\ufffd\t\t Cracking the Universal Product Code
\n\t\t\t by Count Nibble
\n\t\t\t —————<\/p>\n
Have you ever though of what fun you could have by altering that little set of
\nblack bars? If you were lucky enough, you might be able to slip a box of
\nindustrial size laundry detergent by that dizzy 16- year-old girl at the Safeway
\nand have the computer charge you the price of a pack of Juicy Fruit, or some
\nother such mischief. Well, to help you in your explo\ufffdrations of How To Screw
\nOver Others In This Grand Old Computerized World of Ours, I proudly present HOW
\nTO CRACK TO UPC CODE. Use the information contained herein as you will. You
\nwill need the file UPC.PIC, hopefully available from the same place you found
\nthis file. And so, let’s begin:<\/p>\n
When the lady at the corner market runs the package over the scanner (or
\nwhatever it is they do in your area), the computerized cash register reads the
\nUPC code as a string of binary digits.\tFirst it finds the “frame bars” – a
\nsequence of “101” (see A on picture). There are three sets of frame bars on any
\ngiven code…one on either side, and one in the center. These do nothing but
\nset off the rest of the data, and are the same on any UPC code. Next is the
\n“number system character” digit, which is encoded in leftside code (see later).
\nThis digit tells the computer what type of merchandise is being purchased. The
\ndigits and their meanings are:<\/p>\n
\t0\t– Ordinary grocery items. Bread, magazines, soup, etc.
\n\t2\t– Variable-weight items. Meats, fruits & veggies, etc.
\n\t3\t– Health items. Aspirin, bandaids, tampons, etc.
\n\t5\t– Cents-off coupon. (Not sure how this works).<\/p>\n
The next cluster of digits is the manufacturer number, again stored in
\nleftside code.\tTHere are five digits here all the time. Some numbers include
\n51000 for Campbell’s Soup, 14024 for Ziff-Davis publishing (Creative Computing,
\nA…), and 51051 for Infocom. The next five digits (after the frame bars) are
\nthe product\/size id number. The number for “The Hitchhiker’s Guide to the
\nGalaxy” from Infocom is 01191. These digits are stored in rightside code.
\nFinally there is the checksum, in rightside, which will be discussed later.<\/p>\n
Now, why are there two types of codes, leftside and rightside? That’s so the
\nperson at the checkout counter can slide the thing by the scanner any way she
\npleases. By having different codings for either side the computer can tell the
\nright value no matter how the digits are read in. \ufffd Here are the codes for the
\ndigits 0 through 9:<\/p>\n
Digit\t\tLeftside code\t\tRightside code
\n —–\t\t————-\t\t————–
\n\t0\t\t 0001101\t\t 1110010
\n\t1\t\t 0011001\t\t 1100110
\n\t2\t\t 0010011\t\t 1101100
\n\t3\t\t 0111101\t\t 1000010
\n\t4\t\t 0100011\t\t 1011100
\n\t5\t\t 0110001\t\t 1001110
\n\t6\t\t 0101111\t\t 1010000
\n\t7\t\t 0111011\t\t 1000100
\n\t8\t\t 0110111\t\t 1001000
\n\t9\t\t 0001011\t\t 1110100<\/p>\n
The more observant among you may have noticed that Rightside code is nothing
\nmore than logical-NOTed Leftside code, i.e., a 0 in Leftside is a 1 in Right-
\nside, and vice versa. Later on we will discuss another type called Reversed
\nRightside, in which the binary values in Rightside are reversed, meaning that
\n1110100 (9) in Rightside would be 0010111 in Reversed Rightside. RR is used
\nonly when there is an extra set of codes off to the right of the main code bars,
\nas with books and magazines.<\/p>\n
Now we see the hard part: how the checksum digit is encoded. Let’s try
\nworking out the checksum for “Hitchhiker’s Guide”.<\/p>\n
First, notice the Number System Character. Software is considered a Grocery
\nItem by UPC, so the NSC is 0 (zero). Next, Infocom’s Manufacturer’s Number is
\n51051, and the game’s id number is 01191. Good enough. Set together, these
\nnumbers look like this:<\/p>\n
\t0 51051 01191<\/p>\n
Now, take the digits of the code and write them on alternate lines, odd on one
\nline, even below, giving this:<\/p>\n
\t0 1 5 0 1 1
\n\t 5 0 1 1 9<\/p>\n
Now add each set of numbers:<\/p>\n
\t0+1+5+0+1+1 = 8
\n\t 5+0+1+1+9 = 16<\/p>\n
Multiply the first number (the ones created by adding the first, third, etc
\ndigits) by three:<\/p>\n
\t8×3 = 24<\/p>\n
And add that to the result of the other number (second, fourth, etc digits
\nadded together):<\/p>\n
\t24+16=40<\/p>\n
Subtract this from the next higher or equal multiple of 10 (40 in this case)<\/p>\n
\t40-40=0<\/p>\n
And the remainder, here 0 (zero), is the checksum digit.<\/p>\n
Now, what if there’s a set of other bars off to the side? For books, the
\nsequence is as follows:<\/p>\n
\tFive digits
\n\tStarts with 1011
\n\tIf (first digit is even) then sequence is L-RR-L-L-RR
\n \ufffd else sequence is RR-L-L-RR-L
\n\teach digit is separated with 01<\/p>\n
Therefore, the sequence for 29656 is:<\/p>\n
\t1011 0010011 01 0010111 01 0101111 01 0110001 01 0000101
\n\t 2L\t 9RR\t 6L \t5L\t 6RR<\/p>\n
and the sequence for 14032 is:<\/p>\n
\t1011 0110011 01 0100011 01 0001101 01 0100001 01 0010011
\n\t 1RR\t 4L\t 0L \t3RR\t 2L<\/p>\n
Naturally, all these bars are run together. There is no checksum.<\/p>\n
For magazines, the sequence is even more complex. There are two digits in
\neach bar, and the numbers usually run from 1-12, signifying the month.\tThe
\nfirst digits are encoded thusly:<\/p>\n
\tL if the digit is 1,4,5,8 or 9 and
\n\tRR if the digit is 2,3,6,7 or 0.<\/p>\n
The second digit is coded in L if it is even, and RR if it is odd. Therefore,
\n06 codes as:<\/p>\n
\t1011 0100111 01 0101111<\/p>\n
and 11 codes as:<\/p>\n
\t1011 0110011 01 0110011<\/p>\n
No checksum here, either, and the fields are again separated by 01.<\/p>\n
Well, that about does it for this explanation of how to crack the UPC codes.<\/p>\n
Use this information as you will, and forward any question to THE SPACE BAR,
\n505-265-5178, pw:BANZAI. Enjoy!<\/p>\n
\t– Count Nibble –<\/p>\n
