Harvest Now, Decrypt Later Explained
CyberRank Research
Harvest now, decrypt later (HNDL) is an attack strategy in which an adversary records encrypted traffic today and stores it until a future quantum computer can break the key exchange that protected it. It turns tomorrow's quantum risk into a present-day confidentiality risk for any data that must stay secret for years. CyberRank's quantum-crypto exposure check (Beta) shows which of your vendors' public TLS and SSH services still use only quantum-vulnerable key exchange.
TL;DR
- HNDL means encrypted traffic recorded today can be decrypted once a cryptographically relevant quantum computer exists.
- The risk depends on how long data must stay confidential: health, banking, identity, legal and government data are most exposed.
- Key exchange is the priority, because recorded key exchange can be broken retroactively; forged signatures only matter later.
- CyberRank checks vendors' public key exchange separately from certificate signatures (Beta), so you see who already protects traffic against HNDL.
What is harvest now, decrypt later?
An attacker copies encrypted traffic or files now, keeps them, and decrypts them once a quantum computer can break the public-key key exchange used at the time.
Today's TLS and SSH sessions usually agree a key with RSA, Diffie-Hellman or elliptic-curve algorithms. A sufficiently large quantum computer running Shor's algorithm would break these. The session data itself is protected with symmetric encryption such as AES, which quantum computers only weaken, but whoever recovers the agreed key can read everything.
This is why HNDL is the main reason to act before a quantum computer exists, as explained in our article about quantum security and post-quantum cryptography.
Which data is most at risk?
Data that must stay confidential beyond about 2030, because that is roughly the horizon NIST uses for retiring quantum-vulnerable algorithms.
Short-lived data, such as a one-time session token, matters much less. Rank systems and vendors by how long their data must stay secret, not only by how sensitive it is today. Much of that traffic crosses your vendors' attack surface, not yours.
- Health records and insurance data.
- Banking, payment and identity data.
- Contracts, legal files and intellectual property.
- Government and state information.
How do you reduce HNDL exposure?
Move key exchange to post-quantum or hybrid algorithms first, starting with services that carry long-life data, and ask your vendors to do the same.
- Find where long-life data travels, including through vendors.
- Prefer hybrid key exchange, such as X25519 combined with ML-KEM-768, which NIST accommodates during the transition.
- Ask critical vendors when key exchange on services carrying your data will be quantum-safe, and put the date in the contract.
- Re-check regularly, because servers and libraries change.
How CyberRank helps
CyberRank's quantum-crypto exposure check (Beta) looks at the public TLS and SSH services of each vendor, separates key exchange from certificate signatures, and gives a not, partly or fully quantum-safe posture. That tells you which vendors still expose traffic to HNDL today. CyberRank sees only internet-facing services; it cannot inspect a vendor's internal systems or backups.
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