Hoping someone might be able to correct me, I was looking at a SATSCARD and noticed this in the FAQ
At the factory, we use the Bitcoin block hash of a recent block as the chain code; this is also unpredictable since it's a product of the Bitcoin mining process.
It seems like that would enable the manufacturer to just recreate private keys because even though block hashes are random they're also public?
This got me thinking about using something you can find as a brainwallet, how hard would it be to write a script that could check if each blockhash has public addresses derived from it?