Harvest Now, Decrypt Later is a simple attack. An adversary records encrypted traffic today, stores it, and decrypts it once quantum computers can break the public-key cryptography that protected it.
The attack needs no breach of your network. It needs only a copy of your traffic in transit, and patience.
For most commercial data, the exposure is limited: the information expires before the decryption capability arrives. Critical infrastructure is different. SCADA topologies, patient records, defense communications and inter-bank flows stay sensitive for decades. Traffic recorded in 2026 that becomes readable in 2031 is still a live loss.
This is why regulators have stopped treating quantum risk as a future problem. The US, EU, KSA and France have all set procurement deadlines that require quantum-safe protection years before a cryptographically relevant quantum computer is expected.
The defence is to make the recorded ciphertext worthless: wrap traffic in NIST-standardised post-quantum encryption now, so that what an adversary stores today stays computationally infeasible to decrypt later. That is what Tessera does, beside the network you already run.