Verifying your data hasn't been tampered

I was recently asked how one can verify that some data in a table hasn't been changed.
A solution that comes to mind is to use the hash procedure of DBMS_CRYPTO package.
Here's a quick example of how the procedure works:

SQL> select dbms_crypto.hash(utl_raw.cast_to_raw('Some Data..'),3) from dual;

DBMS_CRYPTO.HASH(UTL_RAW.CAST_TO_RAW('SOMEDATA..'),3)
--------------------------------------------------------------------------------
7C0266521736A069E4D057CB452A034F7C850C31

Here I'm asking for a hash using the number three as input parameter for the procedure that gives us the SHA-1 version hash. The procedure returns raw values (automatically converted to hex for us) . Valid input values are either raw or lob values, that's why the example uses the UTL_RAW.CAST_TO_RAW function to first convert the varchar2 value into a raw value. Comparing the generated hash value with the original hash value (stored somewhere) one can easily see if the data has been changed.

By the way if you don't have the documentation on hand you could always ask the database for the information about those supplied packages. For example I didn't remember the parameter for SHA-1 on the previous example so I used this query to find out what it was (DBMS_CRYPTO also supports md-4 and md-5 hashes):
select text from dba_source where name like'%DBMS_CRYPTO%';
...
-- PACKAGE NOTES
--
-- DBMS_CRYPTO contains basic cryptographic functions and
-- procedures. To use correctly and securely, a general level of
-- security expertise is assumed.
--
-- VARCHAR2 datatype is not supported. Cryptographic operations
-- on this type should be prefaced with conversions to a uniform
-- character set (AL32UTF8) and conversion to RAW type.
--
-- Prior to encryption, hashing or keyed hashing, CLOB datatype is
-- converted to AL32UTF8. This allows cryptographic data to be
-- transferred and understood between databases with different
-- character sets, across character set changes and between
-- separate processes (for example, Java programs).
--
---------------------------------------------------------------------------


-------------------------- ALGORITHM CONSTANTS ----------------------------
-- The following constants refer to various types of cryptographic
-- functions available from this package. Some of the constants
-- represent modifiers to these algorithms.
---------------------------------------------------------------------------

-- Hash Functions
HASH_MD4 CONSTANT PLS_INTEGER := 1;
HASH_MD5 CONSTANT PLS_INTEGER := 2;
HASH_SH1 CONSTANT PLS_INTEGER := 3;
...

there I have the information needed :)