New Review Finds at Least 4.83 Million Bitcoin (BTC) Exposed to Quantum Risk

At block 959,193 on Sept. 13, 2026, unspent outputs with visible public keys totaled at least 4,831,444 BTC. It put that total at about 24.1% of unspent Bitcoin at block 959,193, framing it as a minimum measure of potential exposure.

The reconstruction classified 1,715,969 BTC as structurally exposed and at least 3,115,944 BTC as operationally exposed, with 469 BTC counted in both categories. Its operational tally excludes cases its method could not confirm, so the total is a floor.

A May 20, 2026 estimate put Bitcoin exposed at rest at 6.04 million BTC, or 30.2% of issued supply, including 1.92 million structurally exposed BTC and 4.12 million operationally exposed BTC.

The two totals are not directly comparable: one uses issued supply as its denominator, while the other measures unspent Bitcoin at a specified block. Their methods also classify exposure differently. Exposure at rest means a public key is already visible; it does not mean the associated coins can be taken with current machines.

Bitcoin uses elliptic-curve signatures to authorize transactions. In theory, a sufficiently capable, error-corrected quantum computer running Shor’s algorithm could use an exposed public key to derive the private key needed to spend the associated coins. Current quantum computers cannot carry out that attack.

Under specified hardware and error-correction assumptions, a modeled attack on the relevant elliptic-curve problem required fewer than 500,000 physical qubits and 18 to 23 minutes. The estimate concerns computing resources; it does not predict when such a machine might exist.

The National Institute of Standards and Technology (NIST) finalized FIPS 203, 204 and 205 on Aug. 13, 2024. FIPS 204 and 205 specify digital-signature standards, while FIPS 203 covers key encapsulation. Moving a blockchain to new cryptography would involve changes to network software, wallets and custody systems, with dormant or inaccessible holdings posing a migration challenge.

The nine-member Quantum Alliance plans to develop shared readiness criteria and work on migration, wallet security, post-quantum zero-knowledge systems and cross-chain compatibility. It also plans public tests and benchmarks for signatures, key management, consensus, zero-knowledge proofs and peer-to-peer connections.