About 7.12 million Bitcoin, representing 35.4% of the total supply in existence, currently has exposed public keys visible on Bitcoin's blockchain, according to data from analytics firm Glassnode. While today's computers cannot exploit this exposure, a large enough quantum computer could theoretically use this information to access the coins.
A public key functions like a lock that anyone can study on the public ledger. For most holders with exposed coins, the risk can be eliminated in minutes by moving Bitcoin to fresh addresses that have not yet revealed their public keys.
Breakdown of Exposed Supply
Glassnode's analysis identifies two main categories of exposure. Address reuse accounts for 25.8% of exposed supply, while cryptocurrency exchanges hold 11.6% of all Bitcoin in exposed addresses.
Among major exchanges, Robinhood holds 100% of its Bitcoin in exposed addresses, Binance holds 85%, and Coinbase holds approximately 5%, according to Glassnode's entity data. The firm notes these figures are not security ratings. US government Bitcoin holdings show no exposure.
Coinbase, which provides custody for most US spot Bitcoin ETFs, has begun work on upgrading its systems. In October, Coinbase's CEO stated that the company had begun the process to upgrade its custody to be post-quantum secure.
The Satoshi Question
Approximately 1 million Bitcoin linked to early addresses associated with Satoshi Nakamoto remain unmoved after more than 15 years. Unlike other exposed coins, these cannot be easily remedied without a transaction from the original holder.
Two separate proposals have emerged regarding these coins. A draft proposal from Casa's Jameson Lopp would freeze coins that never upgrade to post-quantum security, while Blockstream CEO Adam Back favors optional upgrade paths. Neither proposal currently has an activation date.
Timeline of the Quantum Threat
In March, Google reported that a quantum computer with fewer than 500,000 qubits could break current encryption methods in minutes. No such machine currently exists. Adam Back has suggested a quantum computer capable of threatening Bitcoin security could emerge within 20 to 40 years.
At current market prices, the exposed Bitcoin supply is valued at more than $500 billion. However, some analysts have suggested significantly lower figures for coins likely to be targeted. CoinShares estimated only about 10,200 BTC would represent a meaningful target for actual market impact.
In October, Nasdaq-listed Next Technology Holding approved selling or pledging approximately 5,833 Bitcoin, citing quantum computing among the reasons for the decision.
