Quantum: Hard Truths & Hard Forks

Artificial intelligence has made huge strides over the past year, pushing boundaries and raising big questions. One of them: How close are we to real quantum computing — and what threat does that pose to Bitcoin? At its most extreme, quantum computing could break Bitcoin’s cryptography. If attackers could derive private keys from public ones, they could forge transactions and undermine the system.

Sure, quantum-resistant cryptography exists. And yes, Bitcoin could upgrade. But that raises a deeper question: Can Bitcoin actually change when it needs to? What does its history of hard forks and minimal upgrades tell us about its capacity to adapt?

TLDR: I don’t lose sleep over the quantum threat - but we must prepare for the upgrades that will inevitably be required and use the opportunity to deepen our understanding of the protocol.

What is Quantum Computing?

Quantum computing is a new type of computing which uses the principles of quantum mechanics. Quantum computers use qubits which can exist in superpositions, enabling parallel computations across many possible states. Quantum computers could, in theory, solve certain problems way faster than classical computers. The sudden explosion in artificial intelligence has led many to speculate that the time horizon to creation of widely available and stable quantum computers might be closer than initially expected.

Why is QC a threat to bitcoin?

Bitcoin utilizes cryptography, and it relies on a number of underlying cryptographic algorithms. The one that will likely come under threat from QC is the Elliptic Curve Digital Signature Algorithm (ECDSA). This is a critical component in the relationship between Bitcoin public keys and private keys, which is designed as a one-way function. It’s easy to generate a public key from a private key, but it is practically impossible to derive a private key from a public key. For example, we estimate that it could take trillions of years to brute-force a Bitcoin private key from its corresponding public key.

In Bitcoin, public keys are visible on-chain — so it is vital that attackers cannot derive private keys from them. With the advent of quantum computing, we could imagine a world where deriving private keys from public keys becomes trivial. In that case, an attacker could forge a digital signature, impersonate a wallet owner, and spend their Bitcoin. This obviously presents a significant threat to Bitcoin.

It’s worth noting, however, that not all Bitcoin addresses reveal their public keys on the blockchain. If a wallet has never spent any Bitcoin, the full public key remains hidden. Only once Bitcoin has been sent from an address is the full public key revealed. This means that addresses which have already broadcast a transaction could be at greater risk under a quantum scenario.

This reinforces the best practice in Bitcoin security: generating a new address each time you receive Bitcoin. While this is primarily a privacy-preserving practice, here we see that it may also offer long-term security benefits.

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Should I be worried?

QC Horizon is Distant

Quantum computers do exist today, but not in a way that threatens modern cryptographic systems. Companies like IBM and Google have developed quantum machines, but they are still noisy, error-prone, and face major physical and stability challenges. The real breakthrough would be in developing fault-tolerant quantum machines — computers that can correct their own errors and run large, reliable programs. Most realistic expert forecasts suggest this is still 10–15 years away.

A Broader Cryptographic Challenge

Importantly, quantum computing doesn’t just threaten Bitcoin — it threatens all modern security systems. ECDSA and other cryptographic algorithms are used by banks, insurance firms, asset managers, and even national security agencies. Any institution that stores sensitive data or capital relies on these cryptographic standards.

So if fault-tolerant quantum computers suddenly became available and fell into adversarial hands, you would expect them to target the largest honeypots first — centralized financial institutions and government databases — rather than Bitcoin, which is more distributed and harder to attack at scale.

How the World is Preparing

The cryptography community has been actively preparing for this threat. The U.S. National Institute for Standards and Technology (NIST) ran a multi-year competition from 2016 to 2022 to identify post-quantum cryptographic algorithms. Hundreds of cryptographers participated, and NIST has now published a shortlist of quantum-resistant algorithms.

Potential candidates for post-quantum cryptography in Bitcoin include XMSS, SPHINCS+, or lattice-based schemes like Dilithium, though these are generally slower and require larger signatures (sometimes 1–2 KB instead of 64 bytes).

The bigger challenge now lies in upgrading all the systems — financial, institutional, governmental, and decentralized — that still run on classical cryptographic standards. Everyone will need to upgrade eventually. The questions are simply when and how.

How does bitcoin upgrade?

Bitcoin can obviously upgrade its cryptographic technology, but the process is more complex in open source decentralized system than in centralized systems. Bitcoin is a decentralized network, and by design, changes to its protocol are deliberately difficult to make. This is a feature, not a bug — it’s part of what ensures Bitcoin’s long-term stability and trustworthiness.

For example, we do not want to casually change Bitcoin’s supply schedule or consensus rules, because doing so would compromise the clarity, predictability, and scarcity that underpin its value proposition. Bitcoin provides a “monetary true north” in a world of shifting fiat baselines.

In contrast, centralized systems — while still facing technical hurdles when upgrading — can roll out changes much more easily because they don’t require broad community consensus or decentralized coordination.

Usually bitcoin's software upgrades take place via soft-forks, which are backwards compatible - this means that the old software is still compatible with the new software. I.E. The software still works, even if you don't upgrade.

An upgrade to a quantum computing resistant cryptographic algorithm will probably not be backwards compatible, and will thus constitute a hard-fork. I.E. the old software may not work after the upgrade. Whether they are aware of it or not, users will make an active choice between the different pieces of software. If some users fail to upgrade, it can result in a split in the chain. I.E. two different versions of bitcoin

Chain splits have happened in bitcoin before (for example, Bitcoin Cash and Bitcoin SV), and they will happen again. However, it is preferable to minimise the chain split as much as possible. I.E. We want a large majority to come to a consensus about the cryptographic algorithms used within bitcoin.

It can take time to reach this type of consensus, hence the importance of discussing these questions. In this regard I am encouraged that conversations have begun amongst core bitcoin developers regarding quantum computing. For example, BIP 360: Pay to Quantum Resistant Hash (P2QRH) and Quantum-Resistant Address Migration Protocol (QRAMP)

Why is this important for you?

Quantum computing doesn’t worry me today - but part of Bitcoin’s strength is that it encourages us to think long-term and consider all possibilities. Its resilience doesn’t come from ignoring threats, but from openly confronting them. And in this case, the right conversations have already begun.

Bitcoin is the most powerful technology since the internet. It has the ability to change the world in ways that we cannot imagine and it has made unprecedented progress in its 15 years of operation. 15 years is not a long time - bitcoin is still a relatively new digital technology. While incredibly stable and unchanging, it may still need to evolve.

If the quantum computing threat does emerge in the decades ahead, its earliest targets are likely to be institutions with greater concentrations of capital or data than Bitcoin. While all systems will eventually need to upgrade, Bitcoin's decentralized nature makes early preparation even more essential.

Bitcoin doesn’t wait for the future to arrive - it builds toward it. That’s the mindset we need now.