What does ‘cracking’ bitcoin in 9 minutes by quantum computers actually mean

Google’s Quantum AI team made headlines this week with the revelation that a future quantum computer could potentially derive a bitcoin private key from a public key in just nine minutes. This news caused a stir on social media and sent ripples through the markets, sparking concerns about the security of the cryptocurrency.

To understand the implications of this breakthrough, it’s important to first grasp how bitcoin transactions function. When you send bitcoin, your wallet uses a private key to sign the transaction, proving ownership of the coins. This process also generates a public key, which is a shareable address that is broadcast to the network and stored in the mempool, a waiting area for transactions to be confirmed by miners. On average, it takes about 10 minutes for a transaction to be included in a block and confirmed.

The security of bitcoin transactions relies on a mathematical problem known as the elliptic curve discrete logarithm problem, which links private keys and public keys. While classical computers struggle to reverse this math in a timely manner, a powerful quantum computer running an algorithm called Shor’s could potentially crack it.

The key aspect of the nine-minute timeframe mentioned in Google’s research lies in the pre-computation phase. The quantum computer can be primed in advance by pre-computing certain elements of the attack that are independent of the specific public key. Once the public key appears in the mempool, the quantum machine only needs around nine minutes to derive the private key. Given that the average confirmation time for bitcoin transactions is 10 minutes, this leaves a narrow window for an attacker to intercept the funds.

This scenario can be likened to a thief building a universal safe-cracking machine that only requires minor adjustments for each new safe encountered. The last step, which takes approximately nine minutes, is what allows the quantum computer to derive the private key and potentially redirect the funds before the original transaction is confirmed.

It’s important to note that the quantum computer required for such an attack does not currently exist. Google’s research estimates that a machine with fewer than 500,000 physical qubits would be needed, whereas the most advanced quantum processors today have around 1,000 qubits. However, the more immediate concern lies with the 6.9 million bitcoins, roughly one-third of the total supply, that are already vulnerable due to exposed public keys.

These coins are at risk of being compromised by a sufficiently powerful quantum computer, which could systematically crack exposed keys without time constraints. Additionally, the recent Taproot upgrade to the bitcoin network inadvertently expanded the pool of vulnerable wallets by making public keys visible on-chain by default.

While the bitcoin network itself would continue to function, the security model that underpins its value would be severely compromised if private keys could be derived from public keys. The solution lies in implementing post-quantum cryptography, which replaces the vulnerable algorithms with ones that quantum computers cannot crack. Ethereum has been working towards this migration for years, but bitcoin has yet to take steps in this direction.

In conclusion, the potential threat posed by quantum computers to bitcoin’s security underscores the need for proactive measures to safeguard the network and protect user funds from potential attacks in the future.