Quantum Computing vs Crypto: How Real Is the Threat?

Not long ago, I was asked about quantum computing and the threat it could pose to blockchain technology. It’s a question I’ve encountered repeatedly across discussions of various protocols, and the persistence of that curiosity suggests a genuine underlying concern. In this article, I aim to address those fears directly — so crypto holders can better understand the risks and move forward with confidence, rather than constantly looking over their shoulder.

A quantum computer is a device that performs computation using the principles of quantum mechanics, most notably superposition and entanglement to solve problems that are intractable for classical machines. While traditional computers process information as bits (0s and 1s), quantum computers use qubits, which can exist in a superposition of both states simultaneously. This fundamental difference allows quantum systems to explore many possibilities at once, offering the potential for exponential speedups in fields such as molecular simulation, optimization, and cryptography. The real concern lies in this potential for exponential speedups in solving cryptographic problems.

Most crypto wallets such as those used in Bitcoin or Ethereum rely on a pair of keys: a private key, which acts as a secret password, and a public key, which functions like a lock visible to everyone. The security of this system is based on a simple premise: it is easy to create the lock, but extraordinarily difficult to reverse it without the private key. For classical computers, deriving a private key from a public key would take millions if not billions of years, which is why these systems are considered secure today. Quantum computing, however, threatens to fundamentally change that assumption.

The ability for quantum computers to use superposition allows them to test many keys at once therefore permitting them to crack the private key within hours or days. In fact, there’s a quantum algorithm called Shor’s algorithm that can take a public and efficiently figure out the private key. A complete disaster for crypto security.

Imagine your crypto wallet like this: you put a lockbox in public — that’s your wallet address, but only you have the key, which is your private key. Today, even if everyone can see the lockbox, they can’t open it. With quantum computers, however, someone could see your lockbox and reverse engineer the key. In other words, when quantum computers get powerful enough, a person can steal funds from exposed wallets.

A wallet isn’t “exposed” by default. It becomes exposed when your public key is revealed on-chain in a usable way. Most people assume their wallet address is their public key — but it’s not. A wallet address is actually a hashed version of the public key, which adds an extra layer of protection. However, the moment you spend from a wallet, your public key is revealed in the transaction data because the network needs it to verify your signature. And that’s the key point: the public key is what a quantum computer targets. With enough power, it could reverse the mathematics that keep the private key hidden — turning what is effectively impossible to break today into something that could eventually be cracked.

Think of it like this: your address is a masked identity, while your public key is your real face. As long as your face stays hidden, you’re protected. But once you reveal it — when you make a transaction — it becomes visible to everyone. Today, that’s harmless. But with a powerful enough quantum computer, someone could use that “face” to reconstruct your DNA — your private key.

It’s important to note that not everything breaks with the arrival of quantum computers. While digital signatures become vulnerable, the hashing functions that secure blockchain networks such as SHA-256 are far more resistant. The primary risk lies in ownership, not the collapse of the entire system. A sufficiently powerful quantum computer could potentially steal funds from exposed wallets or even forge transactions by impersonating their owners. So while the blockchain structure itself doesn’t suddenly collapse, it becomes cryptographically exposed at the user level.

So why aren’t people panicking yet? Simply put, we don’t have quantum computers powerful enough today to break these systems. However, building and upgrading cryptographic infrastructure takes years, so the prevailing mindset is: not urgent today, but dangerous to ignore. Blockchain networks can become quantum-resistant by upgrading to post-quantum signature schemes, but that transition won’t happen overnight. Users on those networks would also need to move their funds from currently vulnerable address types to newer, more secure ones — such as P2TR or future quantum-resistant formats.

The good news is that a quantum computer powerful enough to break Bitcoin- or Ethereum-style cryptography is not commercially available today. The machines that do exist are experimental research devices, often costing millions of dollars. That alone makes this type of attack inaccessible to most.

Beyond cost, the knowledge required is another major barrier. An attacker would need deep expertise in quantum computing, elliptic-curve cryptography, Shor’s algorithm, blockchain mechanics, and high-speed automated exploitation. The combination of both significant financial resources and advanced technical skill is extremely rare.

In reality, credible attackers would likely be governments, major research labs, or highly funded organizations — not random hackers. That said, the risk still exists, and it’s not something that should be taken for granted.

How to mitigate this today

The chances of your protocol becoming quantum-resistant in the near term are relatively low. That makes it important to act with precaution well before quantum computing becomes a real threat. I recommend a few practical steps. First, use a new address for each transaction to minimize exposure. Second, avoid leaving large amounts of funds in “used” addresses. Once you spend from a wallet, your public key is revealed on-chain. Lastly, consider using blockchain protocols that have the flexibility to upgrade their cryptography over time, such as Ethereum or Kaspa.

Blockchain is still a young industry, and the adage “what doesn’t kill you makes you stronger” applies here just as much as it does to individuals. Quantum computing is certainly a threat — but if the space adapts and evolves, it will ultimately emerge stronger because of it.

Quantum Computing vs Crypto: How Real Is the Threat? was originally published in Coinmonks on Medium, where people are continuing the conversation by highlighting and responding to this story.