What would happen if quantum computers already cracked Bitcoin?

Author: Yohan Yun, Source: Cointelegraph, Compiled by: Shaw Jinse Finance

If a quantum computer capable of breaking modern encryption came online today, Bitcoin would likely be attacked—and no one would know.

"Everything would look like legitimate access," said David Carvalho, CEO of post-quantum infrastructure company Naoris Protocol.

"When you think you see a quantum computer, it's actually been controlling it for months."

"You wouldn't even know," he said.

Researchers at IBM, Google, and government-backed labs are racing to close the gap, but time is running out. The National Institute of Standards and Technology (NIST) has begun approving post-quantum algorithms, while most public blockchains still rely on cryptography designed in the 1980s.

For now, this is only a theoretical threat. But Carvalho warned that if the theory were to become a reality, Bitcoin's defenses would collapse rapidly, faster than the network could react. How a quantum attack could crack Bitcoin Bitcoin's core security depends on the Elliptic Curve Digital Signature Algorithm (ECDSA), a cryptographic standard first proposed in 1985. This system allows users to prove ownership using a private key, with only the corresponding public key visible to the network. Using Shor's algorithm, a sufficiently powerful quantum computer could theoretically recover the private key directly from the public key. This would allow an attacker to access any wallet whose public key has been made public on-chain, such as those used in early Bitcoin transactions. “It would be impossible to prove it was a quantum computer because it would have legitimate access,” Carvalho said. “You would just see those coins moving around as their owners decided to spend them.” Kapil Dhiman, CEO and founder of Quranium, a startup focused on post-quantum-secure layer-1 blockchains, warned that the earliest and most obvious victims would be the oldest wallets. He stated, "Satoshi's Bitcoins are like lambs to the slaughter. If these Bitcoins were to move, confidence in Bitcoin would collapse before the system even collapses." In this scenario, the blockchain would continue to process transactions normally. Blocks would be mined, and the ledger would remain intact, but ownership would quietly change hands. The reality today is that more powerful GPUs and more advanced algorithms have made brute-force cracking slightly more efficient. However, the ECDSA algorithm, which uses Bitcoin's 256-bit keys, remains far beyond the limits of conventional computing power. While banks, telecom networks, and government agencies are already testing post-quantum cryptography, most major blockchains still rely on technology from the 1980s. "All blockchains have identified this vulnerability as a root cause," said Diman, referring to the risk that current encryption methods like ECDSA could be cracked by quantum computers. Transitioning Bitcoin to a quantum-resistant model would require a complete overhaul of the network's consensus rules, which would require extensive coordination among miners, developers, and users. Researchers have already put forward several early proposals, including Bitcoin Improvement Proposal 360, which outlines a potential path to adopting new encryption schemes, and the "Post-Quantum Migration and Legacy Signature Sunset" proposal, which would phase out traditional signature schemes. Ethereum developers have also explored lattice-based signatures and other quantum-resistant schemes, but these have not yet been implemented. In traditional finance, this shift is already underway. The National Institute of Standards and Technology (NIST) has approved algorithms, and JPMorgan has partnered with Toshiba to test a quantum-safe blockchain. SWIFT has begun providing post-quantum security training for its network. "Traditional finance is actually leading the way," Carvalho said. "They have centralized control, a budget, and a single authority that can drive upgrades. Cryptocurrencies don't have that. Everything requires consensus." Some newer blockchain projects have positioned themselves as quantum-safe from the outset. The Naoris protocol, led by Carvalho, was mentioned in a separate proposal submitted to the SEC discussing post-quantum standards, while Diman's Quranium uses a NIST-approved stateless hash-based digital signature algorithm. Meanwhile, Quantum Resistant Ledger is a blockchain built on XMSS hash signatures, now a NIST-standardized algorithm. What if Bitcoin Fails the Quantum Test? For ordinary Bitcoin holders, the main concern is a sudden collapse in confidence, which could cause a price crash and spill over into traditional markets, where institutional adoption of cryptocurrencies is accelerating. "It's not zero chance that it has been leaked," Carvalho said. "But the consensus in the scientific, research and military communities is that it hasn't happened." During World War II, Nazi Germany used the Enigma cipher machine, which was considered unbreakable. But cryptanalysts led by Alan Turing and his Bletchley Park team secretly cracked it. The Allies kept the breakthrough secret so Germany could continue using the code. Carvalho warned: "By the time you think you see a quantum computer, it's already been in control for months." But experts remain optimistic that quantum-safe blockchain systems are achievable, and the industry is trying to align with standards already adopted in traditional finance. "Quantum-safe systems are possible," said Diman. "We just need to start building them before the threat becomes real." For now, quantum threats remain theoretical. Bitcoin's encryption technology remains strong, and computers capable of breaking it exist only on paper.