System.Security.Cryptography.CryptographicException: Key not valid for use in specified state

今日測試時，在下列第二行一直發生System.Security.Cryptography.CryptographicException: Key not valid for use in specified state 的錯誤。中文訊息是「機碼用在特定狀態時無效」

RSACryptoServiceProvider provider = cert.PrivateKey as RSACryptoServiceProvider;

RSAParameters signPrivateKey = provider.ExportParameters(true);

沒看過耶！查了 Google 大神也是無效。
結果，重匯 pfx (即有私鑰的憑證) 就好了？

真是怪

今日證實，是程式寫錯了。
使用provider.ExportParameters(true)，即將私鑰匯出，這是不對的。
我只需要將私鑰拿來簽章即可。
如下

      XmlDocument doc = new XmlDocument();
      doc.LoadXml(origXml);

      //匯入私鑰
      X509Store store = new X509Store(StoreName.My, StoreLocation.LocalMachine);
      store.Open(OpenFlags.ReadOnly);
      X509Certificate2Collection certs = store.Certificates.Find(X509FindType.FindByThumbprint, certificateThumbPrint, true);
      if (certs.Count == 0)
        throw new CryptographicException("The certificate could not be found.");

      X509Certificate2 cert = certs[0];

      RSACryptoServiceProvider provider = cert.PrivateKey as RSACryptoServiceProvider;

      SignedXml signXml = new SignedXml(doc);
      signXml.SigningKey = provider;