Quantum computing and cybersecurity: Why classical cryptography won’t protect tomorrow’s data

For decades, modern cybersecurity has relied on a simple assumption: the mathematical problems protecting our data are too difficult for today’s computers to solve within a practical timeframe.

That assumption has served us remarkably well.

Public key cryptography (PKC), including RSA and Elliptic Curve Cryptography (ECC), secures almost every aspect of our digital lives. Whether you’re accessing online banking, signing software, connecting to a VPN or securing cloud applications, these cryptographic systems provide the trust that enables digital business.

But quantum computing changes the equation.

Unlike classical computers, quantum computers can solve certain mathematical problems in fundamentally different ways. While large-scale, fault-tolerant quantum computers capable of breaking today’s encryption do not yet exist, governments, standards bodies and cybersecurity experts agree that organizations cannot afford to wait until they do.

The era of quantum-safe cybersecurity has already begun.

In August 2024, the US National Institute of Standards and Technology (NIST) published the world’s first finalized post-quantum cryptography (PQC) standards. Around the same time, the UK’s National Cyber Security Centre (NCSC) released guidance encouraging organizations to begin planning their migration now, recognizing that replacing cryptography across large organizations will take many years.

These developments reflect an important shift in thinking.

Quantum computing cybersecurity is no longer about predicting when quantum computers will arrive. It’s about ensuring today’s systems remain secure throughout tomorrow’s technological landscape.

Why quantum computing changes cyber security

Quantum computing is often described as the next major leap in computing power, but the reality is more nuanced.

Quantum computers are not simply faster versions of today’s machines. Instead, they use quantum mechanical properties, including superposition and entanglement, to process certain types of calculations far more efficiently than classical computers.

This distinction matters because many cryptographic systems rely on mathematical problems that are extremely difficult for classical computers to solve.

For example:

  • RSA relies on the difficulty of factoring very large integers.
  • Elliptic Curve Cryptography (ECC) depends on solving discrete logarithm problems over elliptic curves.
  • Diffie-Hellman key exchange also relies on discrete logarithm problems.

For classical computers, solving these problems at cryptographically relevant sizes would take an impractical amount of time.

Quantum computers change that.

Using Shor’s algorithm, a sufficiently capable quantum computer could solve both integer factorization and discrete logarithm problems exponentially more efficiently than classical machines, rendering many of today’s public key cryptographic systems (PKC) insecure.

It is important to understand that not all encryption is equally affected.

Symmetric cryptography, including the Advanced Encryption Standard (AES), is considered significantly more resilient to quantum attacks. Grover’s algorithm offers a theoretical speed-up against symmetric encryption, but its impact is much smaller than Shor’s algorithm. In practice, increasing symmetric key sizes (AES-128 to AES-256) is generally considered an effective mitigation.

The greatest challenge lies with PKC, because it underpins authentication, digital signatures and secure key exchange across virtually every digital ecosystem.

Where classical cryptography is used today

Many people associate encryption with secure messaging or online shopping, but PKC plays a much broader role in modern technology.

It supports trust across almost every connected system, including:

  • Secure web browsing using HTTPS and Transport Layer Security (TLS)
  • Virtual Private Networks (VPNs)
  • Digital certificates and Public Key Infrastructure (PKI)
  • Software and firmware signing
  • Secure software updates
  • Cloud identity and authentication
  • Mobile applications
  • Automotive systems
  • Industrial control systems
  • Medical devices
  • Connected IoT products

In many cases, these systems are deeply embedded within products that remain in service for decades.

Replacing cryptography across these environments is rarely as simple as installing a software update. Organizations often need to assess hardware compatibility, software dependencies, compliance requirements and operational risks before introducing new cryptographic algorithms.

That is why cybersecurity experts increasingly emphasize planning rather than reacting.

The timeline is shorter than many organizations realize

One of the most common misconceptions about quantum-safe cybersecurity is that organizations can simply wait until practical quantum computers become available before taking action.

Unfortunately, cryptography doesn’t work that way.

Sensitive information often needs to remain confidential for many years.

Examples include:

  • Government records
  • Defense communications
  • Healthcare information
  • Intellectual property
  • Financial records
  • Critical infrastructure designs
  • Product development data
  • Customer identities

An engineering design protected today may still hold commercial value 15 years from now.

Medical records may need to remain confidential for decades.

National security information often has even longer protection requirements.

This creates a significant challenge because attackers do not need quantum computers today to exploit future vulnerabilities.

The “harvest now, decrypt later” threat

One of the biggest drivers behind the move to PQC is the growing concern around “harvest now, decrypt later” (HNDL) attacks.

The concept is straightforward.

Rather than attempting to decrypt encrypted information immediately, attackers can:

  1. Intercept encrypted communications today.
  2. Store that encrypted data for years.
  3. Wait until sufficiently capable quantum computers become available.
  4. Decrypt the archived information in the future.

For data with a long confidentiality lifetime, the damage could occur many years after the original information was transmitted.

This risk is no longer viewed as hypothetical.

NIST, the NCSC and the European Union Agency for Cybersecurity (ENISA) have all highlighted the importance of beginning migration planning now because of the long lead times involved in replacing cryptographic infrastructure across large organizations.

Migration is not simply about introducing new algorithms.

Organizations first need to understand where cryptography exists across their systems, which applications depend on vulnerable algorithms and how new quantum-resistant solutions can be integrated without disrupting existing services.

For large enterprises, this discovery process alone can take several years.

When combined with testing, certification, software development and hardware refresh cycles, the overall migration effort can extend well into the next decade.

That is precisely why leading cybersecurity agencies have shifted their messaging from “prepare for quantum computing” to “start preparing now.”

The organizations that begin planning today will have far greater flexibility than those forced into rushed migrations later.

The global response has already started

The transition to quantum-safe security is no longer a theoretical exercise. Governments, standards bodies and technology providers around the world have already begun preparing for the post-quantum era.

One of the biggest milestones came in August 2024, when the National Institute of Standards and Technology (NIST) published its first three finalized PQC standards:

  • FIPS 203: Module-Lattice-Based Key Encapsulation Mechanism (ML-KEM)
  • FIPS 204: Module-Lattice-Based Digital Signature Algorithm (ML-DSA)
  • FIPS 205: Stateless Hash-Based Digital Signature Algorithm (SLH-DSA)

These standards represent years of international collaboration and cryptographic analysis, providing organizations with trusted algorithms for quantum-resistant encryption and digital signatures. With further standardized algorithms on the way, the industry is now actively moving into the hardware and software deployment phase, ensuring these algorithms are standard in practice as well as in documentation.

The UK’s National Cyber Security Centre (NCSC) has also emphasized that migration should begin now, rather than waiting for quantum computers to become a practical threat. Its migration roadmap encourages organizations to identify vulnerable cryptographic systems, prioritize critical assets and build cryptographic agility over the coming years.

Similarly, the European Union Agency for Cybersecurity (ENISA) has highlighted that organizations should begin planning for post-quantum migration well in advance, recognizing that transitioning large, complex infrastructures will take considerable time.

These recommendations all point to the same conclusion: organizations should treat quantum-safe migration as a long-term modernization program rather than an emergency response.

Migration is more complex than replacing algorithms

If quantum-safe migration involved simply swapping RSA for a post-quantum alternative, the transition would already be well underway.

In reality, cryptography is deeply embedded throughout modern technology.

A single organization may rely on hundreds, or even thousands, of cryptographic implementations across:

  • Business applications
  • Cloud platforms
  • Identity management systems
  • Secure communications
  • Mobile applications
  • Connected devices
  • Industrial equipment
  • Software development pipelines
  • Hardware security modules
  • Third-party software and services

Many organizations don’t have a complete inventory of where cryptography is used across their environment.

Without this visibility, replacing vulnerable algorithms becomes significantly more challenging.

This is why many security teams begin by carrying out cryptographic discovery, identifying:

  • Which cryptographic algorithms are currently deployed
  • Where certificates are used
  • Which systems rely on RSA or ECC
  • Which assets require long-term confidentiality
  • Which vendors and suppliers need to support quantum-safe technologies

Only once this inventory has been established can organizations develop an effective migration strategy.

Why cryptographic agility is becoming a business requirement

One of the most important lessons from previous cryptographic transitions is that no algorithm lasts forever.

Over time, new attacks emerge, standards evolve and implementation guidance improves.

Rather than designing systems around a single algorithm, organizations should build cryptographic agility into their infrastructure.

Cryptographic agility is the ability to replace or update cryptographic algorithms with minimal disruption to applications, devices and services.

This flexibility offers several advantages.

Organizations can:

  • Adopt new standards more quickly.
  • Respond to emerging vulnerabilities.
  • Reduce future migration costs.
  • Support hybrid cryptographic deployments.
  • Extend the lifespan of critical systems.

Just as importantly, cryptographic agility reduces the risk of another large-scale migration in the future.

As quantum computing continues to evolve, organizations with agile cryptographic architectures will be far better positioned to adapt than those relying on rigid, hard-coded implementations.

Quantum computing cyber security is about more than encryption

Encryption often dominates discussions around quantum risk, but PKC underpins much more than confidential communications.

Organizations should consider how quantum computing could affect:

Identity and authentication

Digital certificates, identity verification and Public Key Infrastructure (PKI) all depend heavily on PKC. If these systems become vulnerable, trust across digital ecosystems could be undermined.

Software integrity

Digital signatures are used to verify software authenticity and protect firmware updates from tampering. As organizations increasingly rely on over-the-air updates for connected devices, ensuring the integrity of these signatures becomes even more important.

Connected Devices

Automotive platforms, industrial IoT systems, medical devices and semiconductors often have operational lifetimes measured in decades.

These products may remain in service long after today’s cryptographic standards have changed. Planning for future algorithm updates during product design can significantly reduce long-term risk.

Critical Infrastructure

Energy networks, telecommunications providers, transportation systems and financial services all depend on trusted cryptographic communications. For many of these sectors, resilience is just as important as security.

A carefully planned migration helps reduce operational disruption while maintaining trust throughout the transition.

What organizations should do today

Although the exact timeline for cryptographically relevant quantum computers remains uncertain, organizations do not need to wait for complete certainty before taking practical action.

Most experts recommend beginning with a structured, phased approach.

1. Understand your cryptographic landscape

Identify where cryptography is used across your applications, infrastructure, products and supply chain.

2. Prioritize long-lived data

Determine which information needs to remain confidential for ten years or more, making it potentially vulnerable to HNDL attacks.

3. Assess technology dependencies

Understand which systems depend on RSA, ECC or other vulnerable public key algorithms.

4. Build cryptographic agility

Design future systems so cryptographic algorithms can be updated without major architectural changes.

5. Begin testing PQC

Evaluate standardized algorithms in representative environments to understand performance, interoperability and deployment considerations.

6. Develop a migration roadmap

Migration should be viewed as a multi-year program rather than a single technology upgrade.

Breaking the transition into manageable phases helps reduce operational risk while allowing organizations to align migration with existing technology refresh cycles.

Preparing for the quantum era starts today

Quantum computing has the potential to transform industries ranging from pharmaceuticals to logistics and materials science.

It also represents one of the most significant challenges modern cryptography has ever faced.

The important point is not that quantum computers will suddenly make today’s encryption obsolete overnight. Rather, organizations must recognize that cryptographic migration takes time.

The publication of standardized post-quantum algorithms means the industry now has a clear direction of travel.

The challenge is no longer deciding whether quantum-safe cryptography is necessary. It is determining how to introduce it effectively, efficiently and at scale.

Organizations that begin preparing today will have the opportunity to modernize their security strategically, reducing operational risk while protecting long-term data confidentiality.

Those that delay may ultimately find themselves managing a far more disruptive transition under greater time pressure.

Quantum computing cybersecurity is about building the resilient, adaptable cryptographic foundations that organizations will rely on for decades to come.

Preparing for quantum-safe security

The transition to quantum-safe security requires careful planning, cryptographic expertise and a clear understanding of your organization’s unique technology landscape.

Whether you’re assessing your current cryptographic posture, planning a migration roadmap or optimizing post-quantum implementations, PQShield can help you build a practical path to quantum-safe security. Speak to our experts today.