Cracking the Universal Product Code

by Count Nibble

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. You will need the file UPC.PIC, hopefully available from the same place you found this file. 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" (see A on picture). 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...

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