According to Citi's latest analysis, quantum computing advances are compressing the timeline for when machines could break Bitcoin's encryption. The bank now estimates a 34% probability of widespread encryption breaches by 2034, surging to 60-82% by 2044. The Citi Institute has been tracking quantum risk to financial systems throughout 2026, estimating that a quantum-enabled attack on a major US bank could put $2 to $3.3 trillion of GDP at risk, representing 10-17% of annual US GDP with potential for a six-month recession cascading from initial breach. The bank treats Q-day as a systemic event triggering contagion across global payment systems, interbank messaging, and digital identities, not contained within single sector contagion.
Citi identified 6.9 million BTC hold already-exposed keys, representing roughly one-third of circulating supply valued at around $500 billion at current prices. The vulnerability stems from older Bitcoin addresses using pay-to-public-key outputs that left public keys permanently visible, including wallets believed to belong to Bitcoin's pseudonymous creator Satoshi Nakamoto. The exposure breaks down into two categories: Satoshi Nakamoto's original holdings of approximately 1 million BTC that have never moved and remain in addresses where the public key is already published, and any Bitcoin spent from addresses since the 2021 Taproot upgrade that reveals its public key on-chain. Bitcoin's conservative governance structure makes protocol upgrades slow and difficult to coordinate, unlike proof-of-stake networks that upgrade more frequently.
According to the report, Google's quantum estimate cuts the timeline dramatically, requiring fewer than 500,000 physical qubits to crack Bitcoin's elliptic-curve cryptography, significantly below the millions figure often cited. The bank remains constructive on crypto's long-term ability to adapt through post-quantum cryptography, with BIP-360 and BIP-361 in development that propose quantum-resistant transactions and phased migration away from legacy signatures. However, these technical solutions exist but adoption remains voluntary and progress is glacial. The bank flagged a 'harvest now, decrypt later' risk, where attackers may already be collecting encrypted blockchain data today for future quantum-enabled decryption. Bitcoin currently trades around $76,900 as reported by crypto.news.
The warning highlights a stark strategic gap compared to competitors. Ethereum has a coordinated, well-funded post-quantum migration plan-Strawmap targets quantum resistance by 2030, while Bitcoin lacks a unified roadmap. Ripple has mapped a four-phase plan to make XRP Ledger quantum-proof by 2028. Bitcoin's anti-centralization culture, while a feature for many, becomes a liability when the network needs to coordinate urgent security upgrades before quantum hardware matures. The network that prides itself on immutability may face its most challenging upgrade in history, with the window for action now, not later. NIST's August 2024 standardization of post-quantum cryptography signals the starting gun for migration, creating clear regulatory and technical benchmarks for the industry.
