How To Send a Client Certificate

Here is an example on how to send a client certificate when making a SSL connection.

C#
VB.NET

static void ClientCertificateExample()

{

  try

  {

    FtpClient ftp = new FtpClient();

    //ftp.TraceWriter = Console.Out;



    // Subscribe to the CertificateReceived event

    ftp.CertificateReceived += new CertificateReceivedEventHandler( OnCertificateReceived );



    // Subscribe to the CertificateRequired event

    ftp.CertificateRequired += new CertificateRequiredEventHandler( OnCertificateRequired );



    // Connect to the server normally, unencrypted, at the usual ftp port

    ftp.Connect( "localhost", 21 );



    try

    {

      // Pick an authentication method

      AuthenticationMethod authenticationMethod = AuthenticationMethod.Ssl;



      // Pick verification flags. If unsure, pick 'None'.

      VerificationFlags verificationFlags = VerificationFlags.None;



      /* In this example, we will not provide a client certificate at Connect(). Instead,

       * we subscribe to the CertificateRequired event and if the FTP server asks us for

       * a certificate, we will provide one at that time. 

       * 

       * That way, if the server is not configured to expect a certificate, it 

       * won't receive one for no reason. */



      // The client certificate to submit to the server

      Certificate clientCertificate = null;



      // Decide if the data channel (for file transfers) will be encrypted or not

      DataChannelProtection dataChannelProtection = DataChannelProtection.Private;



      // Authenticate and encrypt the connection

      ftp.Authenticate( authenticationMethod, verificationFlags, clientCertificate, dataChannelProtection );



      // Login. The exchanged information will be encrypted

      ftp.Login( "username", "password" );



      /* Perform your file transfers */

    }

    finally

    {

      // Make sure we always disconnect

      ftp.Disconnect();



      ftp.CertificateRequired -= new CertificateRequiredEventHandler( OnCertificateRequired );

      ftp.CertificateReceived -= new CertificateReceivedEventHandler( OnCertificateReceived );

    }

  }

  catch( Exception exception )

  {

    // Output some information about it

    Console.WriteLine( "-->{0}: {1}\n{2}", exception.GetType().Name, exception.Message, exception.StackTrace );



    // Fetch the inner exception

    exception = exception.InnerException;



    // While there is an exception

    while( exception != null )

    {

      // Output some information about it

      Console.WriteLine( "-->Inner exception: {0}: {1}\n{2}", exception.GetType().Name, exception.Message, exception.StackTrace );



      // Fetch the inner exception

      exception = exception.InnerException;

    }

  }

}



static void OnCertificateRequired( object sender, CertificateRequiredEventArgs e )

{

  try

  {

    /* The .NET framework exposes certificates using the X509Certificate2 class.

     * The FTP component wraps this class into the Certificate class.

     * The class can load X509 certificate files encoded in the DER or Base64 encoding.

     * Most certificate files are encrypted and require a password, often called

     * the private key, to decode them. */



    // Load a certificate file to submit to the server

    Certificate clientCertificate = new Certificate( @"D:\Xceed\MyX509Certificate.der", "certificate password" );



    e.Certificate = clientCertificate;

  }

  catch( System.Security.Cryptography.CryptographicException )

  {

    // Trigger failure by not providing a certificate

    e.Certificate = null;

  }

}



static void OnCertificateReceived( object sender, CertificateReceivedEventArgs e )

{

  // Always accept the certificate

  e.Action = VerificationAction.Accept;

}

    Private Shared Sub ClientCertificateExample()

      Try

        Dim ftp As New FtpClient()

        'ftp.TraceWriter = Console.Out;



        ' Subscribe to the CertificateReceived event

        AddHandler ftp.CertificateReceived, AddressOf OnCertificateReceived



        ' Subscribe to the CertificateRequired event

        AddHandler ftp.CertificateRequired, AddressOf OnCertificateRequired



        ' Connect to the server normally, unencrypted, at the usual ftp port

        ftp.Connect("localhost", 21)



        Try

          ' Pick an authentication method

          Dim authenticationMethod As AuthenticationMethod = AuthenticationMethod.Ssl



          ' Pick verification flags. If unsure, pick 'None'.

          Dim verificationFlags As VerificationFlags = VerificationFlags.None



'           In this example, we will not provide a client certificate at Connect(). Instead,

'           * we subscribe to the CertificateRequired event and if the FTP server asks us for

'           * a certificate, we will provide one at that time. 

'           * 

'           * That way, if the server is not configured to expect a certificate, it 

'           * won't receive one for no reason. 



          ' The client certificate to submit to the server

          Dim clientCertificate As Certificate = Nothing



          ' Decide if the data channel (for file transfers) will be encrypted or not

          Dim dataChannelProtection As DataChannelProtection = DataChannelProtection.Private



          ' Authenticate and encrypt the connection

          ftp.Authenticate(authenticationMethod, verificationFlags, clientCertificate, dataChannelProtection)



          ' Login. The exchanged information will be encrypted

          ftp.Login("username", "password")



          ' Perform your file transfers 

        Finally

          ' Make sure we always disconnect

          ftp.Disconnect()



          RemoveHandler ftp.CertificateRequired, AddressOf OnCertificateRequired

          RemoveHandler ftp.CertificateReceived, AddressOf OnCertificateReceived

        End Try

      Catch exception As Exception

        ' Output some information about it

        Console.WriteLine("-->{0}: {1}" & Constants.vbLf & "{2}", exception.GetType().Name, exception.Message, exception.StackTrace)



        ' Fetch the inner exception

        exception = exception.InnerException



        ' While there is an exception

        Do While exception IsNot Nothing

          ' Output some information about it

          Console.WriteLine("-->Inner exception: {0}: {1}" & Constants.vbLf & "{2}", exception.GetType().Name, exception.Message, exception.StackTrace)



          ' Fetch the inner exception

          exception = exception.InnerException

        Loop

      End Try

    End Sub



    Private Shared Sub OnCertificateRequired(ByVal sender As Object, ByVal e As CertificateRequiredEventArgs)

      Try

'         The.NET framework exposes certificates using the X509Certificate2 class.

'         * The FTP component wraps this class into the Certificate class.

'         * The class can load X509 certificate files encoded in the DER or Base64 encoding.

'         * Most certificate files are encrypted and require a password, often called

'         * the private key, to decode them. 



        ' Load a certificate file to submit to the server

        Dim clientCertificate As New Certificate("D:\Xceed\MyX509Certificate.der", "certificate password")



        e.Certificate = clientCertificate

      Catch e1 As System.Security.Cryptography.CryptographicException

        ' Trigger failure by not providing a certificate

        e.Certificate = Nothing

      End Try

    End Sub



    Private Shared Sub OnCertificateReceived(ByVal sender As Object, ByVal e As CertificateReceivedEventArgs)

      ' Always accept the certificate

      e.Action = VerificationAction.Accept

    End Sub