TRADE TIPS Access Cards: A Lesson in Mathematics H ave you ever tried to get a customer’s access card to work on his or her system, but the card number and/or the facility code is unknown? How do you recover this lost and vital information? Well, there are two ways — the manual way (pen, paper and math) or the automatic way (an app). The au- tomatic way is a great time-saver, but knowing how to do it by hand is essential to understand how the app works. Access cards come in a wide variety of formats and typically contain two pieces of information — the card number and the facility code (although some formats do not use facility codes). When the installer orders a box of cards or fobs, the format, card numbers and the facility code are known and expressed in the everyday base 10 numbering system. For example, let’s say we have a format of 26 bits HID standard, cards 40, 200-40, 299 and a facility code of 74. If that information matches the cards, then all is well. But if something is unknown and the access control system isn’t giving you this information when you badge the card at a reader, then you need to grab the binary or hexadecimal readout. Access cards store this information in binary format, not base 10. So the goal is to find the binary string that the unknown card is transmitting. Unfortunately, acquiring the binary string isn’t black and white. It’s based on the system you’re installing and whether or not it comes with a utility or feature in the soſtware that populates the information. There are several systems out there, so you’ll need to research how this part of the process is achieved for your particular system. Once you’ve acquired the binary string, it’s time to analyze. Let’s take the following string — 00100101010011101010100101. The first thing to take notice of is the bit length, which in this case is 26 (meaning there’s a total of 26 digits). For this example we’ll assume this string is 26 bits HID standard. Embedded in this array of ones and zeros are the card number and facility code (FC), as shown below. Figure 1. Once the Prox Card app has downloaded, open it. You’ll see a screen like the one shown here. Figure 2. Enter either the bi- nary string or the hex string followed by the system it will be using. Then hit “calcu- late,” and it calculates the math for you. parity bits don’t matter for this exercise, but, simply put, they’re there as a checksum for the entire string. All you need to do now is convert the two binary numbers into base 10. The facility code can be easily done by hand; how- ever, a calculator is advised for the card number (simply due to the length). As seen above, the facility code converts to 74. The card num- ber converts to 40,274 (which I got using a calculator). The manual process is great to learn so you understand how it works, but it’s not very practical out in the field, especially if the formatting is unknown. Fortunately, there is a quicker and more efficient method. Prox Card is an application you can use to do the math for you. Download the app from the Apple App Store or visit www. locksmithapps.com to get a direct link. Once it has downloaded, open the app. You’ll see a screen like the one in Figure 1. Enter either the binary string or the hex string followed Both the facility code and card number are now easily distin- guishable, sandwiched inside the parity bits. The values of the by the system it will be using. Then hit “calculate.” What was demonstrated above is now displayed on the screen (Figure 2). — Phil Domenici WWW.ALOA.ORG MARCH 2014 KEYNOTES 13
