Bresser Water Leakage sensor checksum algorithm

I am trying to decode the Bresser Water Leakage sensor, the current state of work can be found in https://github.com/matthias-bs/rtl_433/blob/master/src/devices/bresser_leakage.c

I have also created an issue with some background information for integrating the decoder in the rtl_433 project.

Decoding the payload works fine, but I did not find out how the checksum is calculated. The data layout and samples are provided in bresser_leakage.c.

I have already tried the following:

1. Digest calculations used in rtl_433 decoders for other Bresser sensors

• with varying payload lengths)
• with iterating the key in the range 0...0xFFFF

4. revdgst (with varying payload lengths)

5. reveng (with varying payload lengths) - no meaningful result at all

6. CRC calculators on https://crccalc.com/

7. Simple checksum algorithms like ADD, XOR, SUB

• on bytes
• on nibbles
• on 16-bit chunks

8. Parity

• bits set - byte wise/nibble wise, first/second half of message, ...

None of these attempts were successful.

I would be happy if anyone could help.

Thank you very much in advance!

Matthias