Crypto support

[arlyon]

Hi!

I have been messing around w/ the esp and would like to add a hal impl for the hardware hmac signing / DS on the esp32 c3 (and more). I assume that would happen in esp-idf-svc, but I'm opening this issue to make sure I'm targeting the right place.

As a side note, really enjoying working w/ this ecosystem! :tada:

[ivmarkov]

I think you should rather do this in esp-idf-hal, as the hardware HMAC / DS is a "device" (and as a matter of fact, EspWifi and EspEth* should also be moved to esp-idf-hal as they also rely on hardware devices (the modem in the case of EspWifi and the SPI/EMAC controllers in the case of EspEth, but it is a gray area for those as they are mixing the ethernet layer with the IP layer in a single trait)).

Also, esp-idf-hal/esp-idf-svc is all about wrapping ESP-IDF drivers & APIs, so you probably need to wrap this and this API in your impl. If you are looking to implement a bare-metal driver, it probably belongs to the esp-hal crate, not to esp-idf-hal.

What I would suggest is to first of all make sure that the above ESP-IDF APIs are exposed by esp-idf-sys. If they are not, you need to contribute a PR to esp-idf-sys which includes the relevant ESP-IDF headers here.

Once you have the unsafe bindings to the HMAC/DS ESP-IDF APIs in esp-idf-sys, you can write your own code that calls these APIs to e.g. sign with the HMAC key. If this works, the next step indeed is to indeed write a typesafe "driver" in esp-idf-hal that actually wraps the unsafe ESP-IDF driver exposed in esp-idf-sys in the previous step.

PRs greatly appreciated!

[arlyon]

I appreciate your direction. Will see if I can woth a solution together for simple upstream hmac, though I don't have an ETA until I explore further.

Cheers

[olanod]

Perhaps worth mentioning that it would be nice for a crypto module to implement the embedded friendly traits of RustCrypto