Everyone encounters the
UPC nowadays. You know, it's that set of black bars
you see on virtually every product whenever you go to the
grocery store, to
buy a book or a magazine, or even to buy
software (assuming that you do, indeed,
BUY your
software). Have you ever though of what fun you could have by altering
that little set of black bars? If you were
lucky enough, you might be able to
slip a box of
industrial size laundry detergent by that dizzy 16- year-old girl
at the
Safeway and have the computer charge you the price of a pack of
Juicy
Fruit, or some other such mischief. Well, to help you in your explorations of
How To Screw Over Others In This Grand Old Computerized World of Ours, I proudly
present
HOW TO CRACK TO UPC CODE. Use the information contained herein as you
will. And so, let's
begin:
When the lady at the
corner market runs the package over the
scanner (or whatever
it is they do in your area), the computerized
cash register reads the
UPC
code as a
string of
binary digits. First it finds the "frame bars" - a
sequence
of "101". There are three sets of frame bars on any given
code...one on either
side, and one in the
center. These do nothing but set off the rest of the data,
and are the same on any
UPC code. Next is the "number system character"
digit,
which is encoded in
leftside code (see later). This digit tells the computer
what type of merchandise is being purchased. The digits and their meanings are:
0 - Ordinary
grocery items. Bread, magazines, soup, etc.
2 -
Variable-weight items. Meats, fruits & veggies, etc.
3 -
Health items. Aspirin, bandaids, tampons, etc.
5 -
Cents-off coupon. (Not sure how this works).
The next cluster of digits is the
manufacturer number, again stored in
leftside
code. There are five digits here all the time. Some numbers include 51000 for
Campbell's Soup, 14024 for
Ziff-Davis publishing (Creative Computing, A...),
and 51051 for
Infocom. The next five digits (after the
frame bars) are the
product/
size id number. The number for "
The Hitchhiker's Guide to the Galaxy"
from
Infocom is 01191. These digits are stored in
rightside code. Finally
there is the
checksum, in
rightside, which will be discussed later.
Now, why are there two types of codes,
leftside and
rightside? That's so the
person at the checkout counter can slide the thing by the
scanner any way she
pleases. By having different codings for either side the computer can tell the
right value no matter how the
digits are read in. Here are the
codes for the
digits 0 through 9:
Digit Leftside code Rightside code
0 0001101 1110010
1 0011001 1100110
2 0010011 1101100
3 0111101 1000010
4 0100011 1011100
5 0110001 1001110
6 0101111 1010000
7 0111011 1000100
8 0110111 1001000
9 0001011 1110100
The more
observant among you may have noticed that
Rightside code is nothing
more than logical-NOTed Leftside code, i.e., a 0 in Leftside is a 1 in Right-
side, and vice versa (0 -> ~0 = 1). Later on we will discuss another type called
Reversed Rightside, in which the
binary values in
Rightside are reversed,
meaning that 1110100 (9) in
Rightside would be 0010111 in
Reversed Rightside.
RR is used only when there is an extra set of
codes off to the right of the
main code bars, as with
books and
magazines.
Now we see the hard part: how the
checksum digit is
encoded. Let's try working
out the checksum for "
Hitchhiker's Guide".
First, notice the
Number System Character.
Software is considered a Grocery
Item by
UPC, so the NSC is 0 (zero). Next,
Infocom's
Manufacturer's Number
is 51051, and the game's id number is 01191. Good enough. Set together, these
numbers look like this:
0
51051 01191
Now, take the digits of the code and write them on alternate lines, odd on one
line, even below, giving this:
0
1 5 0 1 1
5
0 1 1 9
Now
add each set of numbers:
0+1+5+0+1+1
= 8
5+0+1+1+9
= 16
Multiply the first number (the ones created by adding the first, third, etc
digits) by three:
8
x 3 = 24
And
add that to the
result of the other number (second, fourth, etc digits
added together):
24
+ 16 = 40
Subtract this from the next higher or equal
multiple of 10 (40 in this case)
40
- 40 = 0
And the
remainder, here 0 (zero), is the
checksum digit.
Now, what if there's a set of other
bars off to the side? These are
encoded
in another
format which uses
Reversed Rightside (as described above) instead
of standard
Rightside. For
books, the sequence is as follows:
Five digits
Starts with 1011
If (first digit is even) then
sequence is L-RR-L-L-RR
else
sequence is RR-L-L-RR-L
each digit is separated with 01
Therefore, the
sequence for 29656 is:
1011 0010011 01 0010111 01 0101111 01 0110001 01 0000101
2L
9RR
6L
5L
6RR
and the sequence for 14032 is:
1011 0110011 01 0100011 01 0001101 01 0100001 01 0010011
1RR
4L
0L
3RR
2L
Naturally, all these bars are run together. There is no
checksum.
For
magazines, the
sequence is even more
complex. There are two
digits
in each
bar, and the numbers usually run from 1-12, signifying the
month.
The first digits are
encoded thusly:
L if the digit is 1,4,5,8 or 9 and
RR if the digit is 2,3,6,7 or 0.
The second digit is coded in L if it is even, and RR if it is odd. Therefore,
06 codes as:
1011 0100111 01 0101111
and 11 codes as:
1011 0110011 01 0110011
No
checksum here, either, and the
fields are again separated by 01.
props to:
Count Nibble and
The Pirate's Hollow for collecting great information