One of the challenges of the GreHack2019 CTF was a white-box. The White-box has been pushed to the SideChannelMarvels Project.
White-box cryptography is presented here : http://www.whiteboxcrypto.com/. If you are not fammilair with the concept, Brecht Wyseur itroduced it well in "white-box cryptography: hiding keys in software", MISC magazine, April 2012
The GreHack2019 CTF white-box is very classic AES128 white-box implementation. The fact that it implements an AES can be found by having a look to the code and by identifying the 11 rounds or by simply looking to the input sample "Who Is Rijndael".