SessionOptions sessionOptions = new SessionOptions();
sessionOptions.Protocol = Protocol.Sftp;
sessionOptions.HostName = "xxx.xxx.xxx.xxx";
sessionOptions.PortNumber = 22;
sessionOptions.UserName = "user";
sessionOptions.SshPrivateKeyPath = path
 
using (Session session = new Session())
{
   try
   {
       session.Open(sessionOptions);
   }
   catch (Exception ex)
   {
       MessageBox.Show(ex.Message);
   }
}