, may still be sensitive in 10, 20 or 50 years.
- ◆Keys and passwords captured today could unlock other systems later if they are still in use.
Mosca’s rule: a simple test
Canadian researcher Michele Mosca suggested a simple way to think about the risk. Add up two numbers:
- ◆X: how many years your data must stay secret.
- ◆Y: how many years it will take you to upgrade your systems to quantum-safe encryption.
Then compare the total with Z, the number of years until a quantum computer can break today’s encryption. If X + Y is greater than Z, you already have a problem, because data sent today will still matter when it can be unlocked.
What actually helps
The main defence is to stop protecting long-lived secrets with quantum-vulnerable key exchange. Switching to hybrid key exchange that includes ML-KEM, the NIST standard published in 2024, protects new traffic from being harvested. Data that has already been captured cannot be protected after the fact, which is why starting early matters.
task_altKey takeaways
- check_circleEncrypted data can be recorded now and decrypted once quantum computers are ready.
- check_circleUS agencies, including CISA, the NSA and NIST, have publicly warned about this threat.
- check_circleMosca’s rule: if secrecy time plus upgrade time exceeds time to a quantum computer, act now.
- check_circleQuantum-safe key exchange protects new traffic; recorded traffic can’t be fixed later.