Google’s Quantum Artificial Intelligence team has suggested that the next generation of quantum computers planned to be developed will be able to reveal the private key of a Bitcoin wallet from its public key in just nine minutes. This prediction spread quickly on social media and caused concern in the markets.
The impact of quantum computers on Bitcoin
In Bitcoin, transactions are signed with a secret private key, and the public key corresponding to this key is transmitted to the network so that the transaction can be verified. Transactions published on the network remain in the queue in a waiting area called mempool until they are confirmed. While it currently takes an average of ten minutes for a transaction to be added to the blockchain, in the scenario mentioned in Google’s report, the private key can be detected in nine minutes with a quantum computer.
In order for quantum computers to produce solutions this quickly, certain calculations must be made beforehand. After completing the preliminary preparation phase, the attacker can complete the remaining steps and access the private key in nine minutes when the public key falls into the mempool. Since the average transaction confirmation time is around ten minutes, there is a possibility that attackers can manipulate the transaction and divert funds.
Bitcoin’s current security infrastructure is based on a mathematical problem that cannot be solved by classical computers. But a sufficiently powerful quantum machine will be capable of running complex algorithms that could shake this foundation.
Risks of public keys and current threats
The biggest risk is found in wallets whose historical and public keys are clearly displayed on the chain. The pay-to-public-key structure used in the early years of Bitcoin and wallets that reuse the same address permanently expose their public keys. In such cases, attackers are left in a position to launch a direct attack without depending on the instant transaction confirmation time.
Bitcoin Taproot update was shown as an additional risk factor by experts. Since the address structures have changed with Taproot, the public keys of more wallets on the chain are now directly visible. This increases the potential attack area.
While the most powerful quantum computers in today’s technology have a capacity of approximately one thousand physical qubits, it is stated that a machine with 500 thousand qubits will theoretically be required for a successful attack. In other words, it is not possible for such a threat to come to the fore immediately under current conditions.
Since block production in the network is based on the SHA-256 algorithm, quantum computers are not expected to provide a significant advantage in this section. So mining will be able to continue operating. However, private keys becoming more easily discoverable from the public key undermines Bitcoin’s core promise of reliability.
To deal with this problem, blockchain technologies need to transition to post-quantum cryptography methods. While the Ethereum front has been planning the transformation in this area for a long time, a similar preparation has not yet been brought to the agenda in Bitcoin.
