how to login in user with encrypted username and password

i have created a form to login my user in my application,its work fine for simple set up,but i have to access to multiple user that is way i am using a form to create a form to make a user name and password for the employee. i am using following code to encrypt user name and password.

 string passwordForEncryption = "sA23(^A1&*%1)01Ax)@!21!@#$%^&*()7984651";
 string encryptedpassword = StringCipher.Encrypt(ddlRollNo.Text, passwordForEncryption);
 string encryptedUserName = StringCipher.Encrypt(txtPassword.Text, passwordForEncryption);
 CTP.HRMS.Business.UserLogin ulogin = new Business.UserLogin();
 ulogin.Role_Id = SafeConvert.ToByte(ddlRole.SelectedValue);
 ulogin.Employee_Id = encryptedUserName;
 ulogin.Password = encryptedpassword;

and when user login i am using following code

                string passwordForEncryption = "sA23(^A1&*%1)01Ax)@!21!@#$%^&*()7984651"; 
              string encryptedpassword = StringCipher.Encrypt(txtPWD.Text, passwordForEncryption);
 string encryptedUserName = StringCipher.Encrypt(txtUserName.Text, passwordForEncryption); 
              Entities entities = new Entities(); 
            CTP.HRMS.WebApp.EF.UserLogin login = entities.UserLogins.FirstOrDefault(x =>x.Employee_Id==encryptedUserName && x.Password == encryptedpassword);
 //var login = (from u in entities.UserLogins   
          //              join ee in entities.Employees on u.Id equals ee.Id   
           //              where u.Password == encryptedpassword       
      //                    && u.UserName == encryptedUserName         
    //              select new           
  //              {           
  //                  FormalName = u.FormalName,  
           //                  gisuyag = ee.Address  
           //              }).FirstOrDefault();   
           if (login != null)         
    {                 MyUser.UserName = txtUserName.Text;    
             MyUser.Role_Id = login.Role_Id;           
    //  MyUser.FormalName = login.FormalName;
 //Create A fuield that contains full Name of logged in user for diaplay purpose    
             FormsAuthentication.RedirectFromLoginPage(login.Id.ToString(), true);  
           }               else           
  {                 
  //if data reader doesn’t contains any row, it means user name or password is           
       //incorrect                  txtUserName.Text = "";               
    txtPWD.Text = "";                
   Label3.Text = "User Name/Password not correct";          
   }         } 

how i can i do this