Tshark LUA Bytes functions

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Hi,

i'm new to lua programming and am trying to create a lua script in conjonction with tshark. My goal is to get a xor key which is in the packet and apply it to the entire data field. It's a malware.

I've found many string functions but how do I get a part of my data.data. Example myvar = data.data[1 to 8 ] Type of data.data = userdata and it's a sequence of bytes https://www.wireshark.org/docs/dfref/...

Can anyone please advise ? Regards k4nfr3