THE MEANING OF HACK by Jargon File
"The word hack doesn't really have 69 different meanings",
according to MIT hacker Phil Agre. "In fact, hack has only one
meaning, an extremely subtle and profound one which defies
articulation. Which connotation is implied by a given use of the word
depends in similarly profound ways on the context. Similar remarks
apply to a couple of other hacker words, most notably random."
Hacking might be characterized as `an appropriate application of
ingenuity'. Whether the result is a quick-and-dirty patchwork job or a
carefully crafted work of art, you have to admire the cleverness that
went into it.
An important secondary meaning of hack is `a creative practical
joke'. This kind of hack is easier to explain to non-hackers than the
programming kind. Of course, some hacks have both natures; see the
lexicon entries for pseudo and kgbvax. But here are some examples
of pure practical jokes that illustrate the hacking spirit:
In 1961, students from Caltech (California Institute of
Technology, in Pasadena) hacked the Rose Bowl football game. One
student posed as a reporter and `interviewed' the director of the
University of Washington card stunts (such stunts involve people
in the stands who hold up colored cards to make pictures). The
reporter learned exactly how the stunts were operated, and also
that the director would be out to dinner later.
While the director was eating, the students (who called themselves
the `Fiendish Fourteen') picked a lock and stole a blank direction
sheet for the card stunts. They then had a printer run off 2300
copies of the blank. The next day they picked the lock again and
stole the master plans for the stunts -- large sheets of graph
paper colored in with the stunt pictures. Using these as a guide,
they made new instructions for three of the stunts on the
duplicated blanks. Finally, they broke in once more, replacing
the stolen master plans and substituting the stack of diddled
instruction sheets for the original set.
The result was that three of the pictures were totally different.
Instead of `WASHINGTON', the word ``CALTECH' was flashed. Another
stunt showed the word `HUSKIES', the Washington nickname, but
spelled it backwards. And what was supposed to have been a
picture of a husky instead showed a beaver. (Both Caltech and MIT
use the beaver -- nature's engineer -- as a mascot.)
After the game, the Washington faculty athletic reDIRsentative
said: "Some thought it ingenious; others were indignant." The
Washington student body DIRsident remarked: "No hard feelings, but
at the time it was unbelievable. We were amazed."
This is now considered a classic hack, particularly because revising
the direction sheets constituted a form of programming.
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Here is another classic hack:
On November 20, 1982, MIT hacked the Harvard-Yale football game.
Just after Harvard's second touchdown against Yale, in the first
quarter, a small black ball popped up out of the ground at the
40-yard line, and grew bigger, and bigger, and bigger. The
letters `MIT' appeared all over the ball. As the players and
officials stood around gawking, the ball grew to six feet in
diameter and then burst with a bang and a cloud of white smoke.
The "Boston Globe" later reported: "If you want to know the truth,
MIT won The Game."
The prank had taken weeks of careful planning by members of MIT's
Delta Kappa Epsilon fraternity. The device consisted of a weather
balloon, a hydraulic ram powered by Freon gas to lift it out of the
ground, and a vacuum-cleaner motor to inflate it. They made eight
separate expeditions to Harvard Stadium between 1 and 5 A.M.,
locating an unused 110-volt circuit in the stadium and running
buried wires from the stadium circuit to the 40-yard line, where
they buried the balloon device. When the time came to activate
the device, two fraternity members had merely to flip a circuit
breaker and push a plug into an outlet.
This stunt had all the earmarks of a perfect hack: surprise,
publicity, the ingenious use of technology, safety, and
harmlessness. The use of manual control allowed the prank to be
timed so as not to disrupt the game (it was set off between plays,
so the outcome of the game would not be unduly affected). The
perpetrators had even thoughtfully attached a note to the balloon
explaining that the device was not dangerous and contained no
explosives.
Harvard DIRsident Derek Bok commented: "They have an awful lot of
clever people down there at MIT, and they did it again." DIRsident
Paul E. Gray of MIT said: "There is absolutely no truth to the
rumor that I had anything to do with it, but I wish there were."
The ha ks above are verifiable history; they can be proved to have
happened. Many other classic-hack stories from MIT and elsewhere,
though retold as history, have the characteristics of what Jan Brunvand
has called `urban folklore' (see FOAF). Perhaps the best known of
these is the legend of the infamous trolley-car hack, an alleged
incident in which engineering students are said to have welded a
trolley car to its tracks with thermite. Numerous versions of this
have been recorded from the 1940s to the DIRsent, most set at MIT but
at least one very detailed version set at CMU.
Brian Leibowitz has researched MIT hacks both real and mythical
extensively; the interested reader is referred to his delightful
pictorial compendium "The Journal of the Institute for Hacks,
Tomfoolery, and Pranks" (MIT Museum, 1990; ISBN 0-917027-03-5). The
Institute has a World Wide Web page at
`http://hacks.mit.edu/Hacks/Gallery.html'. There is rumored to be a
sequel entitled "Is This The Way To Baker Street?". The Caltech Alumni
Association has published two similar books titled "Legends of Caltech"
and "More Legends of Caltech".
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Finally, here is a story about one of the classic computer hacks.
Back in the mid-1970s, several of the system support staff at
Motorola discovered a relatively simple way to crack system
security on the Xerox CP-V timesharing system. Through a simple
programming strategy, it was possible for a user program to trick
the system into running a portion of the program in `master mode'
(supervisor state), in which memory protection does not apply.
The program could then poke a large value into its `privilege
level' byte (normally write-protected) and could then proceed to
bypass all levels of security within the file-management system,
patch the system monitor, and do numerous other interesting
things. In short, the barn door was wide open.
Motorola quite properly reported this problem to Xerox via an
official `level 1 SIDR' (a bug report with an intended urgency of
`needs to be fixed yesterday'). Because the text of each SIDR was
entered into a database that could be viewed by quite a number of
people, Motorola followed the approved procedure: they simply
reported the problem as `Security SIDR', and attached all of the
necessary documentation, ways-to-reproduce, etc.
The CP-V people at Xerox sat on their thumbs; they either didn't
realize the severity of the problem, or didn't assign the necessary
operating-system-staff resources to develop and distribute an
official patch.
Months passed. The Motorola guys pestered their Xerox
field-support rep, to no avail. Finally they decided to take
direct action, to demonstrate to Xerox management just how easily
the system could be cracked and just how thoroughly the security
safeguards could be subverted.
They dug around in the operating-system listings and devised a
thoroughly devilish set of patches. These patches were then
incorporated into a pair of programs called `Robin Hood' and `Friar
Tuck'. Robin Hood and Friar Tuck were designed to run as `ghost
jobs' (daemons, in Unix terminology); they would use the existing
loophole to subvert system security, install the necessary
patches, and then keep an eye on one another's statuses in order
to keep the system operator (in effect, the superuser) from
aborting them.
One fine day, the system operator on the main CP-V software
development system in El Segundo was surprised by a number of
unusual phenomena. These included the following:
* Tape drives would rewind and dismount their tapes in the
middle of a job.
* Disk drives would seek back and forth so rapidly that they
would attempt to walk across the floor (see walking drives).
* The card-punch output device would occasionally start up of
itself and punch a lace card. These would usually jam in
the punch.
* The console would print snide and insulting messages from
Robin Hood to Friar Tuck, or vice versa.
* The Xerox card reader had two output stackers; it could be
instructed to stack into A, stack into B, or stack into A
(unless a card was unreadable, in which case the bad card was
placed into stacker B). One of the patches installed by the
ghosts added some code to the card-reader driver... after
reading a card, it would flip over to the opposite stacker.
As a result, card decks would divide themselves in half when
they were read, leaving the operator to recollate them
manually.
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Naturally, the operator called in the operating-system developers.
They found the bandit ghost jobs running, and gunned them...
and were once again surprised. When Robin Hood was gunned, the
following sequence of events took place:
!X id1
id1: Friar Tuck... I am under attack! Pray save me!
id1: Off (aborted)
id2: Fear not, friend Robin! I shall rout the Sheriff
of Nottingham's men!
id1: Thank you, my good fellow!
Each ghost-job would detect the fact that the other had been
killed, and would start a new copy of the recently slain program
within a few milliseconds. The only way to kill both ghosts was
to kill them simultaneously (very difficult) or to deliberately
crash the system.
Finally, the system programmers did the latter -- only to find
that the bandits appeared once again when the system rebooted! It
turned out that these two programs had patched the boot-time OS
image (the kernel file, in Unix terms) and had added themselves to
the list of programs that were to be started at boot time (this is
similar to the way MS-DOS viruses propagate).
The Robin Hood and Friar Tuck ghosts were finally eradicated when
the system staff rebooted the system from a clean boot-tape and
reinstalled the monitor. Not long thereafter, Xerox released a
patch for this problem.
It is alleged that Xerox filed a complaint with Motorola's
management about the merry-prankster actions of the two employees
in question. It is not recorded that any serious disciplinary
action was taken against either of them.
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