Decrypt function

[stefan-nu]

I watched your decrypt function in grottdata.py.

This is some magic code to me. I tried to understand it. But I did not figure it out completely.
I assume the plain text gets encrypted with the key "Growatt".

I am really wondering how you came up with it.

Could you explain this part:
[decdata[i+8] ^ int(hex_mask[j],16)]

For reference the complete code

 def decrypt(decdata) :
    ndecdata = len(decdata)
    len_decdata = len(decdata) 
 
    # Create mask and convert to hexadecimal
    mask = "Growatt"
    hex_mask = ['{:02x}'.format(ord(x)) for x in mask]
    nmask = len(hex_mask)

   #start decrypt routine
    unscrambled = list(decdata[0:8])                                            #take unscramble header

    for i,j in zip(range(0,ndecdata-8),cycle(range(0, nmask))):
        unscrambled = unscrambled + [decdata[i+8] ^ int(hex_mask[j],16)]

[johanmeijer]

I read it somewhere on the internet.

[stefan-nu]

OK I understand.

As the code was not self-explanatory to me, I analysed it and figured out what it actually does.
I have updated the code to be easier to understand without changing its functionality.
https://github.com/stefan-nu/grott/commit/4c842faebd9107d0616f644e48a9f6905bd699ca

My commit also includes unit tests for the decrypt function to avoid a regression.

I could not check the performance as I have no profiler running. I am sure however that my code equally the original code is very inefficient. It would be much better to use an optimized library with encryption functions. I did not investigate into that, as I don't know if you want to use a library.