Harvest Now, Decrypt Later.

An attack strategy where adversaries record encrypted traffic today to decrypt it once cryptographically relevant quantum computers become available. It belongs to the Cryptography category of cybersecurity.

An attack strategy where adversaries record encrypted traffic today to decrypt it once cryptographically relevant quantum computers become available.

Harvest now, decrypt later (HNDL), also called store-now-decrypt-later, describes adversaries who intercept and archive encrypted communications today with the expectation that future cryptographically relevant quantum computers will break the underlying public-key schemes, especially RSA and elliptic-curve Diffie-Hellman. The threat is most acute for long-lived secrets such as state-level intelligence, healthcare records, intellectual property, and root cryptographic keys whose value persists for decades. Mitigations focus on migrating to NIST-selected post-quantum algorithms (ML-KEM, ML-DSA, SLH-DSA), hybrid TLS and IPsec key exchange, shortening secret lifetimes, and enforcing crypto agility so algorithms can be replaced without redesign.

Defences for Harvest Now, Decrypt Later typically combine technical controls and operational practices, as detailed in the full definition above.

Common alternative names include: HNDL, Store now, decrypt later.