public class UserAuthentication
 {
     //authentication kontrolleri
     public bool CheckUser(string userName, string password)
     {
         var enryptedPassword = EncrypData(password);

         var user = IsExistUser(userName, enryptedPassword);

         return user != null;

     }

     //database işlemleri
     private User IsExistUser(string userName, string password)
     {
         var reader = new SqlCommand("query", new SqlConnection("connection string")).ExecuteReader();

         return reader.HasRows ? MapUser(reader) : null;
     }

     //mapping işlemleri
     private User MapUser(SqlDataReader reader)
     {
         return new User()
                    {
                        Id = reader["Id"].ToString(),
                        UserName = reader["UserName"].ToString(),
                        Password = reader["Password"].ToString()
                    };
     }

     //şifreleme işlemleri
     private string EncrypData(string password)
     {
         var provider = new System.Security.Cryptography.RSACryptoServiceProvider();

         provider.ImportParameters(new RSAParameters(){D = new byte[]{3,4,6,7}});

         return provider.Encrypt(System.Text.Encoding.UTF8.GetBytes(password), true).ToString();
     }
 }