how to do an update of the already encrypted data

From: <aithssaine.sanae_at_gmail.com>
Date: Mon, 13 Jul 2015 06:40:51 -0700 (PDT)
Message-ID: <70e9d6a5-f852-475b-b0ff-9ced242752c1_at_googlegroups.com>

hello
i really need help im working on transparent data encryption i use this trigger to encrypte data

create or replace trigger encrypt_emp_rand   before insert on emp
  for each row
  declare
  l_key RAW(16) := dbms_crypto.randombytes(8);   v_key varchar2(50);
  begin
  v_key := utl_raw.cast_to_raw(l_key);
:new.id:=encryption(:new.id,l_key);
:new.nom:=encryption(:new.nom,l_key);
:new.prenom:=encryption(:new.prenom,l_key);
:new.salaire:=encryption(:new.salaire,l_key);
:new.image:=l_key;
end;
  /
  show errors;
it work's when i insert data on table
i need to do this update
update emp set prenom=prenom||'XX'    

Can someone help me Received on Mon Jul 13 2015 - 15:40:51 CEST