The short version
Almost everything private you do online like logging into your bank, sending a message, entering a password, paying for something is protected by encryption. That encryption works because certain math problems are too hard for today's computers to solve in any reasonable amount of time.
Quantum computers change that assumption. A large enough quantum computer could solve some of those "too hard" problems quickly and break a big chunk of the encryption the internet relies on.
That machine doesn't exist yet. But the threat is already here, for a reason we'll explain. And the world's security agencies are already rolling out replacement encryption designed to survive quantum attacks. This article explains, what the threat is, why it matters today, and what's being done about it.
How encryption protects you right now
When you see the padlock in your browser, two different kinds of encryption are working together.
Symmetric encryption uses a single shared secret key to lock and unlock data. It's fast and strong. The catch: both sides need the same key so how do they agree on a secret key over the open internet without anyone seeing it?
Public-key encryption (also called asymmetric encryption) solves that. Everyone has two mathematically linked keys:
A public key they share openly, anyone can use it to lock a message to them.
A private key they keep secret, only it can unlock those messages.
The magic is that knowing the public key doesn't let you figure out the private key. This is what lets two strangers establish a secure connection without ever having met. The most common public-key systems are RSA and ECC (elliptic-curve cryptography), and they protect almost every secure website, VPN, and messaging app today.
Here's the key insight: public-key encryption is secure only because of one assumption that deriving the private key from the public key requires solving a math problem so hard it would take today's computers millions of years. For RSA, that problem is factoring a very large number into its prime components. Easy to multiply two big primes together; effectively impossible to reverse.
That single assumption is what quantum computers threaten.
What a quantum computer actually does differently
A normal computer stores information in bits, each either a 0 or a 1. It checks possibilities one effective path at a time.
A quantum computer uses qubit, which exploit two strange properties of quantum physics:
Superposition — a qubit can represent a blend of 0 and 1 at the same time, so a group of qubits can encode an enormous number of combinations simultaneously.
Entanglement — qubits can be linked so they act as a coordinated system rather than independent parts.
The result isn't "a faster regular computer." It's a fundamentally different machine that can attack certain specific problems by exploring many possibilities in a coordinated way, instead of plodding through them one by one.
Crucially, quantum computers are not better at everything. They're dramatically better at a small set of problems and, unluckily for us, the math behind RSA and ECC is on that list.
The two algorithms that change the game
Two known quantum algorithms are the reason cybersecurity experts are paying attention.
Shor's algorithm — the serious threat.
In 1994, mathematician Peter Shor showed that a sufficiently powerful quantum computer could factor large numbers (and solve the related elliptic-curve problem) efficiently. That's precisely the "impossible" problem RSA and ECC depend on. In plain terms: Shor's algorithm would break the public-key encryption protecting the internet today. Not weaken it but actually break it.
Grover's algorithm — the manageable threat.
Grover's algorithm speeds up brute-force searching, which affects symmetric encryption (like AES). But it only provides a "square-root" speedup roughly, it halves the effective strength. The fix is simple: use bigger keys. AES-256 remains considered safe against quantum attacks. So symmetric encryption survives with minor adjustments; it's public-key encryption that needs replacing.
So, the headline is narrower and more precise than "quantum breaks everything": quantum computers primarily break the public-key encryption used to set up secure connections, while symmetric encryption mostly survives by using larger keys.
Why this is a problem today, not in 20 years
The obvious objection: today's quantum computers are small and error-prone. Experts estimate it may be a decade or more before one is powerful enough to run Shor's algorithm against real keys. So why worry now?
The answer is a strategy called “Harvest Now, Decrypt Later."
An attacker doesn't need a quantum computer today to benefit from one tomorrow. They can record encrypted data now intercepted traffic, stolen encrypted databases, captured communications and simply store it. When a capable quantum computer eventually exists, they decrypt everything they saved.
This matters enormously for any data that must stay secret for years: medical records, state secrets, financial data, intellectual property, and the long-lived encryption keys baked into hardware and infrastructure. Data you send today could be decrypted in ten years. For a lot of sensitive information, that's well within its required secrecy lifetime.
That's why governments and major companies are migrating now, before the threat is live. The migration itself takes years, so waiting for the quantum computer to arrive is already too late.
The fix: post-quantum cryptography
The solution is post-quantum cryptography (PQC) new public-key encryption algorithms built on math problems that both regular and quantum computers find hard. PQC runs on the ordinary computers and phones we already use; it doesn't require any quantum hardware. It simply swaps the underlying math for something Shor's algorithm can't unravel.
Most leading PQC schemes are based on problems involving structured lattices. Think of a vast multidimensional grid where finding the shortest path or nearest point is brutally hard to do in reverse, even for a quantum computer.
In 2024, the U.S. National Institute of Standards and Technology (NIST) finalized the first official PQC standards after an eight-year worldwide competition. The headline algorithms:
ML-KEM (originally called Kyber) — for securely establishing shared keys, the job RSA/ECC do today during connection setup.
ML-DSA (originally Dilithium) and SLH-DSA (SPHINCS+) — for digital signatures, which prove authenticity and integrity.
These are now real, published standards. Major platforms have already started deploying them. For example, modern versions of secure messaging and web browsers have begun using hybrid schemes that combine a traditional algorithm with a post-quantum one, so you're protected even if one of them is later found weak.
What this means for you and your organization
You don't need to panic, and you don't need a quantum physics degree. But if you work in or around technology, here's the practical takeaway:
Awareness is the first step. Quantum is no longer science fiction in security circles, it's an active migration project at every serious institution.
Inventory your cryptography. Organizations are being advised to find out where and how they use public-key encryption, because you can't replace what you can't see. This is the unglamorous but essential first move.
Prioritize long-lived secrets. Data that must remain confidential for many years is most exposed to "Harvest Now, Decrypt Later," so it should migrate first.
Favor "crypto-agility." Build systems so the encryption algorithm can be swapped out without rebuilding everything. The lesson of this whole episode is that no algorithm is forever.
Adopt the standards, don't invent your own. The NIST PQC standards exist precisely so individual teams don't roll their own. Use vetted libraries.
The takeaway
Quantum computing isn't going to break the internet overnight, and the sky is not falling. But it represents a rare event in cybersecurity: a predictable future threat, visible years in advance, against which we can prepare deliberately rather than react in a panic.
The story is genuinely optimistic. We understood the threat (Shor's algorithm) decades before the machine to exploit it exists. We ran a global, open competition to design defenses. And we now have published, standardized, deployable replacements. The remaining work is migration — careful, large-scale, and already underway.
The internet's encryption is being quietly rebuilt to survive the quantum age. Now you have the context to understand the shift and keep your third eye vigilant.