Harvest now, decrypt later: the business risk

Why the lifetime of information matters

Harvest now, decrypt later (HNDL) describes an adversary collecting encrypted information now in the hope of recovering it later. Where protection depends on quantum-vulnerable public-key cryptography, a future capable quantum computer could change the confidentiality risk.

Separate three questions

How long must the information remain confidential? How could an adversary obtain the encrypted material? How long will it take to change the systems and suppliers protecting it? Answering these together is more useful than guessing a single Q-Day date.

Build an exposure view

Start with information categories, not secret contents. Record the required protection lifetime, the business owner, the services that store or transmit it and the relevant trust dependencies. Include backups, outsourced processing and cross-organisation exchange.

For example, a hypothetical engineering design may remain valuable after the service that originally transmitted it is replaced. Changing a future connection does not automatically protect a copy already collected.

Choose proportionate next steps

Prioritise evidence collection where long confidentiality lifetimes meet plausible exposure and slow replacement cycles. Consider data minimisation, retention decisions and access controls alongside the cryptographic transition. These controls reduce exposure but should not be presented as substitutes for appropriate cryptography.

Continue exploring

• PQCEMM: enterprise post-quantum maturity
• Q-Day and quantum risk planning
• Cryptographic discovery and inventory

Primary sources

• NCSC migration timelines