Quantum

Bitcoin

ARK Invest, the investment firm led by Cathie Wood, says roughly 34.6% of the total&nbsp;<a href="https://bsc.news/post/what-is-bitcoin-how-it-works-mining-digital-gold-guide" rel="noopener noreferrer nofollow">Bitcoin</a> supply sits in address types that could be vulnerable to a future quantum computing attack. The remaining 65.4%, the firm argues, is already held in quantum-resistant formats. The findings come from a&nbsp;<a href="https://www.ark-invest.com/white-papers/bitcoin-and-quantum-computing" rel="noopener noreferrer nofollow">white paper</a> titled "Bitcoin And Quantum Computing," co-authored with Bitcoin-focused financial services company Unchained.
<h2 id="span-span-strong-what-exactly-is-at-risk-and-why-strong-span-span">What Exactly Is at Risk and Why?</h2>
The vulnerability is not theoretical noise. It comes down to how certain Bitcoin addresses work at a cryptographic level.
Bitcoin's security relies on two main pillars: elliptic curve cryptography (ECC), which protects private keys, and SHA-256 hashing, which secures the mining and transaction process. A sufficiently powerful quantum computer could, in theory, derive a private key from an exposed public key, allowing an attacker to steal funds from certain wallet types.
The white paper breaks down the at-risk supply as follows:
<ul>
 <li>Roughly 5 million BTC (25% of total supply) sits in reused addresses where public keys are already exposed on-chain, making them theoretically migratable but currently vulnerable</li>
 <li>Around 1.7 million BTC (8.6%) is believed to be permanently lost in P2PK (Pay-to-Public-Key) addresses, the earliest Bitcoin transaction format that locked funds directly to public keys rather than hashed addresses</li>
 <li>Approximately 200,000 BTC (1%) sits in P2TR (Pay-to-Taproot) addresses, which carry a specific key-path exposure</li>
</ul>
P2PK addresses are the oldest format on the Bitcoin network. Because they expose public keys directly, they represent a higher-risk category under a quantum threat model. Among those holdings, an estimated 1 million BTC is believed to belong to Satoshi Nakamoto, Bitcoin's pseudonymous creator.
<h2 id="span-span-strong-how-powerful-would-a-quantum-computer-need-to-be-to-actually-break-bitcoin-strong-span-span">How Powerful Would a Quantum Computer Need to Be to Actually Break Bitcoin?</h2>
This is where the timeline matters, and ARK's message is measured rather than alarming.
Current quantum computers operate in what researchers call the Noisy Intermediate-Scale Quantum (NISQ) era, running at around 100 logical qubits with shallow circuits. To crack Bitcoin's ECC, a machine would need approximately 2,330 logical qubits and tens of millions to billions of quantum gate operations. That gap is enormous.
"Today's quantum systems lack the capabilities required to compromise Bitcoin," wrote the paper's authors, Dhruv Bansal of Unchained, Tom Honzik of Unchained, and David Puell of ARK Invest.
The report also notes that even if quantum systems eventually reach that level, any major breakthrough would almost certainly disrupt broader internet security first. It means banks, governments, and technology infrastructure would face pressure to respond well before Bitcoin becomes the primary target, giving the network time to adapt.
For context, Chicago-based PsiQuantum is&nbsp;<a href="https://www.psiquantum.com/news-import/psiquantum-breaks-ground-chicago" rel="noopener noreferrer nofollow">building</a> a facility targeting one million physical qubits, with completion expected in 2027. The company raised $1 billion from BlackRock-linked funds. Even that machine would fall well short of what is needed to break Bitcoin's cryptography in real time.
<h2 id="span-span-strong-is-this-an-immediate-threat-or-a-long-term-risk-strong-span-span">Is This an Immediate Threat or a Long-Term Risk?</h2>
Quantum computing is a long-term structural risk, not an imminent crisis.
The firm outlines five stages of quantum computing advancement. Bitcoin held in vulnerable addresses should not face material risk until at least stage three, when a quantum machine could break a 256-bit ECC key. Only at stage five, the final stage, would a quantum computer be capable of breaking ECC faster than Bitcoin's 10-minute block time.
<h3 id="span-span-strong-why-there-will-be-warning-signs-before-a-crisis-strong-span-span">Why There Will Be Warning Signs Before a Crisis</h3>
Rather than a sudden "Q-Day" scenario, ARK expects the progression to unfold gradually, with many intermediate signals along the way. That view contrasts with more alarmist takes. Earlier this year, Christopher Wood, a portfolio strategist at Jefferies, advised investors to cut 10% of their Bitcoin allocation and shift into gold specifically because of quantum risk, a move that rattled parts of the market.
ARK Invest’s report argues that the Bitcoin community will have time to deploy quantum-resistant upgrades before any machine reaches the capability threshold needed to cause real damage.
<h3 id="span-span-strong-what-would-a-quantum-safe-bitcoin-look-like-strong-span-span">What Would a Quantum-Safe Bitcoin Look Like?</h3>
Protecting Bitcoin against quantum attacks would require integrating post-quantum cryptography (PQC) into the protocol. The white paper points to two specific schemes: ML-DSA, a lattice-based signature method, and SLH-DSA, a hash-based signature method. Both are recognized standards that give researchers confidence in PQC's technical foundation.
One proposal currently under discussion is BIP-360, which would introduce a Pay-to-Merkle-Root output type. This format would reduce long-exposure quantum risk by removing Taproot's key-path vulnerability. However, Chris Tam, president and head of quantum innovation at BTQ Technologies, has noted that BIP-360 alone is not a complete solution.
Implementing PQC at the consensus level is also not straightforward. Bitcoin's decentralized governance structure means any protocol change requires broad agreement across the network, typically through a soft fork supported by the majority of participants.
<h2 id="span-span-strong-how-does-ark-s-estimate-compare-to-other-research-strong-span-span">How Does ARK's Estimate Compare to Other Research?</h2>
Not all analysts see the risk the same way. A February analysis by CoinShares put the realistically market-relevant quantum-vulnerable Bitcoin at around 10,200 BTC, or roughly 0.05% of supply. That figure accounts for practical attack conditions rather than theoretical address exposure.
ARK's 35% figure captures the broader theoretical surface area, including coins that could be migrated before any attack becomes viable. The two estimates are not necessarily contradictory. They measure different things: one reflects what an attacker could realistically target today, the other reflects the total supply that would need to be addressed over time.
<h2 id="span-span-strong-conclusion-strong-span-span">Conclusion</h2>
ARK Invest's white paper does not argue that Bitcoin is broken or about to break. It argues that a sizable portion of the supply, mostly in older and reused address formats, carries structural tail risk that will need to be addressed before quantum computing matures.&nbsp;
The 65.4% of supply already in quantum-resistant addresses shows the network is not starting from zero. The technical path forward, through post-quantum cryptographic standards and protocol upgrades, exists. The harder challenge is coordinating a decentralized network to execute those upgrades well before the math makes inaction costly.
<h2 id="span-span-resources-span-span">Resources</h2>
<ol>
 <li><a href="https://www.ark-invest.com/white-papers/bitcoin-and-quantum-computing" rel="noopener noreferrer nofollow">Report by Ark Invest</a>: Bitcoin And Quantum Computing</li>
 <li><a href="https://www.thestreet.com/crypto/technology/cathie-woods-ark-warns-of-shocking-risk-to-35-bitcoin" rel="noopener noreferrer nofollow">Report by The Street</a>: Cathie Wood's ARK warns of shocking risk to 35% of Bitcoin</li>
 <li><a href="https://www.coindesk.com/tech/2026/03/12/cathie-wood-s-ark-invest-says-quantum-computing-is-a-long-term-risk-for-bitcoin-not-an-imminent-threat" rel="noopener noreferrer nofollow">Report by CoinDesk</a>: Cathie Wood's Ark Invest says quantum computing is a long-term risk for bitcoin, not an imminent threat</li>
 <li><a href="https://www.psiquantum.com/news-import/psiquantum-breaks-ground-chicago" rel="noopener noreferrer nofollow">Article by PsiQuantum</a>: PsiQuantum Breaks Ground on America’s Largest Quantum Computing Project in Chicago</li>
</ol>

Cathie Wood’s ARK Invest Warns Quantum Might Break the Internet Before It Breaks Bitcoin

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