I googled around a bit and found https://github.com/OpenRA/OpenRA/blob/629fe95ebdfd669d04af5cdbdb900bf09e08e39e/OpenRA.FileFormats/Filesystem/InstallShieldPackage.cs . Reading that was enough to extract the files, though I figured out the modification date/time was in old DOS format, and that's documented at https://msdn.microsoft.com/en-us/library/windows/desktop/ms724247%28v=vs.85%29.aspx .