He won't go https, sign his binaries, or enable mark-of-web either. It's strange to see people still playing small binary golf in 2018.
It seems to use 7-Zip and/or p7zip binaries.
I'm not sure what other FOSS alternative to use. BandiZip is free (as in beer) but doesn't seem to have an update since Sept, so if it uses p7zip under the hood for 7z, it's also vulnerable.