Comment by vbezhenar
2 years ago
I thought about this technology for bitcoin offline wallet. So like you'll get any mobile phone, install some bitcoin app, put it to aircraft mode (or even destroy all wireless chips if you can do that). Or just laptop. Then you'd use it to generate wallet, sign transaction and then QR this transaction and receive it via another phone which is connected to the internet. So private key is never leaving offline device and all communication with the outside world is through human-eye controllable channel. Should be impossible to compromise using digital methods (assuming that wallet application is trustworthy).
SeedSigner does this, using an RPi with screen/camera.
https://seedsigner.com
Coldcard does this with a microSD card which seems more secure than broadcasting light. Using open source wallet like Sparrow and running own Bitcoin node with Electrum server further improves security and privacy.
That’s what we did when we built air-gapped Bitcoin cold storage: https://github.com/square/subzero