Bitcoin Faces Greater Quantum Computing Risk Than Ethereum, Citi Warns

In brief

• Quantum computing advances are shortening the timeline for real attacks on crypto, with recent targets revised to 2030-2032.
• Bitcoin is more exposed than Ethereum, Citi researchers said, because fixing the problem requires a very challenging governance consensus.
• An estimated 6.7–7 million Bitcoin in dormant wallets sit with public keys already exposed, making them a prime target.

As quantum computing advances faster than expected, a fault line is emerging in the crypto world: Bitcoin may be significantly more vulnerable than Ethereum—and the difference has less to do with code than with politics.

In a research note published this week, Citi analysts warned that recent breakthroughs have shortened the timeline for practical quantum attacks on digital assets. Their conclusion is that not all blockchains will be equally prepared when that threat arrives.

Bitcoin's exposure is structural. Transactions expose the sender's public key to the network until confirmed, leaving a window during which a quantum attacker could theoretically derive a user's private key and redirect funds.

Google's recent research suggests a 500,000-qubit machine could break that encryption in minutes. Such a machine doesn't yet exist, but the analysts noted the estimates are continuously improving. Google’s Q-Day estimate—for when a quantum computer powerful enough to break current cryptography comes online—is 2032, but other researchers think it could happen as early as 2030.

The deeper problem is Bitcoin's governance. Transitioning to quantum-resistant cryptography would require broad consensus across the network, extensive testing, and likely a hard fork—a notoriously difficult process. Its conservative, consensus-driven model, central to Bitcoin's credibility, also makes rapid protocol changes slow and contested.

Ethereum and other proof-of-stake networks are better positioned, the analysts argued, thanks to more flexible governance and a history of regular protocol upgrades. That said, they are not immune: A quantum-enabled attacker could theoretically acquire enough private keys to control around 33% of a network's staked assets, enabling disruption of block finality or network operations.