What Is Post-Quantum Cryptography?

For decades, modern cybersecurity has relied on cryptographic algorithms such as RSA, ECC, and Diffie-Hellman. These algorithms protect everything from HTTPS connections and VPNs to digital signatures and encrypted messaging.

However, the emergence of large-scale quantum computers threatens the mathematical foundations of these widely used cryptographic systems.

Post-Quantum Cryptography (PQC) is the next generation of cryptography designed to remain secure even against attacks from quantum computers.

In this guide, we'll explain what PQC is, why it matters, and how organizations can start preparing today.

Why Current Cryptography Is at Risk

Most public-key cryptography used today depends on mathematical problems that are extremely difficult for classical computers to solve.

Examples include:

• Integer factorization (RSA)
• Elliptic curve discrete logarithms (ECC)
• Discrete logarithms (Diffie-Hellman)

Even the world's fastest supercomputers would require billions of years to break sufficiently large keys using brute force.

Quantum computers change this assumption.

Using Shor's Algorithm, a sufficiently powerful quantum computer could solve these mathematical problems exponentially faster, making today's public-key cryptography vulnerable.

This means technologies that secure:

• HTTPS
• SSH
• VPNs
• Email encryption
• Blockchain wallets
• Digital certificates
• Software signing

may eventually become insecure.

What Is Post-Quantum Cryptography?

Post-Quantum Cryptography refers to cryptographic algorithms that are designed to withstand attacks from both:

• Classical computers
• Quantum computers

Unlike Quantum Key Distribution (QKD), PQC does not require specialized hardware.

Instead, PQC algorithms can be implemented in software, making them practical for existing applications, cloud infrastructure, APIs, and embedded systems.

Why Does This Matter Today?

Many people assume quantum computers are still decades away.

However, security experts are already preparing because of a threat known as:

Harvest Now, Decrypt Later (HNDL)

Attackers can intercept and store encrypted communications today, then decrypt them once quantum computers become capable enough.

This is especially concerning for data that must remain confidential for many years, including:

• Government records
• Healthcare data
• Financial information
• Intellectual property
• Source code
• Customer databases

If your data needs to stay secure for 10–20 years, quantum-safe migration should begin now.

Which Algorithms Are Vulnerable?

The following public-key algorithms are considered vulnerable to future quantum attacks:

| Algorithm | Status | |-----------|--------| | RSA | ❌ Vulnerable | | ECC | ❌ Vulnerable | | Diffie-Hellman | ❌ Vulnerable | | DSA | ❌ Vulnerable | | ECDSA | ❌ Vulnerable |

It's important to note that symmetric cryptography is affected much less.

Algorithms like:

• AES-256
• SHA-384
• SHA-512

remain relatively secure, although larger key sizes are generally recommended.

The New Generation of Cryptography

After years of international research, the National Institute of Standards and Technology (NIST) standardized several post-quantum algorithms.

ML-KEM

Formerly known as CRYSTALS-Kyber, ML-KEM is designed for:

• Key establishment
• Key exchange
• Encryption

It is expected to replace RSA and Diffie-Hellman in many applications.

ML-DSA

Previously called CRYSTALS-Dilithium, ML-DSA provides:

• Digital signatures
• Software signing
• Certificate signing
• Authentication

It is expected to replace RSA signatures and ECDSA.

SLH-DSA

SLH-DSA (formerly SPHINCS+) is another standardized digital signature algorithm that offers a hash-based alternative for specific security requirements.

Where Is PQC Used?

Post-Quantum Cryptography is expected to secure:

• HTTPS/TLS
• VPN connections
• Cloud infrastructure
• APIs
• Identity providers
• IoT devices
• Enterprise applications
• Software updates
• Code signing
• Blockchain infrastructure

As organizations modernize their security stacks, PQC will become a fundamental requirement.

Challenges of Migration

Migrating to post-quantum cryptography isn't as simple as replacing one library with another.

Organizations often face challenges such as:

• Unknown cryptographic assets
• Hardcoded keys
• Legacy libraries
• Multiple programming languages
• Third-party dependencies
• Outdated TLS configurations
• Hidden cryptographic implementations

Large enterprises may have thousands of repositories containing cryptographic code that has accumulated over many years.

Without visibility into where cryptography is used, planning a migration becomes extremely difficult.

The Importance of Crypto Discovery

Before organizations can migrate to quantum-safe algorithms, they first need to answer questions like:

• Where is RSA used?
• Which applications rely on ECC?
• Are any deprecated algorithms still deployed?
• Which libraries implement cryptography?
• Which repositories contain digital signature logic?

This process is known as cryptographic discovery or crypto inventory.

Automated scanning tools help engineering teams identify cryptographic assets across large codebases, making migration planning significantly easier.

Best Practices for Preparing Today

Even if your organization isn't ready to migrate immediately, there are several practical steps you can take.

Inventory Your Cryptography

Identify every cryptographic algorithm currently used across your applications.

Remove Deprecated Algorithms

Replace outdated technologies such as:

• SHA-1
• MD5
• Weak RSA key sizes

before beginning a PQC migration.

Build Crypto Agility

Design applications so cryptographic algorithms can be replaced without major architectural changes.

Follow NIST Standards

Monitor guidance from NIST and adopt standardized algorithms rather than experimental implementations.

Automate Security Scanning

Use automated code scanning to continuously detect cryptographic algorithms, deprecated implementations, and migration opportunities.

The Future Is Hybrid

Many organizations are expected to adopt hybrid cryptography, combining classical and post-quantum algorithms during the transition period.

This approach provides compatibility with existing systems while introducing protection against future quantum threats.

Hybrid deployments are already appearing in experimental TLS implementations and enterprise security products.

Conclusion

Quantum computing represents one of the biggest shifts in modern cybersecurity.

While practical attacks are not yet possible, organizations cannot afford to wait until quantum computers become a reality.

Preparing today means:

• Understanding where cryptography exists
• Building a complete crypto inventory
• Following NIST standards
• Planning a gradual migration to post-quantum algorithms

Organizations that begin this process early will be better positioned to protect their systems, maintain compliance, and avoid costly emergency migrations in the future.

Frequently Asked Questions

Is Post-Quantum Cryptography available today?

Yes. NIST has standardized multiple post-quantum algorithms, and many vendors are already integrating them into security products.

Will quantum computers break AES?

Not in the same way they threaten RSA or ECC. AES-256 remains considered secure with appropriate key sizes.

Should companies migrate now?

Organizations should begin assessing their cryptographic assets and preparing migration plans today, especially if they protect long-lived sensitive data.

Does PQC require quantum computers?

No. Post-Quantum Cryptography is designed to run on conventional hardware and existing software systems.

What's the first step toward quantum readiness?

The first step is understanding where cryptography exists within your infrastructure. Building a complete cryptographic inventory enables organizations to prioritize migration efforts and reduce future risk.