static void ImplicitSSLExample()
{
  try
  {
    FtpClient ftp = new FtpClient();
    //ftp.TraceWriter = Console.Out;

    // Subscribe to the CertificateReceived event
    ftp.CertificateReceived += new CertificateReceivedEventHandler( OnCertificateReceived );

    // Pick an authentication method
    AuthenticationMethod authenticationMethod = AuthenticationMethod.Ssl;

    // Pick verification flags. If unsure, pick 'None'.
    VerificationFlags verificationFlags = VerificationFlags.None;

    // Supply a client certificate to submit to the server. This example doesn't use one
    Certificate clientCertificate = null;

    // Connect implicitly to the server using encryption. Notice the port number reserved for this
    // This form always enables encryption for the data channel (for file transfers)
    ftp.Connect( "localhost", 990, authenticationMethod, verificationFlags, clientCertificate );

    try
    {
      // Login. The exchanged information will be encrypted
      ftp.Login( "username", "password" );

      /* Perform your file transfers */
    }
    finally
    {
      // Make sure we always disconnect
      ftp.Disconnect();

      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 OnCertificateReceived( object sender, CertificateReceivedEventArgs e )
{
  // The Status argument property tells you if the server certificate was accepted
  // based on the VerificationFlags provided in the call to Connect().
  if( e.Status != VerificationStatus.ValidCertificate )
  {
    Console.WriteLine( "The server certificate is invalid: {0}", e.Status.ToString() );
    Console.WriteLine( e.ServerCertificate.ToString() );

    // You have three choices here:
    //
    //  1) Refuse the certificate by setting e.Action to VerificationAction.Reject,
    //      thus making the authentication fail. This is e.Action's default value
    //      when the server certificate isn't valid.
    //
    //  2) Set e.Flags to less restrictive criterion and ask the library to
    //      validate the certificate again by setting e.Action to
    //      VerificationAction.VerifyAgain.
    //
    //  3) Force the library to accept this certificate by setting e.Action to
    //      VerificationAction.Accept.
    //
    // We'll do #1 or #3, depending on the user's answer.

    Console.WriteLine( "Do you want to accept this certificate anyway? [Y/N]" );

    int answer = Console.Read();
    if( ( answer == 'y' ) || ( answer == 'Y' ) )
    {
      e.Action = VerificationAction.Accept;
    }
  }
  else
  {
    // e.Action's default value is VerificationAction.Accept
    Console.WriteLine( "Valid certificate received from server." );
  }
}