Credit cards: more business logic

Checksums!

Another seldom-known attribute
Change in business logic
Go right to left
Add them up: "odd" digits as is, "even" digits +10, -9 if > 10
Must be a multiple of 10

Old vs. new

Why catch it early? (automated attack)
Old: application logic, shared module
Best of the old (app): SELECT cc_checksum(..)
Best of the old (dba): trigger
New: domain function, all in one place


CREATE OR REPLACE FUNCTION validate_ccnumber(VARCHAR) 
RETURNS BOOLEAN AS '
DECLARE
  mynumber ALIAS FOR $1;
BEGIN

IF length(mynumber) != 16 THEN
  RAISE EXCEPTION \'Credit card numbers must be 16 digits long\';
END IF;


IF cc_checksum(mynumber) THEN
  RAISE EXCEPTION \'Invalid credit card number: checksum failed\n';
END IF;


RETURN TRUE;
END;
' LANGUAGE plpgsql;