Harvest Now, Decrypt Later
Also known as: HNDL, Store Now, Decrypt Later
Definition
A threat model in which an adversary records currently-unbreakable encrypted data traffic today, storing it in anticipation of decrypting it retroactively once a cryptographically relevant quantum computer becomes available, making data confidentiality duration a relevant risk factor independent of current cryptographic strength.
Key Points
- Requires no current quantum computing capability to execute — an adversary simply records encrypted traffic now and stores it, deferring the decryption attempt until quantum computing capability catches up
- Makes data confidentiality duration, not just current cryptographic strength, the relevant risk factor — data that must remain confidential for decades is exposed to this threat even though current encryption is completely secure against any classical or existing quantum attack today
- Reframes quantum-safe migration urgency independent of exactly when a cryptographically relevant quantum computer will actually exist, since the recording (harvesting) can happen today regardless of how far off the decryption capability remains
- Most directly relevant to data with long confidentiality requirements — government and defense communications, long-lived critical infrastructure configuration, and similar data whose sensitivity persists for years or decades
- Directly addressed by migrating to post-quantum cryptography or quantum key distribution today, since data encrypted with quantum-safe methods from the outset cannot be harvested for future decryption in the same way
Concept
An adversary executing this threat model doesn't need any quantum computing capability today — they simply intercept and store encrypted traffic now, betting that at some future point, a sufficiently capable quantum computer running an algorithm like Shor's algorithm will let them decrypt what they've recorded. This means the actual moment of risk realization is decoupled from the moment of data exposure: the data is captured today, but the confidentiality breach — if it happens at all — occurs whenever quantum decryption capability eventually matures, however far in the future that turns out to be.
Explainer
The strategic reframing HNDL forces is that migration urgency should be driven by how long data must remain confidential, not by how soon quantum computers are expected to become cryptographically relevant — an organization holding data that must stay confidential for thirty years faces real HNDL risk today even if credible quantum computing timelines suggest decades before decryption capability exists, because the recording can happen now and the clock on that data's required confidentiality period is already running regardless of when the threat materializes. This is precisely why quantum-safe migration planning for genuinely long-lifetime sensitive data is treated as a present-day action rather than something to defer until quantum computing capability is more imminent — waiting for more certainty about quantum computing timelines doesn't protect data an adversary may already be harvesting today. For CE verticals, HNDL risk is concentrated in exactly the kind of long-lifetime sensitive data this corpus's quantum security material has already identified — government and defense communications, and critical energy or industrial configuration data whose sensitivity doesn't expire quickly — making migration planning for that specific data category a genuine near-term priority independent of broader uncertainty about quantum computing's eventual timeline.
Cite this entry
Harvest Now, Decrypt Later. ConnectedEarth Knowledge Base. https://connectedearth.space/knowledge-base/harvest-now-decrypt-later/ (updated 13 September 2026).