This is a book about a change that has already been scheduled.
Somewhere in the next decade, the mathematics that proves you own your coins is going to be replaced. Not patched — replaced. The signatures your wallet makes today belong to a family of problems that a large enough quantum computer can solve backwards, working from a public key to the private key it was supposed to protect. No such computer exists yet. That sentence is true as this book is written, in November 2026, and this book will keep returning to it, because everything honest about this subject hangs on knowing exactly which parts are settled and which parts are still guesses.
Here is what is settled.
The replacement signatures exist. In August 2024, after an eight-year public competition, the United States National Institute of Standards and Technology published the finished standards: ML-DSA and SLH-DSA for signatures, built to survive the machine that breaks the old ones. The deadlines exist too. The same institute has set the dates after which the old algorithms are deprecated (2030) and then disallowed (2035) in the systems it governs, and governments and standards bodies on several continents have published timelines in the same window. And the cost of the change is known, because it can be measured in bytes: a signature that takes about 64 bytes today will take roughly 2,400 to 4,600 bytes in its standard replacement, and nearly 50,000 in the most conservative one. The future, in this case, is not mysterious. It is merely large.
Here is what is not settled. Nobody knows when a quantum computer capable of breaking today's signatures will be built. The honest estimates from the people building them range across years to decades, and this book will show you those estimates with their sources rather than pick one and pretend. Nobody has chosen the post-quantum signature scheme for Bitcoin; there are drafts, and drafts are all they are. And nobody — no foundation, no wallet maker, no standards body — has yet written the instructions you will one day follow to move your coins, because the address type you will move them to does not exist yet.
A book that hid those gaps would be selling you something. This one takes the other road, and it is worth saying plainly what that road gives you:
For everything you need to do now, this book contains complete solutions. The practices that keep a holder safe in the meantime — how addresses expose their keys and when, how to keep a seed the way it deserves to be kept, how to sign without your keys ever touching the internet, how to change devices without changing wallets, and how to change wallets when a device is in doubt — are finished, documented, and testable today. Nothing in that half of the book depends on a roadmap.
For the change itself, this book contains the complete map as it stands: the standards, the deadlines, the exposure — how much coin sits where a future machine could reach it, counted several ways by several counters — and the state of each major chain, including one that has already made the crossing and can be visited today. Where the map runs out, it says so, in a chapter of unknowns that is part of the book and not an apology appended to it.
You will not find quantum physics here beyond the one idea the whole thing turns on: a signature is a proof made from a secret, and a new kind of computer threatens the hiding of that secret. This is not a book about the machine. It is a book about a transition — written for the people who will have to make it, holding what they hold, with the tools that exist today.
It is dated, deliberately. November 2026. When the facts move, the facts that were true on that date will still be the record of what a careful holder knew, and when.
— The Author
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