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.
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.
