6.5 Million Bitcoins Vulnerable to Quantum Threats — Citi Warns
By John Nada·May 20, 2026·3 min read
Citi warns 6.5 million Bitcoins are exposed to quantum threats, urging investors to pay closer attention. Ethereum explores AI for security.
Quantum computing is fast becoming a formidable adversary for cryptocurrencies, especially Bitcoin, which Citi analysts highlight as being acutely exposed. Recent breakthroughs in quantum computing have accelerated potential threats to the cryptographic systems safeguarding not just cryptocurrencies but also broader financial networks and internet infrastructures, according to a report by the bank.
Bitcoin's vulnerability is particularly pronounced due to its conservative governance model, which slows down the implementation of protocol upgrades. Public keys exposed on-chain, dormant wallets, and early pay-to-public-key (P2PK) addresses pose a significant risk — with 6.5 to 6.9 million bitcoins potentially at risk, translating to about one-third of the circulating supply.
The cryptographic systems that protect cryptocurrencies like Bitcoin rely heavily on public-key cryptography, specifically the Elliptic Curve Digital Signature Algorithm (ECDSA). In theory, a quantum computer powerful enough could break ECDSA, enabling it to derive private keys from public keys, forge transactions, and potentially steal funds. Such a scenario underscores why Citi's report emphasizes the urgency of transitioning to post-quantum cryptography.
Still, the threat isn't immediate. Hardware capable of executing large-scale quantum attacks is believed to be years away. Experts suggest that blockchains will likely transition to post-quantum cryptography before such risks become reality. As Citi analyst Alex Saunders notes, this shortened horizon demands closer attention from investors.
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Yet contrasting views exist. While the pace of quantum computing progress is a concern, the leap to post-quantum cryptography could mitigate these risks. Saunders points to vulnerabilities tied to public keys exposed on-chain and highlights the importance of preemptive upgrades. But for now, Bitcoin's slow adaptability keeps it under the spotlight.
In the broader context of crypto security, Ethereum's Vitalik Buterin suggests a different approach. He sees AI-assisted formal verification as a future cornerstone for cybersecurity. By combining AI-generated code with mathematically verified software, Buterin believes the industry could counter growing fears of AI-accelerated vulnerabilities. Such technological advancements might just provide the edge needed to safeguard the crypto ecosystem.
Formal verification, which involves using machine-checkable mathematical proofs to ensure that software behaves exactly as intended, could specifically benefit Ethereum infrastructure, zero-knowledge proof systems, and post-quantum cryptography. This method has been around for decades, but advances in AI have made it more practical, enabling developers to write both code and the necessary proofs more efficiently.
Whether Bitcoin's inherent vulnerabilities or Ethereum's hopeful advancements prevail, the key takeaway is clear: the race against technological threats isn’t slowing down. And in this relentless tug-of-war, the battle for security remains as critical as ever.