Last year, tech giant Google announced a breakthrough with the launch of its "Willow" chip. The computing power of its quantum computer is exponentially greater than that of a conventional supercomputer, raising concerns about the security of Bitcoin and blockchain technology.
Quantum computers perform complex calculations by leveraging the principles of quantum mechanics. This allows them to solve certain tasks such as optimization, cryptography, and simulations much faster than classical computers. According to Google, its Willow chip can solve complex problems in less than five minutes-problems that would take a supercomputer around 10 quadrillion years. However, the risk to Bitcoin is lower than some skeptics might think.
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Bitcoin wallets remain secure against quantum computing
Bitcoin uses the cryptographic hash function SHA-256 to secure transactions and generate new blocks by solving complex mathematical puzzles. Many other systems-such as SSL certificates and secure data storage-also rely on this function for encryption. Quantum computers could threaten the security of SHA-256 by breaking the underlying cryptographic algorithms. This would allow a quantum computer to crack the private key of a Bitcoin address. Satoshi Nakamoto’s wallet, holding over one million Bitcoin (worth 105 billion USD at today’s price), would be a prime target.
On the one hand, current quantum computers are nowhere near powerful enough to break Bitcoin’s encryption. The computing power of this technology is measured in quantum bits, or “qubits.” Estimates suggest that over 13 million qubits would be required to pose a threat to Bitcoin wallets. For comparison, Google’s Willow chip achieves fewer than 105 qubits. Furthermore, Bitcoin can defend itself by transitioning the blockchain to quantum-resistant cryptographic algorithms. Researchers have already developed such methods.
Threat to Bitcoin mining
Quantum computers would pose a threat to mining if they could solve proof-of-work puzzles exponentially faster than classical miners. This could lead to a 51% attack, in which a single entity controls the majority of mining power. In such a scenario, the quantum computer could change the network’s rules and enrich itself.
Although powerful quantum computers could theoretically solve the puzzles much faster than traditional machines, several factors mitigate this threat. First, quantum computing performance is expected to improve gradually due to the technical challenges of scaling up qubit counts and implementing robust error correction.
As the first quantum computers enter the market, the impact of any new machine will be diluted. Every quantum computer that joins mining increases overall competition and computational demand. In addition, today’s quantum computers only run for a few seconds. Extending this runtime requires advanced error correction techniques and millions more qubits. This limits the immediate threat to Bitcoin-at least until quantum-resistant mechanisms are implemented.
Malicious actors have other targets
Attackers with access to a quantum computer are likely to target systems with more immediate value long before attacking SHA-256 blockchains like Bitcoin-such as the far simpler cracking of RSA encryption. RSA is used in secure communication, banking, and government data. Anyone storing their wealth in a bank instead of Bitcoin is also at risk from quantum computers.
Malicious actors could also exploit vulnerabilities in critical infrastructure or steal sensitive corporate information. These targets are far more likely to be prioritized due to their broader economic and strategic implications than Bitcoin. Nevertheless, raising awareness within the blockchain community remains important. Transitioning to quantum-resistant algorithms is theoretically easy to implement, but it requires a clear consensus. If that consensus is reached too late, short-term complications could arise.
