Harvest-Now-Decrypt-Later: Quantum Crypto Risk Timeline

Threat Timeline

Data shelf-life X 15 yr

PQC migration time Y 5 yr

Years to Q-day Z 10 yr

Playback speed 1.0×

Mosca Risk Verdict

—

X + Y vs Z

Live Readouts

Elapsed year

0.0 / 10

Packets harvested

Exposed at Q-day

PQC-safe packets

Legend

RSA/ECC — vulnerable, still stored PQC-protected — quantum-safe Exposed the moment Q-day hits Expired before Q-day — no longer sensitive

How it works

An adversary doesn't need a quantum computer today to threaten today's traffic — they only need a hard drive. This is the "harvest now, decrypt later" attack: intercept and store RSA/ECC-encrypted data now, then decrypt it retroactively once a cryptographically-relevant quantum computer exists.

Mosca's theorem gives the exact condition for risk. Let:

X = shelf-life  — years the data must stay confidential
Y = migration   — years needed to deploy post-quantum crypto
Z = Q-day       — years until a quantum computer can break it

Risk exists if:  X + Y  >  Z

Every packet spawned here is timestamped with its own harvest year. Its secrecy deadline is harvestYear + X. Packets minted before migration completes (year Y) carry classical RSA/ECC keys; once migration finishes, new packets carry post-quantum keys (ML-KEM/Kyber-class lattice problems) and are immune to Shor's algorithm regardless of Q-day. When the simulated clock reaches Z, every still-classical packet whose secrecy deadline hasn't passed is flagged exposed — visualized as a red flash in the vault.

The real numbers are sobering: Gidney & Ekerå (2019) estimate ~20 million noisy physical qubits and about 8 hours of runtime to factor a 2048-bit RSA key with Shor's algorithm — a resource level well beyond today's processors but not beyond a multi-decade roadmap. NIST finalized its post-quantum standards (ML-KEM for key exchange, ML-DSA for signatures) in 2024 precisely so organizations can start the migration clock (Y) before Q-day (Z) arrives, which is the only lever this simulation lets you actually control.

Harvesting…

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