Oracle PL/SQL for DBAs

MD5 Hashing in Oracle9i Database

Let’s see how we can use hashing in real-life database administration. When a sensitive piece of information is sent to a different location, you might calculate the hash value beforehand and send it in another shipment or transmission. The recipient can then calculate the hash value of the received data and compare it against the hash value that you sent out.

In Oracle9i Database, the DBMS_OBFUSCATION_TOOLKIT package provides a hashing function for MD5, an implementation of the Message Digest protocol. To hash a string, I might specify:

    DECLARE
       l_hash     VARCHAR2 (2000);
       l_in_val   VARCHAR2 (2000);
    BEGIN
       l_in_val := 'Account Balance is 12345.67';
       l_hash := DBMS_OBFUSCATION_TOOLKIT.md5 (input_string => l_in_val);
       l_hash := RAWTOHEX (UTL_RAW.cast_to_raw (l_hash));
       DBMS_OUTPUT.put_line ('Hashed Value = ' || l_hash);
    END;
    /

Here I provided a simple string “Account Balance is 12345.67”, and got its hash value. The MD5 function returns a VARCHAR2 value, but as in the encryption process observed earlier, it contains control characters. Hence, I must convert it to RAW and then to hexadecimal for easy storage. The above code segment returns:

    Hashed Value = A09308E539C35C97CD612E918BA58B4C

In this example, you will note two important differences between hashing and encryption:

• In hashing, the input string does not have to be padded to make it a certain length, whereas it does in encryption.

• In hashing, there is no key. Because there is no key involved, there is no ...