If you're encrypting the data then storing it, then no. Oracle Text can only "see" the encrypted string. Not the original plaintext:
create table t (
c1 varchar2(1000),
c2 raw(1000)
);
declare
text varchar2(19) := 'red car';
text_raw raw(128) := utl_raw.cast_to_raw(text);
key raw(128) := utl_raw.cast_to_raw('thekey');
ciphertext raw(2048);
begin
ciphertext := sys.dbms_crypto.encrypt (
text_raw, dbms_crypto.des_cbc_pkcs5, key
);
insert into t values ( text, ciphertext );
end;
/
commit;
create index ti on t ( c1 ) indextype is ctxsys.context;
create index tir on t ( c2 ) indextype is ctxsys.context;
select * from t
where contains ( c1, 'red' ) > 0;
C1 C2
red car 317D79EB8F4FDC38
select * from t
where contains ( c2, 'red' ) > 0;
no rows selected