Bitcoin exchanges can reduce quantum exposure before a network upgrade

A forthcoming quantum‑safe version of Bitcoin will require changes across the entire ecosystem that holds and moves today’s coins. Exchanges, custodians, hardware wallets and key‑management platforms must adopt new rules while still processing deposits, withdrawals and recoveries.

Operational challenge highlighted by Coinbase workshop

Coinbase hosted a closed‑door workshop on September 9 with Stanford and Localhost Research, bringing together developers, cryptographers, custodians and hardware‑wallet experts. Participants did not reach consensus on a specific post‑quantum approach and identified trade‑offs involving transaction size, hardware performance, key management and adoption.

Scale of current exposure

Glassnode’s May data showed roughly 1.6 million BTC in exchange‑related outputs with public keys visible on‑chain, representing about 40 % of the operationally exposed total identified in the study. The firm estimated that 6.04 million BTC (30.2 % of the issued supply) had public‑key exposure at rest, with 1.92 million BTC classified as structurally exposed and 4.12 million BTC exposed due to operational behavior such as address reuse.

Long‑exposure vs short‑exposure attacks

Public‑key visibility creates two risk windows:

• Long‑exposure attacks target keys that remain visible on‑chain for extended periods.
• Short‑exposure attacks target keys revealed only after a transaction enters the mempool, giving an attacker a brief window before confirmation.

Exchanges hold the largest share of the operational exposure bucket, making them a critical test case for mitigation.

Potential mitigation pathways

Two parallel tracks are emerging:

1. Address hygiene and output redesign: Improving address reuse practices and moving balances to safer output types, such as the proposed Pay‑to‑Merkle‑Root (P2MR) defined in BIP‑360, can reduce long‑exposure risk.
2. Post‑quantum signature adoption: Research into hash‑based, lattice‑based and isogeny‑based signatures is ongoing. Benchmarks from Blockstream Research show hardware wallets can generate hash‑based post‑quantum signatures, while BitGo and Silence Laboratories simulated multi‑party computation wallets using ML‑DSA.

Next steps for custodians and developers

Exchanges can start by mapping exposed balances, reducing address reuse, and testing new key‑generation and backup procedures. Developers should continue evaluating P2MR alongside candidate post‑quantum signature schemes to address both long‑ and short‑exposure windows.

The roughly 1.6 million BTC identified by Glassnode provides a concrete cohort for testing large‑scale migration, but dormant coins and broader ecosystem consensus remain unresolved challenges.