Installing a certificate in a .MSI Custom Action doesn't work properly

Question

I'm trying to install a certificate in the Local Machine Store in a custom action. The certificate is installed, but when I use it to query AWS, I get this error:

Object contains only the public half of a key pair. A private key must also be provided.

The installer is running elevated, the target is Windows Vista.

If I use a separate .exe to install the exact same certificate, using the exact same code, it works. So what is it that differs when installing a certificate using the Windows Installer?

The code:

private void InstallCertificate(string certificatePath, string certificatePassword)
{
  if (IsAdmin())
  {
    try
    {
      X509Certificate2 cert = new X509Certificate2(certificatePath, certificatePassword,
        X509KeyStorageFlags.MachineKeySet | X509KeyStorageFlags.PersistKeySet);

      X509Store store = new X509Store(StoreName.My, StoreLocation.LocalMachine);
      store.Open(OpenFlags.ReadWrite);
      store.Add(cert);
      store.Close();
    }
    catch (Exception ex)
    {
      throw new DataException("Certificate appeared to load successfully but also seems to be null.", ex);
    }
  }
  else
  {
    throw new Exception("Not enough priviliges to install certificate");
  }
}

Answer 1

Well, at least this question earned me a tumble weed badge...

It turned out to be the permissions on the installed key file. I had to grant all users read permissions.

And here is the code I used to grant all (local) users read permissions:

private static void AddAccessToCertificate(X509Certificate2 cert)
{
  RSACryptoServiceProvider rsa = cert.PrivateKey as RSACryptoServiceProvider;
  if (rsa == null) return;

  string keyfilepath = FindKeyLocation(rsa.CspKeyContainerInfo.UniqueKeyContainerName);

  FileInfo file = new FileInfo(System.IO.Path.Combine(keyfilepath, rsa.CspKeyContainerInfo.UniqueKeyContainerName));

  FileSecurity fs = file.GetAccessControl();

  SecurityIdentifier sid = new SecurityIdentifier(WellKnownSidType.BuiltinUsersSid, null);
  fs.AddAccessRule(new FileSystemAccessRule(sid, FileSystemRights.Read, AccessControlType.Allow));
  file.SetAccessControl(fs);
}

private static string FindKeyLocation(string keyFileName)
{
  string pathCommAppData = System.IO.Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.CommonApplicationData), @"Microsoft\Crypto\RSA\MachineKeys");
  string[] textArray = Directory.GetFiles(pathCommAppData, keyFileName);
  if (textArray.Length > 0) return pathCommAppData;

  string pathAppData = System.IO.Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData), @"Microsoft\Crypto\RSA\");
  textArray = Directory.GetDirectories(pathAppData);
  if (textArray.Length > 0)
  {
    foreach (string str in textArray)
    {
      textArray = Directory.GetFiles(str, keyFileName);
      if (textArray.Length != 0) return str;
    }
  }
  return "Private key exists but is not accessible";
}