Glassnode: 20% of Bitcoin Exposed to Potential Quantum Attacks

Glassnode analysts found roughly 20% of Bitcoin’s circulating supply is held in outputs where public keys are already visible on-chain or where address reuse makes keys effectively exposed. The finding comes from a recent analysis of the UTXO set and transaction history.

The firm identified coins tied to legacy output types and repeated-address patterns. When a transaction spends from legacy pay-to-public-key (P2PK) outputs, or when spending from pay-to-public-key-hash (P2PKH) addresses that have been reused or consolidated, the public key appears on the blockchain. Those visible public keys were the focus of the analysis.

Glassnode highlighted a specific threat model in which an adversary records public keys now and attempts to recover the corresponding private keys later if sufficiently powerful quantum hardware becomes available. Algorithms such as Shor’s algorithm can, in principle, derive private keys from public keys for elliptic curve cryptography, a capability that would enable such “harvest now, decrypt later” attacks.

The report clarified that the exposure results from how keys and addresses have been handled over time rather than from a defect in Bitcoin’s protocol or wallet software. The firm did not identify bugs in Bitcoin Core or other wallet implementations as causes. Glassnode wrote: “This exposure is driven by on-chain behavior — public key revelations and address reuse — and not by a weakness in Bitcoin’s protocol or implementation.”

Modern address formats and signature schemes reduce the amount of key material visible on-chain until spending. Pay-to-script-hash (P2SH) and SegWit variants show less key data before spend, and Taproot with Schnorr signatures alters how keys and scripts appear. To date, no quantum computer has demonstrated the ability to break secp256k1, the elliptic curve used by Bitcoin.

The report noted options available to developers, custodians and wallet providers to limit future exposure. These measures include avoiding address reuse, sweeping funds to new keys before public-key disclosure, and researching post-quantum signature schemes. Glassnode’s analysis does not set a timeline for any required changes and presents the issue as a matter of historical key exposure and custodial practice rather than an immediate software failure.