Bitcoin now has a quantum computing escape route, but 7 million BTC may still be exposed

Bitcoin researchers demonstrated a quantum‑resistant transaction on the mainnet, showing that some users can move funds away from future quantum threats without waiting for a protocol upgrade. The transaction, executed on August 26, used a construction that replaces elliptic‑curve signatures with a hash‑based security model.

How the quantum‑safe transaction works

The method, called Quantum‑Safe Bitcoin (QSB), leverages the fact that most Bitcoin addresses keep the public key hidden behind a hash until the address is spent. By repeatedly adjusting transaction data until a hash matches Bitcoin’s signature format, the transaction can be signed without revealing a public key. This shifts the security assumption from elliptic‑curve cryptography, which is vulnerable to Shor’s algorithm, to the difficulty of reversing hash functions, which quantum computers can only accelerate modestly.

Limitations and practical challenges

While the transaction is valid under Bitcoin’s consensus rules, it is non‑standard and does not propagate through the public mempool. StarkWare had to submit it directly to miner MARA via the Slipstream service. The computational effort required several hundred dollars, with estimates of $75‑$150 for cloud‑GPU search phases, making the approach unsuitable for everyday wallet use.

Remaining exposure

Approximately 7 million BTC remain at risk because their public keys are already exposed through older address formats, Taproot outputs, or address reuse. QSB does not provide a migration path for these coins, leaving a significant portion of Bitcoin vulnerable to future quantum attacks.

Industry response

In July, a consortium of institutions—including BlackRock, Coinbase, and Strategy—committed $15 million over three years to Bitcoin security research, covering post‑quantum cryptography. The U.S. Treasury is also incorporating digital assets into broader quantum‑readiness planning.

Outlook

The August 26 transaction proves that a migration tool exists for funds whose public keys are still hidden, but a protocol‑level solution is still needed to protect the millions of BTC that are already exposed.