What Is Post-Quantum Cryptography and Why Are Computers Threatening Today’s Encryption?

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Every time you send a message, make an online payment, log into a website or access a private account, some form of cryptography is helping protect your information.

Most people never see this protection working. It operates behind websites, mobile applications, banking systems, cloud services and other digital platforms. Yet much of the security that keeps modern communication private depends on mathematical problems that are extremely difficult for ordinary computers to solve.

Quantum computing could change that.

Quantum computers are designed to process certain problems differently from conventional computers. If researchers eventually build machines powerful enough to run particular quantum algorithms at scale, some of today's widely used public-key cryptographic systems could become vulnerable.

This is why post-quantum cryptography, often shortened to PQC, has become an important area of modern computer science.

What Is Post-Quantum Cryptography?

Post-quantum cryptography is the development of cryptographic methods designed to remain secure against attacks from both conventional computers and sufficiently powerful quantum computers.

The important point is that post-quantum cryptography does not mean using a quantum computer to protect your information.

Instead, researchers are designing new mathematical techniques that ordinary computers can use while making it difficult for a future quantum computer to break the protection.

This distinction matters because organizations do not need to replace all their existing computers with quantum machines. The goal is to change vulnerable cryptographic systems before quantum computers become capable of attacking them.

In 2024, the U.S. National Institute of Standards and Technology finalized three major post-quantum cryptography standards: ML-KEM for establishing shared encryption keys, and ML-DSA and SLH-DSA for digital signatures.

Why Is Quantum Computing a Threat to Encryption?

To understand the problem, you first need to understand why encryption works.

Modern public-key cryptography often relies on mathematical problems that are easy to perform in one direction but extremely difficult to reverse without the correct information.

For example, some established systems depend on the difficulty of factoring very large numbers. Others depend on mathematical problems involving elliptic curves.

An ordinary computer may need an impractical amount of time to solve these problems when the numbers become sufficiently large.

Quantum computers could change this situation.

A sufficiently capable quantum computer running Shor's algorithm could solve certain mathematical problems much more efficiently than classical computers. That creates a potential threat to widely used public-key systems based on factoring and discrete logarithms.

This does not mean that quantum computers can currently break the internet's encryption. The required large-scale, fault-tolerant quantum computers do not yet exist.

The concern is that sensitive information often needs to remain protected for many years, so waiting until such machines arrive could be too late.

What Is the "Harvest Now, Decrypt Later" Problem?

One of the reasons organizations are preparing now is a strategy often described as harvest now, decrypt later.

Imagine an attacker intercepts encrypted information today. The attacker may not have the ability to read it now, but could store it.

If a powerful enough quantum computer becomes available in the future and the encryption used to protect that information is vulnerable, the stored data could potentially be decrypted.

This is especially important for information that has a long confidentiality period.

Government records, financial information, medical data, intellectual property and other sensitive material may still have value years after it was originally transmitted.

Therefore, quantum security is not only about protecting tomorrow's information. It can also involve protecting information being transmitted and stored today.

How Does Post-Quantum Cryptography Work?

Post-quantum cryptography does not rely on one single mathematical technique.

Researchers have investigated several families of mathematical problems that are believed to remain difficult for quantum computers.

One important approach uses lattice-based cryptography.

A lattice is a mathematical structure that can be represented as a regular arrangement of points in space. Certain computational problems involving high-dimensional lattices are believed to be difficult to solve efficiently, including for known quantum algorithms.

NIST's ML-KEM standard is based on the computational difficulty of a problem called Module Learning With Errors. ML-DSA also uses lattice-based mathematics for digital signatures.

Another approach uses hash functions. NIST's SLH-DSA standard uses a hash-based design and provides a different mathematical foundation from ML-DSA.

Having different approaches matters because cryptographic security should not depend entirely on one family of mathematical assumptions.

What Are Digital Signatures?

Post-quantum cryptography is not only about hiding information.

Digital signatures are also important because they help verify who created or approved digital information.

When you receive digitally signed software, documents or communications, a signature can help confirm that the content came from the expected source and has not been altered.

Some current digital signature systems rely on mathematical problems that could eventually be threatened by quantum computing.

Post-quantum signature algorithms are therefore being developed to provide the same basic function while resisting known quantum attacks.

NIST's ML-DSA and SLH-DSA are examples of standardized post-quantum digital signature systems.

Is Post-Quantum Cryptography Already Being Used?

The transition has already started.

NIST finalized its first three post-quantum standards in August 2024 and has encouraged organizations to begin migrating their systems. The migration involves identifying where vulnerable cryptographic algorithms are being used and replacing or updating them.

This process is more complicated than installing a new application.

Cryptography can be deeply embedded in websites, mobile devices, operating systems, banking infrastructure, cloud services, communication protocols and hardware.

An organization may therefore need to discover every place where older cryptographic systems are being used before it can replace them safely.

What Is ML-KEM?

ML-KEM is one of the most important names you will encounter when studying post-quantum cryptography.

It stands for Module-Lattice-Based Key-Encapsulation Mechanism.

A key-encapsulation mechanism helps two parties establish a shared secret over a public communication channel. That secret can then be used with symmetric encryption to protect the actual communication.

NIST standardized ML-KEM as FIPS 203. It is intended to serve as a general-purpose post-quantum method for establishing encryption keys.

You do not need to understand the underlying mathematics to understand its purpose. Its job is essentially to help two communicating systems establish a secret that an attacker cannot practically recover, even when considering future quantum capabilities.

Is Post-Quantum Cryptography the Same as Quantum Cryptography?

No.

The names sound similar, but the technologies are different.

Post-quantum cryptography uses mathematical algorithms that can operate on conventional computers. It aims to protect existing digital infrastructure from future quantum attacks.

Quantum cryptography uses principles of quantum physics as part of the security system itself.

Post-quantum cryptography is therefore particularly attractive for large-scale migration because organizations can deploy the algorithms through software, hardware and protocol updates without requiring a quantum communication network.

Does Quantum Computing Threaten All Encryption?

No.

This is an important distinction.

Quantum computing creates a particularly serious concern for certain public-key cryptographic systems. Symmetric cryptography and hash functions are affected differently.

Known quantum algorithms do not simply make every encryption method useless overnight.

The response therefore does not involve abandoning all cryptography. Instead, researchers are identifying vulnerable systems and developing replacements or appropriate adjustments.

NIST's transition work distinguishes between different types of cryptographic systems and their exposure to quantum attacks.

What Is NIST Doing About the Quantum Threat?

NIST has spent years running an international process to evaluate candidate post-quantum algorithms.

The organization finalized ML-KEM, ML-DSA and SLH-DSA in 2024. It has continued evaluating additional algorithms to provide alternatives and backup options.

In March 2025, NIST selected HQC as an additional algorithm for post-quantum encryption. HQC uses a different mathematical approach from ML-KEM and is intended to provide a backup option rather than replace ML-KEM as the primary general encryption standard.

This continued evaluation reflects an important principle in cryptography: security improves when researchers continually test systems instead of assuming that today's solution will remain perfect forever.

What Does This Mean for Students and Internet Users?

You probably will not need to manually install a post-quantum algorithm on your phone tomorrow.

The transition will largely happen through updates to the technology and services you already use.

However, understanding the issue is valuable because post-quantum cryptography sits at the intersection of mathematics, computer science, cybersecurity and emerging technology.

Students interested in cybersecurity should understand why encryption methods need to evolve.

Those studying mathematics can see how abstract mathematical problems become the foundation of global digital security.

Computer science students can also see how a change in computing technology can force an entire industry to reconsider assumptions that once seemed reliable.

Why Is the Transition Happening Before Quantum Computers Arrive?

Security infrastructure takes time to change.

Large organizations may operate thousands of systems, some of which may contain cryptographic technology that was installed many years ago.

Replacing those systems requires testing, software development, hardware updates, compatibility checks and careful deployment.

There is another reason for starting early: nobody can say exactly when a sufficiently powerful quantum computer capable of threatening today's vulnerable public-key systems will become available.

Preparing in advance gives organizations time to identify weaknesses and complete the transition without waiting for a crisis.

Conclusion

Post-quantum cryptography is an effort to prepare digital security for a future in which powerful quantum computers could challenge some of today's most widely used cryptographic systems.

The technology is not about replacing ordinary computers with quantum computers. It is about developing mathematical methods that conventional digital systems can use while resisting known quantum attacks.

The transition has already moved beyond theoretical research. Major standards such as ML-KEM, ML-DSA and SLH-DSA have been finalized, while additional algorithms such as HQC are being developed as part of a broader effort to strengthen long-term digital security.

For students, the lesson is broader than encryption itself. Technology changes, and when it does, the mathematical and scientific foundations supporting that technology must evolve with it.

This educational content was carefully researched and prepared by the editorial team at Labari Web Education to support students, researchers, educators, and lifelong learners. Our goal is to provide practical, accurate, and easy, to, understand resources for JAMB, POSTUTME, WAEC, WAEC/GCE, NECO, undergraduate studies, postgraduate research, thesis and dissertation writing, academic success, scholarships, and career development. While every effort is made to ensure accuracy, readers are encouraged to verify official information where applicable.

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