Here is a Medium post which describes how the protection works:
https://medium.com/@th4jouke/reversing-and-decrypting-a-case-of-kixtart-7ecc4350dd6a

Here is the C code for the detokenizer written by the author of the Medium post:
https://gist.githubusercontent.com/dvice...x-Decryptgist.c

Here is a different detokenizer which is written in Python:
https://github.com/jhumble/Kixtart-Detokenizer