do you have your source with the keys you used? if yes then you can unpack
if not search on google , few years ago there was a tool that could show you the keys of a client , i dont know if it still functional of even somewhere.
giving the fact that you have access to binary source you can use this:
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just open xtea_keys_generator.py and where genKey() put your your keys from static DWORD s_adwEterPackKey[] and static DWORD s_adwEterPackSecurityKey[] .
it should generate your hex in order to unpack
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