Google Identifies Five Quantum Attack Paths Threatening Over $100 Billion in Ethereum Assets

Bitcoin, Ethereum and other major blockchains rely on elliptic-curve cryptography to authenticate transactions. A sufficiently capable quantum computer could derive private keys from public keys exposed onchain, allowing an attacker to sign valid transfers without breaching a wallet, device or exchange. That distinction matters because “Q-day” — when quantum machines can break standard public-key cryptography — may arrive without the conventional forensic evidence that normally identifies a security intrusion.

Christopher Smith, CEO and co-founder of Quantus Network, said on Aug. 10 that an initial attack could resemble scattered cases of lost or stolen keys. Targets may include Tether’s minting key rather than Satoshi Nakamoto’s Bitcoin holdings, valued at about $63 billion at the time. Google in March accelerated its post-quantum migration target to 2029, while Smith put the odds of cryptography-breaking capability emerging by 2028 at 50%.

Bitcoin transactions rely on elliptic-curve digital signatures. A sufficiently powerful quantum computer could use Shor's algorithm to derive a private key from a public key, leaving older addresses whose keys have already been exposed at greatest risk. A February 2026 estimate put nearly 7 million BTC at risk, including about 1 million attributed to Satoshi Nakamoto, with a combined value of about $440 billion. The issue has implications for holders' property rights and consensus across the network.

On June 13, 2026, an independent quantum computing advisory board convened by Coinbase said quantum computers could not yet break Bitcoin but urged immediate planning for quantum-resistant signatures. It estimated that about 6.7 million BTC was at risk but did not endorse freezing or restricting older coins. A May 6 report from Project Eleven set 2033 as its baseline year for Q-Day, with 2030 as the earliest scenario.

Bitcoin and Ethereum rely on elliptic-curve digital signatures to secure transactions and asset ownership. If quantum computers become substantially larger and more stable, they could theoretically derive private keys. The U.S. Commerce Department’s support for the quantum industry therefore has implications beyond technological competition and is adding pressure on the crypto sector to accelerate its adoption of post-quantum cryptography.

As of July 20, 2026, the U.S. Commerce Department planned to invest more than $2 billion in nine quantum-computing companies to help scale the technology. The development has renewed concerns about the security of Bitcoin and Ethereum. Experts are calling for prompt planning of Post-Quantum Cryptography upgrades and closer coordination among governments, regulators and developer communities.

Bitcoin transactions use elliptic-curve digital signatures to secure assets. A quantum computer running Shor’s algorithm could potentially derive private keys from public keys, putting older wallets and transaction security at risk. Ethereum, by contrast, has planned a mechanism allowing accounts to adopt quantum-resistant signatures, bringing corporate crypto treasury strategies and onchain governance capabilities into focus.

Google Quantum AI and other institutions published research on March 30, 2026, estimating that fewer than 500,000 physical qubits could crack a key in about nine minutes. Citi warned on May 18 that the potential attack timeline had shortened. Bit Digital had already announced on July 7, 2025, that it would sell about 280 Bitcoin and, alongside a $172 million fundraising, increase its holdings to 100,603 Ethereum.

Bitcoin uses elliptic-curve cryptography to protect assets and communications, but sufficiently powerful quantum computers could eventually break its current encryption. Experts say the more immediate danger is a “harvest now, decrypt later” strategy, in which attackers intercept and store large volumes of encrypted communications today, then recover sensitive historical data once the technology matures. The threat extends beyond wallet private keys.

Security experts and an early-stage venture investor have recently warned that historical communications and infrastructure data across the Bitcoin ecosystem may already be targets for quantum attacks. Ethereum has begun work on a post-quantum migration, but as of this report, neither Bitcoin nor related companies had publicly committed to specific safeguards, disclosed investment amounts or set completion dates. The upgrade timetable and division of responsibility therefore remain unclear.

Bitcoin and Ethereum rely on elliptic-curve cryptography to safeguard assets. A quantum computer capable of deriving a private key from a public key could potentially steal funds. Bitcoin activated Taproot on November 14, 2021, and because some transactions expose public keys in advance, the potential window for attack has widened.

The latest research from Google Quantum AI estimates that about 500,000 error-corrected physical qubits could be enough to crack a key within Bitcoin’s roughly nine-minute transaction confirmation window, far below previous estimates of several million qubits. No funds have been reported stolen through such an attack, but the researchers are urging the community to begin planning a migration to post-quantum cryptography.

Quantum computers could break Ethereum’s current elliptic-curve cryptography, threatening validator consensus, account signatures and onchain assets. Vitalik Buterin has identified four vulnerable areas in the protocol, including BLS signatures and KZG commitments. Upgrading Ethereum for quantum resistance is therefore critical to its long-term security and the protection of assets on the network.

Buterin has unveiled a comprehensive roadmap, while the Ethereum Foundation has formed a dedicated Post-Quantum team with the goal of completing protocol-level upgrades by 2029. The proposed measures include replacing vulnerable mechanisms with STARK proofs, introducing hash-based signatures into Lean consensus and exploring the use of SNARKs to reduce the performance burden of quantum-safe cryptography.