Europol warns 6.9 million bitcoin sit in wallets a quantum computer could one day crack

Europe's police agency has put a number on crypto's quantum problem. In a report published on Wednesday, October 7, Europol's European Cybercrime Centre said the main risk from future quantum computers lies in wallets whose public keys are already visible on the blockchain, not in the blockchains themselves, CoinDesk reported.

A powerful enough quantum computer could work out a private key from an exposed public key and spend the coins. About 6.9 million bitcoin sit at such addresses, including early payments and long-dormant holdings, the report said. Keys that are already exposed cannot be protected after the fact. The hash functions used in mining are far more resistant, according to the report.

Europol stressed that machines able to do this do not exist yet and did not predict when they will. "Cryptocurrencies will not collapse due to quantum computing," it said, describing adaptation as the most likely outcome.

The hard part is the move itself. A 2024 study cited in the report estimated that converting every bitcoin output to a quantum-resistant format would take at least 76 days of block space, or about 300 days if a quarter of each block were set aside. Europol urged developers, miners, exchanges and users to start a phased transition now.