Store Now, Decrypt Later: The Quantum Computing Threat

Quantum computing technology visualization showing advanced quantum computer

What is Harvest-Now-Decrypt-Later (HNDL)?

Harvest-Now-Decrypt-Later (HNDL) is the practice of collecting encrypted data today with the intent to decrypt it in the future—for example, once large-scale quantum computers or new cryptanalytic breakthroughs become available. Long-lived secrets (contracts, mission data, health records) and regulated workloads face elevated risk because the confidentiality window extends for years or decades.

Attackers don’t have to break encryption now—they can exfiltrate ciphertext and wait. If a scheme weakens later, previously harvested data becomes readable. This is particularly critical for governments, defense supply chains, financial institutions, and enterprises with compliance retention requirements.

Why HNDL Matters Now

The threat timeline has compressed. While large-scale quantum computers capable of breaking RSA-2048 or ECC P-256 don’t exist today, projections suggest viable attacks within 10-15 years. Data encrypted today with classical algorithms may become vulnerable within the retention period of:

Healthcare records: 7-25 years (HIPAA, regional laws)
Government classified data: 25-75 years
Financial transactions: 7-10 years (compliance)
Legal contracts: 5-20 years

Organizations that delay migration risk exposing sensitive data that was encrypted years before quantum capability emerged. The window to act is shrinking.

How to Mitigate HNDL Risk

1. Adopt Post-Quantum Cryptography (PQC) Now

NIST has standardized three post-quantum algorithms:

ML-KEM (CRYSTALS-Kyber): Lattice-based key encapsulation
ML-DSA (CRYSTALS-Dilithium): Lattice-based signatures
SLH-DSA (SPHINCS+): Hash-based signatures

Begin phased rollout to key exchange mechanisms immediately. Hybrid approaches (classical + PQ) provide backward compatibility during transition.

2. Prefer Independent Algorithm Families

Relying on a single PQ family (e.g., only lattice-based) creates correlated failure risk. If a breakthrough weakens lattices, all your encrypted data is exposed. Defense-in-depth requires combining independent families:

Lattice-based: CRYSTALS-Kyber (ML-KEM)
Code-based: Classic McEliece

Dual-layer composition raises the cost of future decryption even if a single family degrades.

3. Strengthen Identity, Rotation, and Policy Controls

PQ algorithms alone aren’t sufficient. Organizations must:

Enforce strong identity and authentication (MFA, hardware tokens)
Rotate keys regularly (quarterly for high-value data)
Apply least-privilege access policies
Enable audit logging and anomaly detection

Cellcrypt’s Dual-Layer Post-Quantum Design

Cellcrypt implements a dual-layer PQ architecture that composes:

CRYSTALS-Kyber (ML-KEM): NIST-standardized lattice-based KEM
Classic McEliece: Code-based KEM with decades of cryptanalytic confidence

This composition sits atop modern end-to-end encryption, strong identity, and policy controls. The result:

Defense-in-depth against correlated algorithm failure
Backward compatibility with existing deployments
Compliance-ready audit trails and retention controls
Protection for voice, messaging, and file transfer

Learn more: How Cellcrypt’s dual-layer PQ encryption works

Implementation Timeline

Phase 1: Assessment (Months 1-2)

Inventory current encryption usage (TLS, VPN, messaging, storage)
Identify long-lived secrets and retention policies
Map dependencies on classical algorithms (RSA, ECC)

Phase 2: Hybrid Rollout (Months 3-6)

Deploy hybrid (classical + PQ) key exchange for TLS and messaging
Test performance impact on production-like workloads
Update client libraries and SDKs

Phase 3: Full PQ Migration (Months 7-12)

Migrate to PQ-only or dual-layer PQ for high-value data
Deprecate classical-only modes
Conduct third-party security audit

Frequently Asked Questions

What is HNDL?

Collecting encrypted data now to decrypt later, e.g., with future quantum capabilities or cryptanalytic advances.

How does Cellcrypt mitigate HNDL?

By combining two independent post-quantum families (CRYSTALS-Kyber + Classic McEliece) alongside modern E2EE and policy controls. This dual-layer approach ensures that even if one family is compromised, the other remains secure.

Should organizations migrate now?

Yes. If your data must remain confidential for years, you should begin phased PQ rollout and policy updates immediately. Delaying migration increases the risk that harvested data will become readable within your retention window.

What about performance?

CRYSTALS-Kyber is highly efficient (sub-millisecond operations). Classic McEliece has larger keys but is suitable for key establishment. In practice, dual-layer overhead is negligible for voice, messaging, and file transfer.

Is hybrid (classical + PQ) enough?

Hybrid is a good first step for backward compatibility, but dual-PQ (two independent PQ families) provides stronger defense-in-depth against correlated failure.