From decrypt by Mat Di Salvo and Vince Dioquino

Google's announcement of its breakthrough Willow quantum processor has reignited debates about crypto security, with some observers suggesting quantum computers could break Bitcoin's encryption.

The tech giant claims its new quantum computing chip can complete certain calculations in five minutes, which would take traditional supercomputers an impractical amount of time to process. 

Quantum computing is a new type of computing that uses the strange properties of quantum physics, where small particles can exist in multiple states at once and affect each other instantly across distances to solve certain problems way faster than regular computers.

Unlike traditional computers that work with bits that are either 0 or 1, quantum computers use quantum bits (qubits) that can be both 0 and 1 at the same time, allowing them to process huge amounts of possibilities simultaneously.

Google claims that it has advanced quantum error correction, one of the first steps in making quantum computing practical.

Could it crack Bitcoin, then? 

Not yet, industry observers have pointed out. AllianceBernstein analysts said in a Tuesday report that the Willow chip—with 105 qubits—is still far from the several million qubits needed to overthrow the Bitcoin network. A qubit is the unit used to measure data in quantum computing. 

“Should Bitcoin contributors start preparing for the quantum future?” Bernstein analysts wrote. “Yes, but any practical threat to Bitcoin seems to remain decades away.”

Quantum computers, if sufficiently advanced, could theoretically break blockchains by using algorithms to crack cryptographic keys, weaken hash functions, and dominate mining, enabling theft, double-spending, and network control; however, these risks remain theoretical for now, and the blockchain industry is actively developing quantum-resistant solutions.

“Bitcoin contributors have also been debating a transition to quantum-resistant encryption,” the analysts added.

The Bitcoin network is currently the world’s most secure computing network—and has never been hacked. 

A hacker would have to take control of more than 50% of the Bitcoin network to comprise it. Doing so would require an absurd amount of computing power. 

Responding to Alphabet CEO Sundar Pichai's tweet announcing Google's chip breakthroughs, Ethereum co-founder Vitalik Buterin posed the following question: "What's the largest semiprime you can factor?"

Buterin's question is crucial for two reasons.

First, factoring large semiprimes (or numbers that are the product of exactly two prime numbers) is at the heart of breaking RSA cryptography, a standard widely used in secure communications and cryptosystems.

Second, the largest semiprime that can be factored by a computer chip, such as Google's Willow, represents a sort of "practical limit" to how it could break RSA encryption.

For traditional computers, this number sets a benchmark for what key sizes are currently secure. For quantum computers, tracking progress in semiprime factorization capabilities helps estimate when they become powerful enough to break commonly used RSA key sizes.

The relevance to quantum computing and blockchain security is direct:

Current RSA implementations typically use 2048-bit or 4096-bit keys. If quantum computers can factor semiprimes of those sizes, they could break those encryption systems.

Quantum resistance could be the answer

Buterin has extensively discussed the prospect of “quantum resistance” for cryptocurrencies and other blockchain-based applications.

According to Buterin’s blog post, quantum resistance for crypto use cases means designing cryptographic systems from the ground up while being aware of the threat from quantum computers.

In 2019, Buterin claimed that Google’s quantum supremacy was “no problem” for crypto.

"It's not true that quantum computers break all cryptography. They break some cryptographic algorithms,” he said at the time, adding that “for every cryptographic algorithm that quantum computers can break, we know that we have a replacement […] that quantum computers cannot break."

Though still technically years away, a quantum computer powerful enough to hack the Bitcoin network would be the least of anyone’s worries: if the most powerful computing network in the world could be compromised, just about any system on the planet could face the same threat.