Write-up by @doegox and @PapaZours of Quarklabs.
Many thanks to you for the job and GG for solving the first 5 levels !

Level4: [http://wiki.yobi.be/wiki/GreHack_2018_Writeups#Secret_Keeper_level_4_.28300_points.29](http://wiki.yobi.be/wiki/GreHack_2018_Writeups#Secret_Keeper_level_4_.28300_points.29)