What Is Post-Quantum Cryptography?
Post-quantum cryptography (PQC), also called quantum-resistant or quantum-safe cryptography, refers to cryptographic algorithms designed to be secure against attacks from both classical computers and quantum computers.
Unlike the cryptographic algorithms we use today (RSA, ECC, Diffie-Hellman), which rely on mathematical problems that quantum computers can solve efficiently, PQC algorithms are built on different mathematical foundations that remain hard for quantum computers to break.
Key Point
Post-quantum cryptography isn't about using quantum computers for encryption. It's about protecting against the threat that quantum computers pose to current encryption methods.
Why Does PQC Matter?
The cryptographic algorithms protecting virtually all digital communication today will become vulnerable when large-scale quantum computers become available. This includes:
- TLS/SSL connections securing websites and online transactions
- VPNs protecting corporate networks
- Digital signatures authenticating software and documents
- Encrypted email and messaging applications
- Cryptocurrency and blockchain technologies
- Government and military communications
The Quantum Threat to Current Cryptography
Today's public-key cryptography relies on two main mathematical problems:
| Problem | Used By | Quantum Vulnerability |
|---|---|---|
| Integer Factorization | RSA | Broken by Shor's Algorithm |
| Discrete Logarithm | Diffie-Hellman, DSA, ECDSA, ECDH | Broken by Shor's Algorithm |
A quantum computer running Shor's algorithm could solve these problems exponentially faster than classical computers. What would take classical computers billions of years could be solved in hours or days on a sufficiently powerful quantum computer.
Harvest Now, Decrypt Later
Adversaries are already collecting encrypted data with the intent to decrypt it once quantum computers become available. Data with long-term sensitivity (health records, classified information, trade secrets) is at risk today.
How Does Post-Quantum Cryptography Work?
PQC algorithms use mathematical problems that are believed to be hard for both classical and quantum computers. The main categories include:
Lattice-Based Cryptography
The most promising and widely adopted approach. These algorithms are based on the difficulty of finding the shortest vector in a high-dimensional lattice. NIST's primary PQC standards (ML-KEM and ML-DSA) are lattice-based.
- Advantages: Fast, relatively small key sizes, well-understood security
- Examples: ML-KEM (CRYSTALS-Kyber), ML-DSA (CRYSTALS-Dilithium)
Hash-Based Signatures
Based on the security of cryptographic hash functions. These have the strongest security proofs but are limited to signatures only.
- Advantages: Conservative security assumptions, minimal attack surface
- Examples: SLH-DSA (SPHINCS+), XMSS, LMS
Code-Based Cryptography
Based on the difficulty of decoding random linear codes. One of the oldest post-quantum approaches, dating back to 1978.
- Advantages: Very fast encryption/decryption
- Disadvantages: Large public keys
Isogeny-Based Cryptography
Based on finding paths between elliptic curves. Offered the smallest key sizes but faced a significant setback when SIDH/SIKE was broken in 2022.
NIST PQC Standards
After a rigorous multi-year evaluation process, NIST finalized its first post-quantum cryptography standards in 2024:
| Standard | Algorithm | Type | Use Case |
|---|---|---|---|
| FIPS 203 | ML-KEM (Kyber) | Key Encapsulation | Key exchange, TLS |
| FIPS 204 | ML-DSA (Dilithium) | Digital Signature | Code signing, certificates |
| FIPS 205 | SLH-DSA (SPHINCS+) | Digital Signature | Backup/conservative choice |
These standards provide organizations with NIST-approved algorithms they can begin integrating into their systems.
The Quantum Threat Timeline
While no one knows exactly when cryptographically relevant quantum computers (CRQCs) will arrive, experts generally estimate:
- Conservative estimates: 2035-2040
- Moderate estimates: 2030-2035
- Aggressive estimates: 2027-2030
However, the timeline for when you need to act is now, because:
- Migration takes years – Large organizations may need 5-10 years to fully transition
- Data longevity – Data encrypted today may need to remain confidential for decades
- Supply chain – Your vendors and partners also need to migrate
- Regulatory requirements – Mandates for quantum-ready security are emerging
How to Get Started with PQC
Organizations should begin preparing for the post-quantum transition now. Here's a high-level roadmap:
1. Inventory Your Cryptography
Identify where cryptography is used in your organization:
- Applications and services
- Network infrastructure
- Data at rest and in transit
- Third-party dependencies
2. Assess Your Risk
Evaluate which systems handle data with long-term confidentiality requirements and prioritize those for early migration.
3. Develop Crypto Agility
Build systems that can easily switch between cryptographic algorithms. This is essential for both the PQC transition and future algorithm updates.
4. Test Hybrid Implementations
Many organizations are deploying "hybrid" approaches that combine classical and post-quantum algorithms during the transition period.
5. Engage Vendors
Work with your technology vendors to understand their PQC roadmaps and ensure alignment with your timeline.
QRAMM Can Help
The Quantum Readiness Assurance Maturity Model (QRAMM) provides a structured framework for assessing your organization's quantum readiness across four dimensions: Cryptographic Visibility, Strategic Governance, Data Protection, and Implementation Readiness.
Conclusion
Post-quantum cryptography represents one of the most significant transitions in the history of information security. While quantum computers capable of breaking today's encryption don't exist yet, the time to prepare is now.
Organizations that start their quantum readiness journey today will be better positioned to protect their data, meet emerging regulatory requirements, and maintain security through the quantum transition.
The QRAMM framework and toolkit provide a practical, structured approach to assessing your current state and developing a roadmap for quantum readiness. Download the toolkit to begin your assessment today.