ИМХО, самый простой способ.
Можно кучу вариаций на эту тему
SQL>
SQL> select
2 "туда"
3 ,utl_raw.cast_to_varchar2(utl_raw.bit_xor(utl_raw.cast_to_raw("туда")
4 ,utl_raw.cast_to_raw('SecretPattern'))) "обратно"
5 from (
6 select
7 utl_raw.cast_to_varchar2(utl_raw.bit_xor(utl_raw.cast_to_raw('hello')
8 ,utl_raw.cast_to_raw('SecretPattern'))) "туда"
9 from dual)
10 ;
туда обратно
-------------------------------------------------------------------------------- --------------------------------------------------------------------------------
; hello