Can Quantum Computers Destroy Bitcoin? It will not be easy

One of the most overlooked issues with blockchain systems is their ability to withstand the rapidly evolving machines known as quantum computers.

These powerful computers use quantum physics to solve complex problems that are beyond the reach of traditional devices using qubits — an evolution of the binary bit. Qubits are able to represent the value 1 or 0 at the same time, promising to present an exponential increase in computational power.

The world’s major superpowers are allocating billions of dollars to developing this technology — and for good reason. The first nation or company to master quantum computing will be ready to decipher confidential documents from its adversaries.

In the case of blockchain systems, the encryption that protects your records from fraud may be at risk. In February, researchers at the University of Sussex estimated that a quantum computer with 1.9 billion qubits can crack the encryption that guarantees Bitcoin’s security in a mere ten minutes. Only 13 million qubits would be needed to crack the blockchain in just one day.

Fortunately, the ability to use quantum computers with so many qubits still seems to be years away. IBM introduced its 127-qubit processor in 2021, and a thousand-qubit unit cannot be finalized until 2023.

“We’re not there yet,” said Jens Groth, a Danish professor of cryptology and encryption and a researcher at Dfinity. “No one knows what the time horizon will be, but blockchains may not be in danger for ten or 20 years.”

Groth emphasizes that there is a distinction between the two types of qubits (physical and logical). A physical qubit achieves a superposition between 1 and 0 via a quantum gate. A logical qubit consists of nine physical qubits. “Company announcements about new qubit advancements are often related to physical rather than logical qubits,” he explains.

Advantage is for defenders

While researchers such as Groth do not consider quantum computers an immediate threat to blockchain technology, experimentation with solutions continues nonetheless. “Cryptographers think about what would be the most appropriate defensive measure,” he says.

Blockchain developers have a clear advantage in the race to fend off quantum power. More specifically, they can increase the number of digits in the cryptographic keys that secure the blockchain — a process that is easier to implement compared to advancing attackers. “Defenders are winning this battle in the long run,” says Groth.

This is evident in the field of symmetric key encryption by looking at the popular Advanced Encryption Standard (or AES). The most common variation of 128 keys can be deciphered by quantum computers and even traditional attackers.

However, AES variation 256, which has twice as many keys, seems strong enough to prevent brute force attacks by quantum computing machines in the near future.

However, some cryptographers avoid claiming that encryption is the automatic winner in a post-quantum world. “It is very difficult to predict whether we will be able to scale the size of keys against powerful quantum computers,” says Angshuman Karmakar, research partner in the Computational Security and Industrial Cryptography (or COSIC) group at KU Leuven University in Belgium.

“You always have to be pessimistic when you’re on the defensive side. A brilliant new algorithm can emerge and suddenly give attackers an advantage. The probability of this happening is extremely low, but it can never be disregarded”, explains Karkamar.

Meanwhile, network encryption (“lattice-based”) offers another possible solution to quantum attacks. This type of encryption adds mathematical noise that can confuse even a futuristic supercomputer.

“Quantum computers can find a needle in a haystack by constantly doubling the probability of finding it. You need to create structures that these computers cannot take advantage of,” explains Groth.

According to Karkamar, network solutions are under standardization process and should soon be ready for public use. “A lot will depend on how quickly the industry can implement new encryption. On the other hand, there is a lot of time left before quantum computers reach a level where they can decipher a blockchain”, he guarantees.

Migration to a new private key

Implementing an encryption upgrade for a blockchain system seems to be a big headache for cryptographers. On a traditional blockchain, like Bitcoin, each node will have to be convinced to switch to a new encryption method.

Governance protocols such as the Internet Computer can automatically update your system through user voting. Collective determination will be critical in all circumstances.

However, the process of updating existing private keys can create new vulnerabilities as, according to Groth, new keys will be generated by the system after successful implementation of post-quantum encryption. To activate a new key migration, users will have to sign an approval with their old key.

However, inactive users may never update their private key, which can lead to serious problems. Large inactive wallets, such as those containing around 1 million in BTC that are supposedly owned by Satoshi Nakamoto, will never undergo an encryption improvement.

This can make large parts of the crypto ecosystem prone to quantum attacks even if the blockchain they depend on is securely updated.

The moral of the story is that while blockchains now appear to be safe from quantum computing, developers will need to remain vigilant and ready to take further steps to ensure this remains true.

*Text written by Jeremy Van der Haegan, a freelance journalist covering business, politics, cryptocurrencies and blockchain technology in the Asia-Pacific region.

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