DF8: Is the nonce byte necessary?

ruuvi / ruuvi-sensor-protocols

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Closed ojousima closed 5 years ago

ojousima commented 5 years ago

The nonce byte was discussed on Slack, in short:

The ECB mode has a weakness when large blocks of data are encrypted: Large data is split to 16-byte chunks and identical plaintext leads to identical cipher text.
- This weakness does not apply to Ruuvi data, as there is a running counter, sensor noise and data is less than 16 bytes.
- Therefore, nonce is not required and it can be deleted.

If anyone has counterarguments, please let us know

ojousima commented 5 years ago

If the nonce is removed, the CRC can be moved to the place of nonce. This frees up one more byte for encrypted payload.

ojousima commented 5 years ago

Fixed in 0f85fec