Quantum Threat Looms Over 6.9 Million BTC as Exposed Keys Leave Them Vulnerable

A recent study by Google Quantum AI found that approximately 6.9 million Bitcoin are at risk from quantum computers due to exposed public keys.

The study discovered that about a third of Bitcoin's circulating supply is held in addresses with publicly visible keys, leaving them vulnerable to offline quantum attacks.

Taproot addresses expose public keys by design, while P2PKH and other hashed address types store only the hash of the public key, making it difficult for a quantum computer to derive the private key. However, when a P2PKH or Taproot address is spent from, even once, the full public key is published on-chain.

Additionally, about 1.7 million Bitcoin are locked in lost Satoshi-era keys that cannot be migrated to quantum-safe addresses due to non-existent private keys. These coins are worth over $100 billion and pose a significant risk if a quantum computer is developed before they can be secured.