Could Quantum Computers Defeat Bitcoin? Not So Fast. – Decrypt

One of the most overlooked problems of blockchain systems is their ability to resist the rapidly evolving machines known as quantum computers.

These powerful computers use quantum physics to solve complex problems that are beyond the reach of conventional tools, using qubits – an evolution of the classic binary bit. Qubits are capable of representing the value 1 or 0 at the same time, which promises to deliver an exponential increase in computing power.

The world’s top superpowers are pouring billions of dollars into the development of this technology, and for good reason. The first country or company to use quantum computing would be ready to crack the encryption protecting sensitive documents from rivals.

In the case of blockchain systems, the cryptography protecting their tamper-proof ledgers could be at risk. Researchers at the University of Sussex estimated in February that a quantum computer with 1.9 billion qubits could crack the encryption that protects bitcoin in essentially just 10 minutes. Only 13 million qubits could do the job in about a day.

Fortunately, the ability to deploy quantum computers with so many qubits is still many years away. IBM only unveiled its 127-qubit processor last year, while a 1,000-qubit unit is set to be completed by the end of 2023.

“We are not there yet,” said Danish professor Jens Groth in cryptology and encryption researcher at Dfinity. “No one knows what the exact time frame will look like, but the blockchain could be at risk in just 10 to 20 years.”

Groth underscores that there is an important difference between the two types of qubits—the physical and the logical ones. The latter describes an orbit that achieves a superposition between 1 and 0 through a quantum gate. A logical qubit consists of nine physical qubits. “The company’s announcements about a novel qubit milestone usually concern physical qubits, not logical ones,” he explains.

defenders have the upper hand

Although researchers such as Groth do not classify quantum computers as an immediate threat to blockchain technology, experimentation with solutions continues. “Cryptographers reflect on what a suitable countermeasure would look like,” Groth says.

Blockchain developers have a clear advantage in the race to hedge against increasing computing power. Specifically, they can increase the number of digits in the cryptographic keys that protect the chain—a process that is fast for attackers to scale up to capture. “The defenders are winning this battle in the long run,” Groth claims.

This is evident in the area of ​​symmetric key encryption when examining the popular Advanced Encryption Standard (AES). The most common variation of 128 keys can be cracked by quantum computers and even classic attackers. However, the AES 256 variation, featuring twice the amount of keys, appears strong enough to prevent brute force attacks by quantum machines for the foreseeable future.

Some cryptographers, however, are cautious about considering encryption as the automatic winner in the post-quantum world. “It is very hard to predict whether we will manage a consistent critical size against powerful quantum computers,” says Angshuman Karmakar, a research associate at KU Leuven’s Computer Security and Industrial Cryptography Group (COSIC).

“You always have to take a pessimistic approach when you’re on the defensive. A great new algorithm can pop up and suddenly put attackers at an advantage. The chances of this happening are extremely small, but never rule it out.” Can be done,” says Karmakar.

Meanwhile, lattice-based cryptography offers another potential solution to quantum attacks. This type of encryption adds mathematical noise that can confuse even future supercomputers. “Quantum computers can find a needle in a haystack by consistently doubling the probability of finding it. You need to design structures that these computers cannot take advantage of,” Groth says.

According to Karmakar, lattice-based solutions are currently in the process of standardization and should be ready for public use soon. “A lot will depend on how fast the industry can implement the new encryption. On the other hand, there is a lot of time left for quantum computers to reach the level where they can crack blockchains,” he says.

switching to a new private key

Implementing encryption upgrades for blockchain systems seems to be the biggest headache for cryptographers. In a typical blockchain like bitcoin, each node has to be convinced to switch to a new encryption method. Governance protocol users such as Internet computers can automatically update their systems through voting. Collective resolution will be necessary in all cases.

However, the process of upgrading existing private keys can create new vulnerabilities. This is because, according to Groth, the new key will be generated by the system once post-quantum encryption is successfully implemented. To activate the switch to the new key, users must sign for approval with their old one.

However, inactive users may never upgrade their private keys, which can lead to serious problems. The sizable inactive wallet containing about 1 million bitcoins believed to belong to Satoshi Nakamoto will likely never see an encryption increase. This could leave some legacy parts of the crypto ecosystem open to quantum-based attacks, even if the blockchain they rely on has been securely upgraded.

The bottom line is, while blockchains are safe from quantum computing for now, developers will need to be vigilant and ready to take new steps to ensure this.

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