Experiment 20: A Powerful Combination
204 Chapter 4
Another enhancement could be an additional 555 timer that is activated by
the asterisk button, and delivers power to the other chips for, say, a limited
period of 30 seconds, allowing you that much time to unlock the system. This
would eliminate the need to hold down the asterisk button while you enter
the unlocking code. A 555 timer can supply power to all the other chips, be-
cause they don’t use very much. I omitted this feature for the sake of simplicity.
Yet another enhancement, if you are security-crazed, is to go for a four-button
code. After all, the 74HC08 chip still has one unused AND gate. You could in-
sert that into the chain of the existing AND gates and wire it to another keypad
button of your choice.
Still another enhancement would be a way to change the code without unsol-
dering and resoldering wires. You can use the miniature sockets that I suggest-
ed in the heartbeat flasher project. These should enable you to swap around
the ends of your wires from the keypad.
And for those who are absolutely, positively, totally paranoid, you could fix
things so that entering a wrong code flips a second high-amperage relay
which supplies a massive power overload, melting your CPU and sending a
big pulse through a magnetic coil clamped to your hard drive, instantly turn-
ing the data to garbage (Figure 4-86). Really, if you want to protect informa-
tion, messing up the hardware has major advantages compared with trying
to erase data using software. It’s faster, difficult to stop, and tends to be per-
manent. So, when the Record Industry Association of America comes to your
home and asks to switch on your computer so that they can search for illegal
file sharing, just accidentally give them an incorrect unlocking code, sit back,
and wait for the pungent smell of melting insulation.
If you pursue this option, I definitely take no responsibility for the consequences.
On a more realistic level, no system is totally secure. The value of a hardware
locking device is that if someone does defeat it (for instance, by figuring out
how to unscrew your tamper-proof screws, or simply ripping your keypad out
of the computer case with metal shears), at least you’ll know that something
happened—especially if you put little dabs of paint over the screws to re-
veal whether they’ve been messed with. By comparison, if you use password-
protection software and someone defeats it, you may never know that your
system has been compromised.Figure 4-86. For those who are absolutely,
positively, totally paranoid: a meltdown/
self-destruct system controlled by a secret
key combination provides enhanced
protection against data theft or intrusions
by RIAA investigators asking annoying
questions about file sharing.