Since its 14th edition, Defcon badges have gone electronic. Hardware wizard Joe Grand (he and I both worked at @stake a long time ago, though in different offices) creates these masterpieces and unleashes them on the thousands of people who descend upon Las Vegas every year for this oldest of the US hacker conferences, now in its 18th incarnation.
Befitting this conference, the badges have all sorts of hidden capabilities, easter eggs, etc. One of Defcon's many challenges is to find these backdoors. This year's badge is no exception. Sporting an LCD panel for the first time ever, pressing the badge's buttons causes all sorts of cryptic (and some not so cryptic) behavior.
One of the badge's challenges is to crack "Ninja mode" which you have to enable by picking an electronic lock consisting of fifteen tumblers, each one with three states (for a total of over 14million combinations).
I had fun with this one. I was making slow, steady progress until I thought of exploring the Defcon CD... Bingo! Joe was thoughtful enough to include a full development environment for the card, as well as the source code to the firmware! From that point "hacking" became a simple exercise in reverse engineering the code. I won't give the key away but I will say that Wolfram|Alpha proved very useful for quick conversions between binary, trinary, and hexadecimal.
In retrospect I should have looked at that CD much earlier :-)