Someone breaks into your house, puts a gun to your head and demands your Bitcoin. You physically can't hand it over. That's what proper custody looks like, and it's why one of the most radical ideas in Bitcoin is that it could bring silence to systemic violence. Bitcoin won't stop crimes of passion. But no man is better than his incentives, and the uncomfortable truth is that crime does pay. You can acquire assets through stealing and extortion, and physical property is what makes that profitable. Gold in your closet can be seized by any man willing to threaten you for it. Bitcoin is the first non-physical property that can be directly owned, which makes it far harder to seize by force. Domain names came close, but a centralized third party controls them, so they can be seized by legal coercion. Bitcoin has no third party to coerce. Hold your own keys and you hold a bearer asset, like gold coins that aren't physically there. Ownership comes down to keeping a secret. That secret only protects you if you custody it properly. Write your private key (the password to your coins) on paper and lock it in a safe, and you've turned non-physical property back into physical property, seizable like the gold. Multi-key solves this. Picture the nuclear launch scene, men with briefcases handcuffed to their wrists, 2 or 3 keys turned together in sequence before anything fires. You can hold Bitcoin the same way. Break the private key into 3 pieces, or 5, or 7, called shards, and require a simple majority to move funds, 2 of 3 or 3 of 5, in a sequence you designate. Then distribute them across your circle of trust. Your accountant holds one, your lawyer another, you hold the third. Nothing moves without you, so you keep full control, and you gain redundancy, since losing one shard still leaves 2 of 3 between you and your accountant. Which brings it back to the gun. You can't hand over what you can't move. Pre-designate a safe word with your key holders, and when the thief forces you to call them, that word tells them to refuse. It's a custody schema as immune to coercion as anything you'll ever get, and it's what we trust with nuclear launch codes. In a Bitcoinized multi-key world, crime pays less. Even warfare becomes less profitable, and therefore less prevalent, thanks to Bitcoin. Bitcoin lowers the profitability of force, and humans do whatever is profitable, so the businesses built on force thin out. There are only two ways to acquire wealth. Making, where you produce and trade by consent, or taking, where you seize by force what makers have built. Bitcoin tilts the landscape of human action toward making.

Bitcoin key generation depends on entropy: the randomness behind your seed. When that randomness is weaker than expected, the seed is guessable no matter which device holds it or how long the phrase is. July's Coldcard firmware disclosure made that concrete for a lot of bitcoiners. If you generated a seed on affected firmware and later moved it to a different wallet, the weakness moved with it. Do you know where the randomness behind your seed came from?

Two of the three keys in a default Casa 3-key vault are generated by software Casa wrote: your Mobile Key and the Casa Key. We published where the entropy behind each key comes from, what each one gives up, and which ones you can replace.

How to build a Casa multi-signature vault with two hardware wallets. - Setup 2 hardware wallets from scratch (preferably, different vendors) - Build a Casa vault using 3 keys - How to receive and send Bitcoin - Optionally: How to export wallet to Sparrow Wallet

Diversify your keys, not your coins. Spread coins across multiple single sig wallets: ⬇️ chance of catastrophic loss, ⬆️ chance of partial loss. Spread 1 wallet across multiple vendor keys: ⬇️ chance of catastrophic loss, ⬇️ chance of partial loss.