A quantum computer on display at the World Manufacturing Convention in Heifei, China, in September 2025.
Photo: AFP/ Fang Dongxu
Google has issued a wake-up call to the Bitcoin community to take urgent action to upgrade blockchain security as advances in quantum technology increase the risk of fraudulent transactions and theft.
Google recently published a white paper warning that quantum computers were already technically capable of intercepting and stealing Bitcoin during an active transaction.
University of Auckland professor of mathematics Steven Galbraith (an associate member of New Zealand’s Dodd-Walls Centre for Photonic and Quantum Technologies) said the risk was real but not immediate.
“There is no evidence that anyone has a quantum computer that can do anything right now,” he said.
Why the urgency?
While the risk might not be immediate, bad actors were already harvesting dormant assets, to decrypt later.
“So if someone’s interested in your medical data, they can harvest it now by just monitoring what’s being sent over the Internet, and then they can just store that on hard disk,” Galbraith said.
“And then whenever they get a quantum computer in the future, they will be able to decrypt that. And so that’s one of the reasons why people are being encouraged to start switching to the post-quantum cryptography (PQC).
Why Bitcoin’s blockchain is at particular risk
Nobel-prize winning physicist John Martinis who helped build Google’s quantum computers said the research showing how a quantum computer could break Bitcoin encryption in minutes should be taken seriously.
While there was an industry solution to protect data using PQC, it was expected to take years to fully implement and upgrade vulnerable assets, though about 20 percent of internet traffic was already protected.
Galbraith said systems that were regularly upgraded by big tech and banks were moving in the right direction, but legacy systems, which did not receive regular security updates, such as Bitcoin’s blockchain, were at risk.
While the white paper was calling for the Bitcoin community to take urgent action to upgrade blockchain security, Galbraith said the nature of the Bitcoin community would make that difficult as there was no central organisation in place to upgrade the system to latest best practice.
The Bitcoin blockchain is decentralised global network and maintained by volunteers, with changes made by a consensus of participants.
Cryptocurrency NZ co-founder Nicolas Turnbull said the Bitcoin community was leaderless by design, though steps were being taken to modernise the system.
In the meantime, he said it was important for community members to upgrade Bitcoin wallets to the latest standard, which could be scaled-up to protect against a quantum-based attack.
However, upgraded wallets wouldn’t address the risk to dormant assets and transactions.
Treasure hunters and hackers
The white paper indicates Bitcoin transactions were at “immediate risk” because they took an average ten minutes to complete, giving a hacker with a quantum computer plenty of time to steal the Bitcoin asset as it moved from one wallet to another.
Furthermore, the paper says Bitcoin assets, which had been locked-in for various reasons, such as lost keys, were particularly vulnerable as they couldn’t be migrated via standard software updates.
“1.7 million Bitcoin have not been transacted since 2009 despite the fact that such coins are known to be vulnerable to at-rest quantum attacks,” the paper says.
“They represent a fixed, multibillion-dollar target that will inevitably become accessible to a quantum actor.”
Dormant Bitcoin stashes included a treasure chest of 1 million Bitcoin, believed to have been owned by the mysterious Bitcoin inventor Satoshi Nakamoto.
Turnbull said anyone who succeeded in gaining access to 1.7 million Bitcoin, would potentially crash the market.
“You are going to tank the price,” he said, though there would be plenty of people looking to capitalise on the buying opportunity.
“I know I’d be buying up as much as I can.”
Still, it would be difficult to cash-out a treasure chest of Bitcoin.
“You’d have a pretty big target on your back if you were to essentially get into that (Satoshi Nakamoto) wallet. I reckon it would be the most watched wallet out there,” Turnbull said.
Cybersecurity risks loom for Bitcoin investors
The Google paper says the transition to PQC would take time and should begin now.
“We contend that the amount of time remaining before the arrival of cryptographically relevant quantum computers (CRQCs) still exceeds the amount of time needed to migrate public blockchains to PQC, though the margin for error is increasingly narrow,” the report says.
“Therefore, we … urge all vulnerable cryptocurrency communities to begin PQC transition immediately while its timely completion is still the likely prospect.”
Galbraith said investors need to be aware of the risk.
“I’m not the person to ask investment advice, but certainly the technical person. It’s absolutely an extremely high risk investment, I’d say.”
Sign up for Ngā Pitopito Kōrero, a daily newsletter curated by our editors and delivered straight to your inbox every weekday.