[namibj]

I was thinking about a chip with only sram for secret storage that could be bundled into a ID-1 sized card with some small energy storage for the sram (there are affordable .5mm LiPo Cells that fit inside such a card), and then use the card to fit some display capable of giving some little data out, as well as a touch matrix,possibly by just using a style similar to carbon-contacts on cheap rubber membrane keyboards, but gold plated like the smartcard interface. But it seems like you can't afford to store one decompressed ed25519 or dare rsa, so the idea is moot by virtue of requiring sub-100nm technology to fit at least some sram.