Quantum Threats to Existing Systems

The quantum threat to existing systems is not a future problem — it is an active concern today. The 'Harvest Now, Decrypt Later' (HNDL) strategy means that nation-state adversaries and sophisticated attackers are already intercepting and storing encrypted communications with the expectation of decrypting them once a cryptographically relevant quantum computer (CRQC) becomes available. Any data with a secrecy requirement lasting beyond the expected arrival of a CRQC is at risk right now.

Public Key Infrastructure (PKI) is particularly vulnerable because it underpins certificate chains, code signing, secure boot, TLS connections, and identity verification. A quantum computer capable of running Shor's algorithm would compromise the trust anchors of the entire internet. Protocol vulnerabilities extend beyond just the cryptographic primitives — key exchange mechanisms in TLS, IPsec, SSH, and S/MIME all rely on algorithms that Shor's algorithm can break.

Critical infrastructure sectors — energy, financial services, healthcare, defense, and telecommunications — face the highest risk because their systems have long operational lifetimes, handle data with decades-long sensitivity, and are difficult to upgrade. The intersection of legacy systems, supply chain complexity, and the quantum timeline creates a challenge that requires strategic planning starting now, not when quantum computers arrive.