What Is Quantum-Resistant Cryptography and How Does It Work?

Key takeaways

Quantum-resistant cryptography replaces traditional encryption methods with advanced systems built to withstand future quantum attacks. Here are some important things to know:

• The National Institute of Standards and Technology (NIST) finalized its first set of post-quantum encryption standards in 2024 to help organizations begin implementing modern security measures [1].

• Companies such as Google, IBM, and Cloudflare have already begun to implement quantum-resistant cryptography into their software and cloud systems.

• You can choose from quantum-resistant cryptography algorithms such as lattice-based, hash-based, and code-based algorithms to find the cybersecurity strategy best suited to your needs. 

Discover what quantum-resistant cryptography is and how to start using it to help you future-proof your data and protect your organization’s information. If you’re ready to learn more, enroll in the Cisco Cybersecurity Operations Fundamentals Specialization. You’ll have the opportunity to explore the cybersecurity landscape and learn core concepts like encryption, endpoint security, and cryptography.

What is quantum-resistant cryptography, and why does it matter?

Quantum-resistant cryptography, or post-quantum cryptography, refers to an emerging type of data security aimed at protecting information from quantum computers. Current digital security systems typically rely on mathematical problems that aren’t easily solved by most computers. For example, two standard encryption methods, RSA and Elliptic Curve Cryptography (ECC), protect data by making it nearly impossible for computers to guess the correct encryption key within a certain time limit. However, quantum computers pose a new challenge to these traditional security systems.

While traditional computers use “bits,” which code either a zero or a one, quantum computers are a new generation of computers that use “qubits,” which represent zero, one, or both at the same time. This “superposition” allows quantum computers to perform calculations more quickly. In theory, this capability could break the mathematical foundations of RSA and ECC encryption.

To overcome this security concern, quantum-resistant cryptography has been designed to withstand the computational power of quantum machines by relying on different, more complex types of mathematical problems. Essentially, quantum-resistant cryptography aims to future-proof data security before quantum computers become mainstream.

What is quantum encryption?

Quantum encryption, known as quantum cryptography, secures data using the rules of quantum physics rather than mathematical equations. It works by sending data in particles of light, which inherently change when tampered with. The result is that hackers find it much more difficult to view information undetected.

How does quantum-resistant cryptography work? Four algorithms

Quantum-resistant cryptography works by replacing mathematical problems that quantum computers can easily solve with new, more difficult types of problems. These problems are the foundation of several quantum-resistant cryptography algorithms. A few popular ones include the following. 

Lattice-based cryptography 

Lattice-based cryptography is a widely used quantum-resistant cryptography algorithm and a popular replacement for traditional algorithms. This algorithm relies on lattices, which are complex mathematical structures formed by combinations of vectors, and requires computers to solve problems such as finding the shortest or closest vector in the lattice. NIST-standardized examples of lattice-based algorithms include the ML-KEM (Module-Lattice-Based Key Encapsulation Mechanism) and ML-DSA (Module-Lattice-Based Digital Signature Standard).

Hash-based cryptography

With hash-based cryptography, computers use mathematical functions known as “hashes” to create secure digital signatures. In this type of system, each message or value you want to sign links to a unique random string, which then uses a hash function to transform and create a public key. Once you sign the message, the private key reveals itself, and you can verify its authenticity by hashing it and checking that it matches the public key. The difficulty of reversing a hash operation is what makes this technique quantum-resistant. A NIST-standardized example of hash-based cryptography is SLH-DSA (Stateless Hash-Based Digital Signature Standard).

Code-based cryptography

Code-based cryptography builds on the same idea used to fix errors when sending data. When computers send information, they add extra “check bits” to help detect and correct mistakes in the data. In cryptography, developers turned the same tool into a security measure by encoding messages in a way that only a computer with the right key can decode. Because of its reputation for reliability and effectiveness, professionals often choose this type of cryptography for secure communications. A widely popular example of this algorithm is the McEliece cryptosystem.

Multivariate polynomial cryptography

Multivariate polynomial cryptography is based on a system of multivariate polynomial equations that are difficult for computers to solve. Basically, multivariate cryptography creates a mathematical puzzle where only the computer with the correct key can find the right solution. Because solving these equations is so complex, this method is fast and practical for building quantum-resistant digital signatures and encryption systems. The Unbalanced Oil and Vinegar scheme is an example of the multivariate polynomial cryptography method.

Is AES-256 quantum-resistant?

AES-256 is partially quantum-resistant. AES-256 (Advanced Encryption Standard using 256-bit keys), is a widely used symmetric encryption algorithm often used by the US government and other secure organizations. While quantum computers could use an algorithm, called Grover’s algorithm, to reduce their effective security level from 256 bits to approximately 128 bits, most professionals still consider 128 bits as secure, meaning this algorithm is technically quantum-resistant. However, as quantum computing develops, organizations are keeping an eye on advancements to ensure encryption techniques, such as AES-256, can withstand potential future attacks. 

Read more: What Is Encryption and How Does It Work?

Who is using this technology? Quantum-resistant cryptography companies

Several major technology companies are already experimenting with quantum-resistant cryptography and implementing this tech to prepare for the future of cybersecurity needs. A few organizations making strides include:

• Google: Integrating hybrid post-quantum encryption to secure web traffic

• Cloudflare: Integrating post-quantum algorithms into cloud systems for free

• IBM: Integrating quantum-safe security protocols into hardware and software stacks

• PQShield: Creating quantum-safe cryptography on chips, in applications, and in the cloud

Quantum security and future outlook

Quantum computing is both an opportunity and a challenge for global cybersecurity systems. While current quantum computers can’t yet break mainstream cryptography schemes, many companies believe it’s only a matter of time. This creates what companies know as the “store now, decrypt later” threat, when attackers collect encrypted data and wait for quantum technology to advance so they can decrypt it later. As a result, information users assume to be secure now might not remain so in the future.

To address this concern, NIST led a multi-year global effort to develop quantum-resistant cryptography algorithms that can hold up against quantum attacks. In 2024, the organization finalized its first set of post-quantum encryption standards, including both lattice- and hash-based designs [1]. This was a major milestone toward more mainstream quantum-safe security and included encryption standards aimed at everything from email messages to e-commerce transactions. While quantum computing can revolutionize fields such as medicine and artificial intelligence (AI), our data security measures must evolve alongside it. Building a secure quantum future is not only a technological priority, it’s a necessity to maintain global trust, privacy, and security. 

What are the main challenges in developing and implementing quantum-resistant cryptography?

Developing and implementing quantum-resistant cryptography presents a few challenges that may influence its path to widespread adoption. One of the biggest is performance, as quantum-resistant systems tend to require much larger encryption keys than traditional methods. This can reduce the speed of operations and raise storage and bandwidth requirements. For older, legacy infrastructures, this may mean companies require upgrades to fully take advantage of new systems. 

Another challenge is the reliability of quantum-resistant methods over time. As quantum-resistant cryptography advances, so might quantum computing, meaning that it’s important for cybersecurity researchers and developers to continually update and replace algorithms. However, despite hurdles, quantum-resistant cryptography remains a practical near-term solution for defending against quantum threats and represents promise when it comes to keeping our data safe. 

Getting started with quantum-resistant cryptography

Getting a head start on future-proofing the data security systems in your organization may save you a headache later on. While this will look different depending on your data, a few ways you can start learning about and using quantum-resistant cryptography include:

• Identifying vulnerabilities to quantum threats in your data and systems.

• Testing early-stage quantum-resistant cryptographic algorithms in non-critical systems.

• Collaborating with industry and government agencies to stay up-to-date on advancements.

• Planning a phased strategy to replace current encryption methods with quantum-safe strategies.

If you’d like to work with developing the technology directly, earning a degree in cybersecurity, taking online courses, or even exploring media (such as listening to podcasts) can help you build the foundational skills needed to enter a career in this area.

Explore our resources for cybersecurity professionals

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• Take the Quiz: Cybersecurity Career Quiz: Is It Right for You? 

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