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...