Advances in quantum computing, like Google’s new Willow chip, could break the encryption that protects Bitcoin, warns Carlos Perez-Delgado, a lecturer at the University of Kent. He explained, “If I had a powerful quantum computer right now, I could take control of all Bitcoin.”
Bitcoin, which has reached record values of over $106,000, is at risk because quantum computers might one day crack the encryption that keeps its transactions secure. To prevent such an attack, Bitcoin would need a major update, which would be both expensive and time-consuming.
According to a study from the University of Kent, fixing Bitcoin’s encryption would require taking it offline for 76 days. This downtime could cost around $912 million, based on estimates that one hour of downtime costs $500,000. A less disruptive option would involve dedicating 25% of Bitcoin’s servers to the update while keeping the system running at a slower pace. However, this approach would take about 305 days—10 months—to complete.
Perez-Delgado emphasized how costly downtime can be, even for a short period. “Bringing your technology down, even for minutes or hours, is very expensive. For Bitcoin, the update could take weeks or months.”
The urgency comes from rapid progress in quantum technology. Google’s Willow chip, for example, can perform calculations in five minutes that would take today’s supercomputers 10 septillion years. While some experts see this as exciting progress, others are concerned about the risks it poses.
“If someone had a large quantum computer today, they could take control of Bitcoin, read private emails, and hack into computer accounts,” Perez-Delgado warned. “This is the reality of quantum computing’s potential.”
Perez-Delgado doesn’t mean to sound alarmist. IBM predicts we likely won’t have quantum computers big enough to threaten the current form of encryption anytime this decade, and its threat to cryptography remains hypothetical until then. But all tech entities are going to have to be proactive should it become a threat, Perez-Delgado warned.
“The indisputable fact that nobody can argue is that when we do get there, our current securities, the cybersecurity systems—which includes everything from Bitcoin to email—will be in great danger,” he said.
At the core of quantum computing’s threat to cryptocurrencies is its ability to perform exponentially more operations than classical computing. While classical computers use binary bits to perform actions one at a time, quantum computers use qubits, which can represent both the 0s and 1s that make up binary operations, allowing quantum computing to simultaneously perform functions classical computing would be able to fulfill only one at a time.
Today’s ubiquitous means of protecting information and transactions through public-private key encryption—essentially using a pair of different “keys” to lock and unlock data—are no match for powerful quantum computing, Perez-Delgado said. Instead, any technology using encrypted information will have to turn to “post-quantum,” or “quantum-safe,” cryptography.
For centralized companies like Google, this replacement could be as simple as asking users to download new software or to take down its server for an hour or a day to patch it with new cryptography programs. But for decentralized cryptocurrencies, implementing new encryptions is no cakewalk. With 275 million Bitcoin investors on a platform with no centralized authority, no one entity can introduce an update. It’s a quagmire for Bitcoin, which has attracted users expressly because it’s decentralized.
Moreover, the process of updating Bitcoin’s blockchain would involve updating each individual transaction. Combined with Bitcoin’s notoriety of being slow to process transactions, and you have an encryption undertaking that could move at a snail’s pace.
Perez-Delgado doesn’t see his research as “certain doom” for Bitcoin. The cryptocurrency has other options to handle a major update, including de-throttling, or speeding up, its block time, or time necessary to move or update transactions to the blockchain. But like the solution of implementing downtime to update the blockchain, speeding up the block time could come at the expense of the platform’s ability to handle user traffic.
“Those side effects are well worth the cost,” Perez-Delgado said.
This story was originally featured on Fortune.com
