The importance of quantum-safe communication: post quantum cryptography (PQC) and quantum key distribution (QKD)

Securing Sensitive Data with Public Key Cryptography

In today’s digital world, the protection of sensitive communication relies heavily on public key cryptography. Developed in the 1970s, this techniques enable secure and scalable communications over the internet and across networks.

The primary functions of public key cryptography include key agreement, which establishes a secure key between parties for encrypting sensitive information, and digital signatures, which verify identity and build trust between entities. The security of public key cryptography is rooted in complex mathematical algorithms, such as large-number integer factorisation and discrete logarithm calculations. These calculations are extremely challenging for today’s classical computers to solve, ensuring sensitive data and communications remain safeguarded against unauthorised access.

The Quantum Computing Threat to Long-Term Data Security

While it would take classical computers thousands of years and immense financial and computational resources to break the forms of public key cryptography that are widely used today, quantum computers pose a far greater risk. Leveraging the principles of quantum mechanics, these advanced systems can execute tasks significantly faster than today’s computers. For instance, a sufficiently powerful quantum computer could utilise Shor’s algorithm to compromise the security provided by all of the commonly-used public key algorithms used to protect communications today.

This capability means that quantum computing could render the commonly used forms of public key cryptography insecure, allowing sensitive data to be accessed by malicious actors. Moreover, bad actors can collect and store encrypted data today, with plans to decrypt it later when quantum computers become widely accessible—a strategy known as harvest-and-decrypt attacks. The implications for long-term data security are profound. Critical data that must remain secret for extended periods, such as financial records, medical information, corporate data, and infrastructure systems, are particularly vulnerable. Preparing for the quantum computing era is essential to safeguard these sensitive assets.

To safeguard sensitive data against the risks posed by quantum computing, it is essential to make communications quantum safe—protected from quantum-computing-based cryptographic attacks.

Two primary methods are being developed and implemented today to achieve quantum-safe encryption: Quantum Key Distribution (QKD) and Post Quantum Cryptography (PQC). These approaches play a crucial role in ensuring the resilience of encryption systems in the face of the growing quantum computing threat.

What is Quantum Key Distribution (QKD)?

Quantum Key Distribution (QKD) is a method for generating and sharing encryption keys that are resistant to attacks from quantum computing. Unlike traditional methods, QKD leverages physical particles, such as photons, to create fundamentally secure encryption keys that cannot be observed or compromised.

The security of QKD is grounded in the principles of quantum physics. By relying on the behaviour of physical particles rather than mathematical algorithms, QKD is immune to attacks from both quantum computers and classical computing systems. Globally recognised protocols, such as BB84, form the foundation of QKD and have been rigorously peer-reviewed with proven security guarantees.

Currently, QKD is mainly deployed over optical fibres, with potential future applications in satellite communication. A typical deployment involves the exchange of quantum states between two parties (commonly referred to as Alice and Bob), followed by secure processing to generate quantum-safe keys that encrypt and decrypt sensitive information.

Quantum Key Distribution (QKD) is a method for generating and sharing encryption keys that are resistant to attacks from quantum computing. Unlike traditional methods, QKD leverages physical particles, such as photons, to create fundamentally secure encryption keys that cannot be observed or compromised.

The security of QKD is grounded in the principles of quantum physics. By relying on the behaviour of physical particles rather than mathematical algorithms, QKD is immune to attacks from both quantum computers and classical computing systems. Globally recognised protocols, such as BB84, form the foundation of QKD and have been rigorously peer-reviewed with proven security guarantees.

What is the Current Status of Quantum Key Distribution (QKD)?

Research and development on Quantum Key Distribution (QKD) has been ongoing for over 20 years, resulting in the deployment of commercial QKD systems across various sectors and diverse use cases globally. Today, QKD can be seamlessly integrated into existing fibre networks and data services. This enables organisations to implement quantum-safe solutions immediately, offering robust protection against quantum-computing-based cryptographic attacks.

QKD Deployment Considerations

While Quantum Key Distribution (QKD) offers fundamental security and immunity against quantum-computing-based cryptographic attacks, it is a hardware-based solution that comes with associated financial costs. Additionally, as an optical technology, QKD requires deployment over fibre networks, and in the future, satellite networks will further expand its reach. As a result, QKD is currently best suited for network core, metro, and edge deployments where uncompromising security is essential.

Innovations by QKD manufacturers are addressing these challenges. For example, Twin Field QKD is extending the range of QKD in fibre networks, effectively reducing costs. Similarly, advancements in ‘QKD systems on a chip’ are dramatically lowering deployment costs, paving the way for QKD adoption in mass markets.

The future introduction of satellite-based QKD services will enable global coverage, providing secure quantum-safe communication even in remote areas where fibre networks are unavailable. This development will significantly enhance connectivity for potential users worldwide.

What is Post Quantum Cryptography (PQC)?

Post Quantum Cryptography (PQC) refers to software-based cryptographic algorithms specifically designed to resist attacks from quantum computers. PQC employs new mathematical problems for which no attack with a quantum computer is known.

Some of the most researched PQC methods include lattice-based, code-based, ECC isogeny, hash-based, and multivariate cryptographic schemes. These approaches are significantly harder to compromise than the mathematical techniques used in current cryptographic systems.

It’s important to note that the security of PQC algorithms relies on computational and mathematical assumptions, rather than physical principles like Quantum Key Distribution (QKD). This means PQC provides resistance to known quantum-computing-based cryptographic attacks but may still face vulnerabilities from future advancements in quantum computing or mathematical techniques.

Given the unpredictability of breakthroughs in mathematics and quantum computer science, no mathematics-based encryption scheme can guarantee absolute security. Therefore, PQC is considered a strong defensive measure, though not an infallible solution, against future quantum computing threats.

What is the Current Status of Post Quantum Cryptography (PQC)?

In August 2024, following research that began in 2016, the US-based National Institute of Standards and Technology (NIST) released the first set of Post Quantum Cryptography (PQC) standards. These include FIPS 203, 204, and 205, which address cryptographic key exchange and digital signatures to defend against cyberattacks by quantum computers.

In October 2024, NIST also announced 14 candidate algorithms for digital signatures. These algorithms are currently being evaluated for their performance and potential standardisation. Several rounds of assessment are expected before draft standards are developed and formal standards are eventually released.

Real-world trials and pilot implementations of the newly released PQC standards have already commenced. Organisations are integrating PQC algorithms into their existing cryptographic infrastructures to test their performance and ensure compatibility. These trials are critical for identifying potential challenges and shaping strategies for large-scale deployments.

As the field progresses, additional PQC candidates are likely to undergo evaluation, standardisation, and real-world testing, paving the way for widespread deployment across global communication networks.

Post Quantum Cryptography (PQC) Deployment Considerations

Post Quantum Cryptography (PQC) is widely regarded as offering resistance to cryptographic attacks from quantum computers, but it cannot guarantee absolute security. Future advancements in quantum computing, computer science, or mathematics may potentially compromise the algorithmic properties of PQC.

As a software-based solution, PQC is often viewed as a quick, cost-effective upgrade to enhance a network’s cryptographic capabilities. However, deploying and integrating PQC algorithms into legacy network infrastructures presents notable challenges.

Today’s networks, IoT ecosystems, and user devices have evolved around today’s forms of public key cryptography, meaning the transition to PQC requires careful consideration:

• Larger private keys: PQC private keys are significantly larger than those used currently used in public key cryptography, necessitating increased storage and bandwidth across networking, edge, and IoT devices.
• Increased computational demands: PQC algorithms may impose higher computational requirements, potentially slowing down network devices or necessitating compute power upgrades.
• Integration challenges: Seamlessly incorporating PQC into existing networking protocols while maintaining compatibility with other methods of public key cryptography across networks and devices is likely to be an iterative process requiring time and effort.

Enterprises are encouraged to proactively consult their IT system and network providers about plans for integrating PQC into their products. This process may involve partial or full upgrades to networks and user devices, with both financial and logistical implications.

Another critical factor is the time required for a complete cryptographic assessment of the network. Developing a quantum-safe migration plan, ensuring proper PQC integration with existing protocols, meeting corporate and regulatory security requirements, and executing phased upgrades are complex and time-intensive tasks. The operational and financial implications of this transition must be thoroughly evaluated and carefully planned.

Strength in Depth

A hybrid approach integrates cryptographic information from both Quantum Key Distribution (QKD) and Post Quantum Cryptography (PQC), representing a critical step toward ensuring long-term security for network infrastructures.

By combining QKD and PQC, organisations can base their security on a broader range of cryptographic challenges, effectively mitigating potential quantum-computing-based attacks and strengthening overall resilience. This hybrid QKD-PQC key approach ensures that even if one method fails, the combined key remains secure. For an attacker to compromise the secret key, they would need to simultaneously break both QKD and PQC.

Preparing for the Quantum Transition

Transitioning to quantum-safe networking is a complex process that may require substantial operational and financial resources. More critically, achieving full quantum safety could take significant time, leaving organisations vulnerable to the looming threat of quantum-computing-based attacks. The timeline for when quantum computers will be capable of breaking traditional forms of public key cryptography, often referred to as “Q-day,” is uncertain. Estimates suggest Q-day could occur within the next five years.

Numerous published guides provide frameworks for developing quantum cryptography migration plans. Common themes across these guides include:

• Address the quantum threat now: Large organisations should incorporate the risks of quantum computing-based attacks into their current security strategies.
• Raise awareness and define responsibilities: Create organisational awareness of the quantum threat and allocate resources and ownership for assessing the risks and potential solutions.
• Assess your cryptographic estate: Map your network, endpoints, applications, and data to identify the cryptographic methods currently securing them.
• Prioritise critical systems: Determine which network segments, data paths, and priority systems—such as those processing sensitive data or requiring long-term security—should transition first.
• Collaborate with experts: Work with external bodies, vendors, and experts to evaluate available technologies and identify suitable solutions.
• Develop a phased migration plan: Start with the most vulnerable, business-critical systems and gradually roll out quantum-safe protections across the entire network.
• Leverage QKD and PQC: Combine the strengths of Quantum Key Distribution (QKD) and Post Quantum Cryptography (PQC) to secure strategic network segments, reduce implementation time, lower CAPEX, and maintain flexibility.