Oracle data masking

Question

We have one requirement to mask a particular table column using a Oracle function which gives persistent masked output string.

• We tried Oracle Hash Function but it does not give String type return value.
• We tried Oracle Random function (dbms_random.string) but it does not give Persistent output string.

I read on internet that this is called deterministic masking. But we do not want to use Oracle Enterprise Manager; however we require a direct Oracle function.

Please suggest.

Answer 1

This problem is easily solved in 12c with the function STANDARD_HASH.

The solution in previous versions is only slightly more complicated. Build a simple wrapper around DBMS_CRYPTO that acts just like STANDARD_HASH:

--Imitation of the 12c function with the same name.
--Remember to drop this function when you upgrade!
create or replace function standard_hash(
    p_string varchar2,
    p_method varchar2 default 'SHA1'
) return varchar2 is
    v_method number;
    v_invalid_identifier exception;
    pragma exception_init(v_invalid_identifier, -904);
begin
    --Intentionally case-sensitive, just like the 12c version.
    if p_method = 'SHA1' then
        v_method := dbms_crypto.hash_sh1;
    --These algorithms are only available in 12c and above.
    $IF NOT DBMS_DB_VERSION.VER_LE_11 $THEN
        elsif p_method = 'SHA256' then
            v_method := dbms_crypto.hash_sh256;
        elsif p_method = 'SHA384' then
            v_method := dbms_crypto.hash_sh384;
        elsif p_method = 'SHA512' then
            v_method := dbms_crypto.hash_sh512;
    $END
    elsif p_method = 'MD5' then
        v_method := dbms_crypto.hash_md5;
    else
        raise v_invalid_identifier;
    end if;

    return rawToHex(dbms_crypto.hash(utl_raw.cast_to_raw(p_string), v_method));
end;
/

You may need to logon with SYS and grant your user access to DBMS_CRYPTO to make the function work:

grant execute on sys.dbms_crypto to <your_schema>;

Create a public synonym, grant it to everyone, and it works exactly the same way.

create public synonym standard_hash for <schema with function>.standard_hash;
grant execute on standard_hash to public;

select standard_hash('Some text', 'MD5') from dual;
    9DB5682A4D778CA2CB79580BDB67083F

select standard_hash('Some text', 'md5') from dual;
    ORA-00904: : invalid identifier

Here is a simple example of using the function:

update some_table
set column1 = standard_hash(column1),
    column2 = standard_hash(column2);

But updating large amounts of data can be slow. It may be faster to create a new table, drop the old one, rename the new one, etc. And the hash value may be larger than the column size, it may be necessary to alter table some_table modify column1 varchar2(40 byte);

It amazes me how many products and tools there are to do such a simple thing.