BITCOIN VS. QUANTUM COMPUTERS
Share
Bitcoin is often presented as a digital fortress, a near-invincible system forged by cryptography and decentralization. For over fifteen years, it has resisted hackers, hostile states, and economic attacks. Yet, in the shadow of the world's most advanced laboratories, another technological revolution is taking shape: the quantum computer. Thanks to its qubits capable of existing in multiple states simultaneously, and the entanglement that instantly connects distant particles, the quantum computer promises computing power unimaginable for classical computers. And with it, the theoretical ability to break certain cryptographic systems previously considered indestructible.
To understand what's at stake, it's important to remember that Bitcoin is based on two pillars: the SHA-256 hash function, used to secure block integrity and mining, and the ECDSA signature algorithm, which allows anyone to prove ownership of their bitcoins when they spend them. When you receive bitcoins, your address is generated from a hash of your public key, a process that keeps your public key hidden until you spend your funds. This is essential security: an unrevealed public key cannot be attacked, even by a quantum computer. However, the moment you send your bitcoins, your public key becomes visible on the network, opening a theoretical window of vulnerability.
This is where Shor's algorithm comes in, a quantum physics feat that allows problems considered insoluble with a classical computer, such as factoring large numbers or calculating discrete logarithms, to be solved in polynomial time. However, breaking ECDSA is precisely solving a discrete logarithm problem. If a sufficiently powerful quantum computer were to emerge, it could, in theory, calculate your private key from your public key as soon as it is revealed, and thus sign transactions for you even before yours is confirmed. In this scenario, Bitcoin's security would be compromised for anyone who reused addresses or who delayed having their transactions included in a block.
Should we panic, though? Currently, existing quantum computers contain no more than a few hundred physical qubits, which are often unstable and subject to a multitude of errors. Breaking Bitcoin's ECDSA would require a stable, error-corrected computer with thousands, or even millions, of logical qubits. Experts estimate that such a feat remains decades away. The famous "quantum supremacy" feat announced by Google in 2019 involved only a specific calculation with no practical application, and since then, no major progress suggests that a quantum computer capable of breaking modern cryptography is imminent.
Bitcoin is not static. The protocol can evolve by consensus, through a soft fork or a hard fork. Post-quantum solutions are already being explored worldwide, including signatures based on hash functions or schemes using Euclidean networks, which are resistant to known quantum attacks. The real risk would not be the sudden emergence of a quantum computer, but rather the lack of community coordination to adopt an update in time that would secure the network against this new type of threat. Collective vigilance, responsiveness, and consensus will remain the keys to Bitcoin's resilience.
It's also worth remembering that, even if a quantum computer were able to break ECDSA, only bitcoins whose addresses have already revealed their public keys would be in immediate danger. Those remaining in unspent addresses would not expose any information to attack. Pending a hypothetical quantum computer, the best practice remains to avoid reusing addresses: each transaction should use a new address, a recommendation already valid today to preserve privacy and limit risks.
Bitcoin is a living system, an open-source protocol that has always adapted to challenges. While today's cryptography may become vulnerable tomorrow, the ecosystem has the capacity and collective intelligence to evolve and integrate post-quantum solutions when necessary. In the meantime, the threat of the quantum computer must be taken seriously and monitored closely, but it must not become a permanent bogeyman. Bitcoin's greatest weakness is not the quantum computer, but the idea that the network could not evolve in the face of it. Because as long as the community remains active and united, Bitcoin can remain a bulwark of individual freedom in a changing world.
👉 Also read: