feature request: require entropy from companion app to initialize the device

[georgantas]

This post outlines how the Jade generates its entropy:

User input
- CPU counters
- Battery state
- Ambient temperature
- Multiple images taken with camera during boot
- Built-in cryptographic-strength hardware number generator
- Entropy from the Blockstream companion app

The built-in hardware cryptographic random number generator (CRNG) derives entropy from various sources, one of which is the included radio (used for Bluetooth). If you [disable radio](https://help.blockstream.com/blockstream-jade/add-more-security-functionality/disable-bluetooth) with the optional “No-Radio” firmware, the CRNG loses that source and, therefore, has reduced entropy. To mitigate this, we use an ESP32 API call named “bootloader_random_enable()” to sample raw radio noise only during boot, which is then added to the entropy pool along with the sources mentioned above.

However, Entropy from the Blockstream companion app is optional. It would be nice to require that add_entropy be called at least once with at least 32 bytes before the entropy state is considered valid:

{
    "id": "925",
    "method": "add_entropy"
    "params": {
        "entropy": <bytes>
    }
}

[jgriffiths]

Hi @georgantas thanks for the suggestion.

Given the recent coldcard incident, we are looking at ways to allow users to add more external entropy to decrease paranoia regarding wallet generated seeds. In this case we'd either need to expose an entropy QR type for QR mode, or ask users to add entropy from dice/cards etc to enforce additional entropy for qr mode.

I'll pass this suggestion through to our product team to be iterated on with other upcoming entropy changes, thanks.