Quantum computing poses an imminent cryptographic threat through 'Harvest Now, Decrypt Later' (HNDL) attacks, where state-sponsored actors collect encrypted data today to decrypt once cryptographically relevant quantum computers (CRQCs) arrive. Four key risks are outlined: breaking public-key encryption (RSA, ECC, Diffie-Hellman), HNDL data interception, Grover's algorithm accelerating brute-force attacks, and AI-quantum convergence amplifying vulnerability discovery. NIST's 2024 PQC standards and US/EU regulatory mandates are accelerating post-quantum migration timelines. Organizations are advised to complete cryptographic inventories by 2026, design for crypto-agility by 2028, and prioritize migration of long-lived sensitive data and identity infrastructure. Delaying preparation risks compressed timelines, higher costs, and regulatory exposure.
