What if Quantum Computers cracked Bitcoin Today?

If a quantum computer capable of breaking modern encryption were to come online today, Bitcoin would likely be under attack — and no one would know.

“Everything would look like legitimate access,” David Carvalho CEO of Naoris Protocol post-quantum Infrastructure Company told Cointelegraph. “When you think you’re seeing a quantum computer out there, it’s already been in control for months.”

“You wouldn’t even know,” He said.

IBM, Google, and other government-backed labs are collaborating with researchers to develop new technologies. racing to close that gapBut the clock ticks. NIST (National Institute of Standards and Technology) in the US has approved post-quantum encryption algorithms. However, most public blockchains are using old 1980s cryptography.

It’s still a hypothetical threat. Carvalho said that if this theory were to become reality, Bitcoin’s defenses could crumble much faster than it can react.

Bitcoin could be broken by a quantum attack

Bitcoin’s security is based on Elliptic Curve Digital Signature Algorithm (ECDSA), a cryptographic algorithm first introduced in 1985. It allows the user to verify ownership using their private key. Only the corresponding publicly visible key can be seen by the rest of the network.

Shor’s algorithm allows a powerful enough quantum computer to recover a secret key by comparing it with a public key. This would enable attackers to gain access to any wallet that has the public key exposed, like those in early Bitcoin.BTC) transactions.

“It would be impossible to prove a quantum computer did it because it derives legitimate access,” Carvalho said. “You’d just see those coins move as if their owners decided to spend them.”

Related: Bitcoin’s quantum countdown has already begun, Naoris CEO says

Kapil Dhiman, CEO and founder of Quranium — a layer-1 blockchain startup focused on post-quantum security — warned that the earliest and most visible victims would be the oldest wallets.

“Satoshi’s coins would be sitting ducks,” He told Cointelegraph. “If those coins move, confidence in Bitcoin will shatter long before the system itself fails.”

In this scenario, blockchain transactions would be processed as usual. The ledger and blocks would still be intact but the ownership of those blocks would have changed.

Today, brute force attacks are slightly more effective due to the use of better algorithms and more powerful GPUs. Classical computing is unable to handle ECDSA, even with Bitcoin’s keys of 256 bits.

Bitcoins is the main reason behind TradFi’s post-quantum encryption

Banks, telecommunication networks, and government agencies have already begun testing encryption based on post-quantum technologies. However, the majority of major blockchains are still using technology that dates back to the 1980s.

“All the blockchains have identified this vulnerability as a root cause,” Dhiman spoke of the danger that existing encryption methods such as ECDSA might be hacked by quantum computers.

The network consensus rules would have to be rewritten, requiring a broad level of cooperation among users, developers and miners.

Related: Lost your Bitcoin in California? You might get it all back

Early proposals have been floated by researchers, such as Bitcoin Improvement Proposal 360The document outlines possible pathways to adopting new cryptographic systems, as well as the “Post Quantum Migration and Legacy Signatures Sunset” Proposal to phase out existing signature schemes. Ethereum developers are also exploring lattice-based signatures Other quantum-resistant alternatives exist, although none of them has reached the implementation stage.

A shift has already begun in the traditional financial sector. US NIST approved algorithms and JPMorgan tested a blockchain that is quantum-safe in partnership with Toshiba. SWIFT now offers post-quantum training to its network.

“Traditional finance is actually ahead,” Carvalho said. “They have central control, budgets and a single authority that can push upgrades. Crypto doesn’t have that. Everything takes a consensus.”

Some of the newer projects in blockchain are positioning themselves from day one as being quantum-ready. Carvalho was the leader of Naoris, which is mentioned by an independent proposal submitted Dhiman’s Quranium, on the other hand, uses NIST-approved Stateless Hash-Based Digital Signature Algorithm. Quantum Resistant Ledger, meanwhile, is a Blockchain built on XMSS signatures based hashing, a NIST standard algorithm.

What happens when Bitcoin fails to pass the quantum test?

Bitcoin holders are most concerned about a sudden drop in confidence. This could lead to a price crash and cause ripples through markets that have been increasingly adopting cryptocurrencies.

“There is a non-zero probability of it being out now. The consensus in the scientific, research and military communities is that it is not the case,” Carvalho said.

“However, it would not be the first time world-class cryptography had been broken without public knowledge,” He added that he was referring to Enigma.

The Enigma code was used by Nazi Germany in World War II and it was thought to be unbreakable. Alan Turing, his team and other cryptanalysts from Bletchley park quietly broke it. To prevent Germany’s use of the cipher, the Allies kept their breakthrough secret.

“When you think you’re seeing a quantum computer, it’s already been in control for months,” Carvalho warned.

Experts remain confident that quantum-secure Blockchain systems will be achievable, and the industry has been trying to adopt standards that are already in place for traditional finance.

“Quantum-secure systems are possible,” Dhiman said “We just need to start building them before the threat becomes real.”

Quantum dangers are still theory for now. Bitcoin’s cryptography is strong and only paper computers are capable of cracking it.

Magazine: Bitcoin vs. the quantum computer threat: Timeline and solutions (2025–2035)