[Cryptography] Open source encrypted file system for cheap IoT device?

[Henry Baker]

Any suggestions for a simple encrypted file system
for a $10-20 IoT device?

It doesn't have to be terribly fast, it doesn't
have to have be very sophisticated, but it does
have to have a small program memory footprint
and it does have to be reasonably secure, as it
may end up holding personal bio data.

For the moment, I'm thinking about using an uSD
card for the memory itself (uSD price not included!).

Ideally, the entire uSD card is preformatted with
random bits, so you won't even be able to tell how
much (if any) data is stored on the card.

If someone looks at this uSD card w/o the proper
key, they shouldn't be able to determine anything
except reformat the card for some other purpose.