> 1. If you hold your coins at a regulated exchange, sure yeah the authorities can probably get a warrant and seize your Bitcoins.
> 2. If you hold your coins in your own wallet but you write down your private key in, like, your phone’s notes app, and it backs up to the cloud, then the authorities can probably get your cloud provider to give them access to your notes and read the key and use that to seize all your Bitcoins. (This happened to the alleged Bitfinex hack launderers.)
> 3. If you write your private key on a scrap of paper, the authorities can search your house until they find it and seize all your Bitcoins.
> 4. If you memorize your private key, or just write it down somewhere really safe, then they can arrest you and throw you in jail until you tell them what it is, and then seize all your Bitcoins.