The emergence of quantum computers poses a significant threat to Bitcoin's security, with approximately 6.5 million tokens, valued at hundreds of billions of dollars, vulnerable to quantum attacks. The threat is no longer hypothetical, with Google's recent research suggesting that a sufficiently powerful quantum computer could crack Bitcoin's core cryptography in under nine minutes. This has prompted developers to consider various upgrades to build defenses against the potential threat.
Two primary ways a quantum machine could attack Bitcoin are through the long-exposure attack, targeting coins sitting idle on-chain, and the short-exposure attack, targeting coins in motion or transactions waiting in the memory pool. Several initiatives are underway to mitigate these threats, including BIP 360, which removes the public key permanently embedded on-chain, and SPHINCS+, a post-quantum signature scheme built on hash functions.
Other proposals, such as Tadge Dryja's Commit/reveal scheme and Hourglass V2, aim to protect transactions in the mempool and slow the spending of old coins, respectively. While these proposals are still in the development stage, they demonstrate the community's awareness of the issue and their efforts to address it.