Citi Warns Bitcoin Is More Vulnerable to Quantum Computing Attacks Than Ethereum

TLDR:

• Citi warns quantum computing could break Bitcoin encryption, with Q-Day set between 2030 and 2032.
• An estimated 6.7 to 7 million BTC in exposed wallets make Bitcoin a prime quantum attack target.
• Ethereum’s flexible governance positions it to adapt more readily against the quantum computing threat.
• Fireblocks CEO calls Bitcoin’s quantum risk a coordination issue and notes post-quantum tools exist.

Quantum computing poses a growing threat to the crypto sector, according to a new Citi research note. The report warns that Bitcoin faces far greater exposure than Ethereum.

That divide, analysts argue, comes down to governance rather than technology alone. Recent breakthroughs have pushed the estimated timeline for practical quantum attacks to as early as 2030.

With millions of Bitcoin already at risk, the industry is watching this closely. Analysts say the window for preparation is narrowing fast.

Bitcoin’s Structural Vulnerability to Quantum Attacks

Bitcoin transactions expose the sender’s public key to the network until they are confirmed. This creates a window where a quantum attacker could theoretically derive a private key.

From there, the attacker could redirect funds before the transaction is finalized. The exposure is brief but real, and it grows more dangerous as quantum computing hardware improves.

Google’s research suggests a 500,000-qubit machine could break Bitcoin’s encryption in minutes. No such machine currently exists, but the pace of progress is accelerating.

Google places its Q-Day estimate at 2032, while some researchers suggest 2030. Either way, the crypto industry has limited time to act.

The dormant wallet problem makes Bitcoin’s exposure more pressing. An estimated 6.7 to 7 million BTC sit in wallets with public keys already exposed. These wallets represent a concentrated and attractive target for any future quantum-capable actor.

Among those wallets, roughly 1 million Bitcoin believed to be mined by Satoshi Nakamoto remain untouched. These coins use early address formats that are particularly vulnerable to quantum attacks. At current prices, they carry an estimated value of around $82 billion.

Governance Gap Separates Bitcoin and Ethereum

Ethereum and other proof-of-stake networks are better positioned to adapt, Citi analysts said. Their more flexible governance allows for faster protocol changes when needed.

Ethereum also has a demonstrated history of regular protocol upgrades. That agility gives it a structural advantage against the quantum computing threat.

Bitcoin’s conservative, consensus-driven model is widely seen as central to its credibility. That same model, however, makes rapid protocol changes slow and contested.

Moving to quantum-resistant cryptography would likely require a hard fork, a notoriously difficult process. Broad network consensus would need to be achieved before any changes take effect.

Fireblocks CEO Michael Shaulov addressed this at the Financial Times Digital Asset Summit, arguing that the threat “is not actually a threat as people make it out to be.”

He described Bitcoin’s quantum challenge as “mostly a coordination issue” for the community rather than a technical one.

Shaulov further noted that “the entire internet industry needs to basically leapfrog and start using post-quantum encryption,” adding that “generally speaking, we have the available algorithm.” His remarks suggest that preparation, not the threat itself, remains the real challenge.

Citi’s analysts pointed to BIP-360 and BIP-361 as proposed Bitcoin upgrades worth monitoring. Ethereum, meanwhile, is not entirely immune to quantum threats either.

A quantum-enabled attacker could theoretically acquire enough private keys to control 33% of staked assets. This could allow disruption of block finality or broader network operations.

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