Harvest Now, Decrypt Later: Why Your Encrypted Data Is Already at Risk
Adversaries are collecting encrypted data today, banking on future quantum computers to break it. If your organisation holds long-lived sensitive records, the threat is not theoretical — it is already in motion.
The harvest-now-decrypt-later (HNDL) attack strategy is straightforward: a threat actor intercepts and stores encrypted data today, then waits until a cryptographically relevant quantum computer (CRQC) is available to decrypt it. The data is useless to them now, but it will not always be.
For most organisations, this sounds like a distant problem. It is not. Intelligence agencies, nation-state actors, and well-resourced criminal groups are already harvesting encrypted traffic at scale. The question is not whether your data has been collected — it is whether it will still be sensitive when quantum decryption becomes feasible.
The critical variable is data shelf life. A payment transaction processed today has a shelf life of hours. A patient's genomic record, a government treaty, a long-term financial contract, or a classified intelligence report may remain sensitive for decades. Any data that must remain confidential beyond the expected arrival of a CRQC — broadly estimated between 2030 and 2035 by NIST and national cybersecurity agencies — is already at risk.
NIST's post-quantum cryptography standards, finalised in 2024, provide the algorithmic foundation for defence: ML-KEM (CRYSTALS-Kyber) for key encapsulation, ML-DSA (CRYSTALS-Dilithium) and SLH-DSA (SPHINCS+) for digital signatures. But algorithm selection is only one part of the challenge. Organisations must first understand which of their cryptographic assets protect long-lived data, and in what order those assets should be migrated.
A Cryptographic Bill of Materials (CBOM) is the starting point. By cataloguing every algorithm, certificate, key, and protocol in use — and tagging each with the data it protects and its estimated shelf life — organisations can calculate a harvest-now-decrypt-later exposure score and prioritise migration accordingly.
The organisations most exposed are those that have not yet begun this inventory. The organisations best positioned are those that have already mapped their cryptographic estate, identified their highest-risk assets, and started the migration planning process. The window to act before quantum decryption becomes feasible is measured in years, not decades.