Citi Research Warns Bitcoin May Be More Exposed to Quantum Threats Than Ethereum
Citibank has published research suggesting progress in quantum computing is advancing faster than previously expected, potentially accelerating the window for real-world attacks on crypto assets, CoinDesk reported.
The bank's analysts argue that Bitcoin carries greater exposure than Ethereum, driven not only by differences in cryptographic implementation but also by the pace and mechanics of protocol upgrades. Recent academic and industry work is also pulling forward estimates for "Q-Day"—the point at which quantum machines could break widely used cryptographic systems.
Citi referenced Google research indicating that a system with roughly 500,000 qubits could, in theory, crack relevant encryption in minutes. Such hardware does not yet exist, but Citi said outside projections are steadily improving. Google has cited 2032 as a potential timeframe, while some researchers place the risk as early as 2030.
The report highlighted a structural vulnerability in Bitcoin: once a user broadcasts a transaction, the sender's public key can be revealed on the network before confirmation. In that window, a sufficiently capable attacker could theoretically derive the private key and divert funds.
Citi also emphasized that mitigating the threat would be harder for Bitcoin than for some other networks. Moving to quantum-resistant cryptography would likely require broad consensus, extensive testing and potentially a hard fork. The bank said Bitcoin's conservative, consensus-driven governance model supports credibility but can slow protocol changes.
Citi estimated that about 6.7 million to 7 million BTC sit in dormant wallets with exposed public keys, creating a concentrated set of potential targets. The report noted the widely held view that roughly 1 million bitcoins mined by Satoshi Nakamoto in Bitcoin's early days have never moved and use an older address format. At current prices, that tranche is estimated at around $82 billion.
By contrast, Citi said Ethereum and other proof-of-stake networks may be better positioned to respond because of more flexible governance and a consistent long-term cadence of upgrades. The bank cautioned that this does not make them immune. Analysts said that if attackers used quantum capabilities to obtain enough private keys, they could theoretically control about 33% of staked assets, potentially disrupting block finality or impairing network operations.
For Bitcoin, Citigroup singled out BIP360 and BIP361 as proposals to watch for progress toward quantum resistance. Citi's central takeaway is that long-term resilience will depend less on today's design choices than on a network's ability to adapt quickly.
The report echoes comments made last week by Fireblocks CEO Michael Shaulov at the Financial Times Digital Assets Summit in the UK. Shaulov said Bitcoin's quantum challenge is primarily a community-coordination issue, not only a technical one.
