Support for embeded devices / hardware wallets

Here is an example of a class of devices that I would hope we could build subtx for as a target: https://ledger.readthedocs.io/en/latest/bolos/application_environment.html

• Hardware wallets that connect via USB/Bluetooth/NFC
• Air-gapped dedicated devices that would communicate via QR codes or SneakerNet

This likely would need these features:

• Support for completely offline operations
  • Including helper functions to export things like public keys, transaction data, and wait for user input before executing any kind of signing.
• no_std being used to support embedded devices (https://rust-embedded.github.io/book/intro/no-std.html)
• An interface to communicate with a generic secure enclave/element that stores keys.
• An interface to pass information via USB/Bluetooth/NFC or onboard displays (in the case of hardware wallets or air-gapped devices)

Is there such a thing avalible now? Presently the closest thing at parity I can find is https://github.com/paritytech/parity-signer , but this is not in rust, nor would it be suitable for embedded device use.

Start with the Ledger BOLOS application-environment documentation and compare parity-signer’s capabilities with subxt’s current interfaces. Scope whether offline operations, no_std, secure-element access, and USB/Bluetooth/NFC or QR/display transport can be supported; a concrete design and implementation boundary would be needed before coding.