A quantum computer could potentially derive a bitcoin private key from a public key in approximately nine minutes, according to Google's Quantum AI team. This revelation has sent shockwaves across social media and the markets, but what does it really mean in practical terms?
To grasp the implications, it's essential to understand how bitcoin transactions work. When a bitcoin transaction is made, the wallet uses a private key to sign the transaction, which is a secret number that verifies ownership of the coins.
This signature also reveals the public key, a shareable address that is broadcast to the network and stored in the mempool until a miner includes it in a block, a process that takes around 10 minutes on average. The private and public keys are linked by a complex mathematical problem known as the elliptic curve discrete logarithm problem, which classical computers cannot reverse in a useful timeframe.
However, a sufficiently powerful future quantum computer using an algorithm called Shor's could potentially reverse this math. The nine-minute timeline comes into play when a quantum computer is 'primed' in advance by pre-computing the parts of the attack that don't depend on any specific public key.
Once the public key appears in the mempool, the machine only needs about nine minutes to derive the private key, giving the attacker a roughly 41% chance of redirecting funds before the original transaction confirms. This is akin to a thief building a universal safe-cracking machine that works for any safe, requiring only a few final adjustments once a new safe appears. The more pressing concern is the 6.9 million bitcoin that already sit in wallets with exposed public keys, including early bitcoin addresses and wallets that have reused addresses. These coins are vulnerable to attack without the need for the nine-minute race, as an attacker with a sufficiently powerful quantum computer could crack them at leisure.
The bitcoin network itself would continue to function, but the ability to derive private keys from public keys would undermine the ownership guarantees that make bitcoin valuable, putting anyone with exposed keys at risk of theft and potentially collapsing institutional trust in the network's security model. The solution lies in post-quantum cryptography, which involves replacing the vulnerable math with algorithms that quantum computers can't crack, a migration that Ethereum has been working towards for eight years, but bitcoin has yet to initiate.