What Is Q-Day? The Quantum Threat to Bitcoin Explained

Kripto dünyasındaki son gelişmelere göre, Price data by University Explainers Technology Guides What Is Q-Day? The Quantum Threat to Bitcoin Explained Experts warn quantum computers could someday forge Bitcoin’s digital signatures, allowing unauthorized transactions. By Jason Nelson Edited by Stephen Graves Apr 18, 2026 Apr 18, 2026 9 min read Create an account to save your articles.

Add on Google Add as your preferred source to see more of our stories on Google. In brief Today’s quantum computers are far too small and unstable to threaten real-world cryptography. Early Bitcoin wallets with exposed public keys are most at risk in the long term.

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Developers are exploring post-quantum signatures and potential migration paths. Quantum computers can’t break Bitcoin’s cryptography today, but new advances in the field suggest the gap is closing faster than expected. Progress toward fault-tolerant quantum systems raises the stakes for “ Q-Day ,” the moment when a sufficiently powerful machine could crack older Bitcoin addresses and expose more than $711 billion in vulnerable wallets .

Long seen as a distant threat on the horizon, Q-Day snapped into sharp focus in March 2026, with multiple research papers suggesting that quantum computers could break cryptographic systems sooner than expected . Upgrading Bitcoin to a post-quantum state will take years, which means the work has to begin long before the threat arrives. The challenge, experts say, is that no one knows when that will be, and the community has struggled to agree on how best to move forward with a plan.

This uncertainty has led to a lingering dread that a quantum computer that can attack Bitcoin may come online before the network is ready. In this article, we will look at the quantum threat to Bitcoin and what needs to change to make the number one blockchain ready. A successful attack would not look dramatic.

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A quantum-enabled thief would start by scanning the blockchain for any address that has ever revealed a public key . Old wallets, reused addresses, early miner outputs, and many dormant accounts fall into that category. The attacker copies a public key and runs it through a quantum computer using Shor’s algorithm .

Developed in 1994 by mathematician Peter Shor, the algorithm gives a quantum machine the ability to factor large numbers and solve the discrete logarithm problem far more efficiently than any classical computer. Bitcoin’s elliptic-curve signatures rely on the difficulty of those problems. With enough error-corrected qubits, a quantum computer could use Shor’s method to calculate the private key tied to the exposed public key.

As Justin Thaler, research partner at Andreessen Horowitz and associate professor at Georgetown University, told , once the private key is recovered, the attacker can move the coins. “What a quantum computer could do, and this is what’s relevant to Bitcoin, is forge the digital signatures Bitcoin uses today,” Thaler said.

Blockchain ekosistemindeki bu gelişme, dijital varlık piyasalarını şekillendirmeye devam ediyor. Uzmanlar, konunun yakın vadeli etkilerini mercek altına alıyor.