Quantum Computers Could Break Bitcoin by 2029: Latest Threat

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Recent advances in quantum computing have reignited a long-standing debate in the crypto world: could quantum computers break Bitcoin’s encryption by 2025–2029? Experts, developers, and major institutions are now openly warning that the threat is no longer theoretical, and that Bitcoin may need a major cryptographic upgrade within this decade to survive.

At the heart of the concern is Bitcoin’s reliance on elliptic curve cryptography (ECDSA) to secure wallets and transactions. While this system has held firm for over 16 years, a sufficiently powerful quantum computer running Shor’s algorithm could, in theory, derive private keys from public keys and steal funds. The question is no longer “if,” but “when” — and whether the Bitcoin community can act in time.

The quantum threat in plain terms

Bitcoin’s security rests on two main pillars: the SHA‑256 hash function that secures mining and the ECDSA digital signature scheme that protects wallets. Quantum computers do not break SHA‑256 in any practical way, but they do pose a serious threat to ECDSA and similar public‑key systems like RSA.

Classical computers would need billions of years to reverse‑engineer a Bitcoin private key from its public key. A large, error‑corrected quantum computer, however, could do this in hours or days using Shor’s algorithm. That means any Bitcoin address whose public key is visible on the blockchain becomes a potential target.

Not all Bitcoin is equally vulnerable. Funds in modern P2PKH and P2WPKH addresses are protected as long as the address is not reused. The real danger lies in early wallets, reused addresses, and certain script types where public keys are permanently exposed. Analysts estimate that several million BTC — worth hundreds of billions of dollars — sit in these quantum‑vulnerable formats.

Timeline: 2025–2029 window

Estimates of when a “cryptographically relevant” quantum computer (CRQC) might appear vary widely, but a growing number of experts now see a realistic risk window between 2025 and 2029. This shift is driven by rapid progress at companies like Google, IBM, and Microsoft, which are building larger, more stable quantum processors and demonstrating quantum advantage in specific tasks.

IBM, for example, has publicly targeted the launch of its first fault‑tolerant quantum system, IBM Quantum Starling, by 2029. Other roadmaps suggest that machines with thousands of logical qubits — enough to run Shor’s algorithm against 256‑bit elliptic curves — could emerge in the late 2020s. If these projections hold, Bitcoin’s current signature scheme could be at risk by the end of this decade.

Some researchers are more conservative, arguing that practical attacks are still 10–15 years away, possibly in the early 2030s. But even these longer timelines stress that preparation must begin now, because upgrading a decentralized network like Bitcoin takes years of coordination, testing, and adoption.

“Harvest now, decrypt later” and Q‑Day

Security agencies and cryptographers have long warned of a “harvest now, decrypt later” strategy: attackers collect encrypted data today (including blockchain transactions) and store it, waiting for quantum computers to mature before decrypting it. For Bitcoin, this means that transactions from 2009 onward could, in theory, be vulnerable decades later if the underlying cryptography is broken.

This concept has led to the term “Q‑Day” — the hypothetical moment when quantum computers can reliably break widely used public‑key cryptography. On Q‑Day, any address with a known public key becomes a target. Attackers could sweep funds from vulnerable wallets, potentially destabilizing markets and eroding trust in the network.

Because Bitcoin’s ledger is fully transparent and immutable, there is no way to “patch” old transactions. The only defense is to migrate funds to quantum‑resistant formats before Q‑Day arrives and to upgrade the protocol so that new transactions are secure against quantum attacks.

Bitcoin’s post‑quantum roadmap

Within the Bitcoin community, serious work is already underway to prepare for a post‑quantum world. A key effort is Bitcoin Improvement Proposal 360 (BIP‑360), which outlines a phased migration to post‑quantum cryptography using NIST‑standardized algorithms like ML‑DSA

The plan envisions a multi‑year transition: first introducing a quantum‑resistant address type (Pay‑to‑Quantum‑Resistant‑Hash), then gradually phasing out legacy ECDSA/Schnorr signatures. In later phases, the network could make old signature types invalid, effectively freezing any funds that have not been migrated to quantum‑safe formats.

Developers stress that this is not a quick fix. Integrating post‑quantum signatures into Bitcoin requires careful design to manage larger key and signature sizes, higher verification costs, and compatibility with existing infrastructure like the Lightning Network. The goal is a smooth, coordinated upgrade, not a rushed hard fork that could split the network.

What’s at stake for Bitcoin

The financial stakes are enormous. If a quantum computer successfully breaks ECDSA and starts stealing from exposed addresses, it could trigger a wave of panic selling, a collapse in confidence, and a potential loss of billions in market value. BlackRock, in its Bitcoin ETF filings, has explicitly flagged quantum computing as a material risk to Bitcoin’s long‑term security.

El Salvador, which holds over 6,000 BTC in its national reserve, has already taken steps to reduce quantum risk by redistributing its holdings across multiple addresses. Other large holders and institutions are quietly reviewing their custody strategies, including the use of post‑quantum‑ready hardware wallets and multi‑sig setups.

For ordinary users, the message is clear: avoid address reuse, use modern address formats, and keep an eye on wallet and exchange announcements about post‑quantum upgrades. Those with large holdings in early wallets should seriously consider moving funds to newer, more secure formats well before any Q‑Day scenario.

Industry and government response

Outside Bitcoin, governments and tech giants are already moving toward post‑quantum cryptography. The U.S. National Institute of Standards and Technology (NIST) has standardized several post‑quantum algorithms and recommends that organizations begin transitioning by 2030. The U.S. government has mandated that federal systems adopt post‑quantum standards by 2035.

Major tech companies, including Google, Cloudflare, and Apple, are already testing and deploying hybrid signature schemes that combine classical and post‑quantum cryptography. This “belt and braces” approach ensures that an attacker must break both systems to compromise security.

Bitcoin, as a decentralized, permissionless network, cannot simply flip a switch. But the broader trend is unmistakable: the digital world is preparing for a post‑quantum era, and Bitcoin must be part of that transition to remain credible and secure.

Is Bitcoin doomed by 2029?

Despite the alarming headlines, most experts do not believe Bitcoin is doomed by 2025–2029. The consensus among leading cryptographers is that Bitcoin still has a substantial window to adapt, provided the community acts with urgency and coordination.

Blockstream CEO Adam Back, a veteran cryptographer, has argued that a serious quantum threat to Bitcoin is more likely 20–40 years away, not within the next five years. He points out that today’s quantum computers are still noisy, error‑prone, and far from the millions of high‑quality qubits needed to break Bitcoin’s cryptography.

However, even skeptics agree that complacency is dangerous. The risk is not just that a quantum computer will appear tomorrow, but that the network will be unprepared when the time comes. The real threat to Bitcoin is not quantum computing itself, but the failure to upgrade in time.

What comes next

Over the next few years, the Bitcoin ecosystem is expected to see concrete steps toward quantum readiness. Wallet and hardware manufacturers are already building in support for post‑quantum signature schemes. Exchanges and custodians are reviewing their quantum risk exposure and updating their security policies.

On the protocol level, the debate will center on how and when to introduce quantum‑resistant signatures, how to handle legacy vulnerable funds, and how to balance security with decentralization and usability. These are not technical details; they are fundamental questions about Bitcoin’s governance and long‑term survival.

For investors and users, the takeaway is simple: stay informed, avoid known vulnerabilities, and support efforts to make Bitcoin quantum‑safe. The next few years will be critical in determining whether Bitcoin can evolve to meet the quantum challenge — or whether it becomes a cautionary tale of a system that was broken not by hackers, but by the march of technology.

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