Bitcoin and the Quantum Computer: Which Addresses Already Expose Their Keys

If you hold your own Bitcoin, the most important question in the quantum debate is not a question about the future. It is one you can answer today on a block explorer: has your address ever revealed its public key? That single fact decides whether a future quantum computer could attack your coins at all. Addresses that have never sent anything do not show their key. Addresses you have spent from show it permanently. The occasion for this article is a paper that, at first glance, has nothing to do with cryptocurrencies. On September 3, 2026, the G7 Cybersecurity Working Group, chaired by France, published the joint statement "Preparing for the Post-Quantum Era: A Call to Action". The message: do not wait for the first capable quantum machine, but take stock of your own encryption now and start migrating. For you as a holder of Bitcoin, that is not an abstract matter for government agencies. The first European milestone for the switch expires at the end of this year, and the question of which of your addresses are exposed is a question of custody. This article answers three things: what on a blockchain would actually be vulnerable, how you can check your own position in a few minutes, and which deadlines the regulators have set. No price forecast, no doomsday. What the G7 statement of September 3, 2026 calls for The G7 nations are urging public authorities and companies to begin the migration to post-quantum cryptography immediately. Post-quantum cryptography is the umbrella term for encryption and signature schemes that remain secure even once a sufficiently large quantum computer exists. The paper names five fields of action: raising awareness of quantum-related risks, developing national strategies, advancing research and practical adoption, strengthening cooperation between government and industry, and anchoring post-quantum methods in security requirements and procurement. Not one of those points is addressed to retail investors. The direction they point in still concerns you: once banks, exchanges and wallet providers have to rebuild their signature schemes, the way your coins are secured will change over the medium term. What the statement explicitly does not say has a section of its own further down. That honesty belongs here, because several articles in recent days have read the paper as a warning aimed at the crypto industry. Harvest now, decrypt later: why migration starts before the quantum computer The technical term that explains the urgency appears verbatim in the G7 statement. Harvest now, decrypt later describes an attack in which data is captured and stored in encrypted form today, to be decrypted later with a quantum computer.