Harvest-now, decrypt-later is a threat model in which an attacker records encrypted traffic or stolen encrypted files today and keeps them for future decryption. The idea is simple: even if current encryption is strong, the data may be exposed later if better cryptanalysis, compromised keys, or quantum computing make the ciphertext easier to break.
This matters most for information that must remain secret for many years, such as identity data, intellectual property, legal records, and government communications. In real attacks, adversaries may quietly collect VPN sessions, email archives, backups, or intercepted network traffic without trying to decrypt them immediately. Defenders reduce the risk by using modern cryptography, protecting key material, shortening data retention, enabling perfect forward secrecy, and planning for post-quantum migration. The key question is not only whether data is safe today, but whether it will still be safe when attackers revisit it later.