OTA Firmware Upload does not work with Encryption

[jamesmunns]

Currently, the Bootloader does not appear to support Encryption (specifically AES-128 with the NRG family).

This causes a problem when the user is using encryption in the User Application, but would like to use SwapDMT-cmd for OTA firmware update.

The software will need to be updated with one of the following fixes:

1. The SwapDMT application should switch to unencrypted mode when uploading firmware
   • This might be the easiest approach, should be fixable only in the Python tools
   • However then the firmware will be transmitted unencrypted
2. Add encryption support in the Bootloader, and store the AES key somewhere accessible from both, such as an nvram buffer
   • This would not be backwards compatible with previous versions of the bootloader
   • This would be more secure

We have developed a workaround right now by merging the encryption code from the Application's SWAP into the bootloader and recompiling, but it does not seem to be general enough to share here.

I am filing this issue here, because it may affect a few different repos (SWAP lib, Python Tools, etc).