Previously, the test vectors were encoded into the python test scripts,
converted to base64, and send over to the device under test via stdio.
The application sent back the output after converting it to base64
first, which was read back in by the test script and decoded. Finally,
the test script compared the result with the expected result.
This made the test complex, slow and, flanky, as stdio on interfaces
such as UART has a high bit error rate and some quirks (e.g. the EDBG
UART bridge e.g. in the samr21-xpro dropping bytes when bursts of more
than 64 bytes at a time are send).
This basically rewrites the test to embed the test vectors in the
firmware and do the comparison on the devices. This fixes test failures
on the samr21-xpro, the nRF52840-DK and likely many others. Also, it
is now fast.
This add an implementation of PBKDF2 using sha256 hmac. Only one derived
key length is supported (32) though it should not be hard to extend it.
The testing is done with both random (with fixed seed) vectors amd vectors
from rfc7914.
