http://bugs.winehq.org/show_bug.cgi?id=26835
--- Comment #147 from Maarten Lankhorst m.b.lankhorst@gmail.com 2011-05-20 05:05:16 CDT --- Portal 2 appears to generate client.dll and server.dll correctly. They have a valid signature on wine just as on windows. To verify just get windows platform sdk and run this: "signtool verify /pa client.dll server.dll". Make sure you use windows, as wine allows invalid exes to pass validation.
With that I get that my client.dll and server.dll have valid signatures, so the problem appears to be a check at runtime, not the generation.