From .NET verify a dll has valid signature and has not been modified

Question

My c# .NET program accesses a c++ library.

The library is signed with a certificate and is in the same folder as the program.

At runtime, before i load the c++ library, i want to make sure the library is really mine and has not been tampered with.

I have been able to get the certificate from my dll and verify the certificate :

X509Certificate2 cert = new X509Certificate2(X509Certificate.CreateFromSignedFile(filename));
Console.WriteLine(cert.Issuer);`
cert.Verify();`

This tells me the file certificate is ok, but if I then hexedit my file and run my program again, the certificate still validates ok.

Where can I find in the certificate the hash of my library (not the hash of the certificate) and how can I create the hash of my library to compare them so I can detect the file being tampered with?

I suspect it should be simple, maybe I overlooked something.

Answer 1

PInvoke the native Windows API WinVerifyTrust , which is documented by Microsoft at MSDN with a sample in C.

There might be managed examples by others if you use a search engine.