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D0wn och D1rty med Wiegand

A few months ago, we published a history of where Weigand came from and a XCHARXlight-on-technical-detailsXCHARX overview of how it works. For those of us that are more engineer-y, it left a bit to be desired. For me in particular, I recently was doing some low level work with one of my engineers. We were monitoring the lines from a badge reader and I couldnXCHARXt recall what the spec for the pulse width should be. For most people, this level of detail is overkill, but since for those of you who get down and dirty with D0/D1 of Wiegand, this post is for you.

Som du kanske kommer ihåg från vårt tidigare inlägg används Wiegand utbytbart för att beskriva ett antal saker - en elektronisk effekt, ett åtkomstkort, lite ström

Wiegand
Wiegand - Det bekväma åtkomstkontrollgränssnittet förklaras i detalj i detta inlägg.

associated with a card, or a specific reader-to-card interface. We are going to be referring to Wiegand as the signal that comes from an access control reader, out of the Data 0 (D0) and Data 1 (D1) lines. This data is interpreted as an access card number by parsing the bit stream.

Wiegand-standarden är bara en de facto-standard, men det finns en Security Industry Association (SIA) dokument "Åtkomstkontroll Standardprotokoll för läsargränssnittet 26-bit Wiegand (tm)” which describes an agreed standard that should work with all manufacturers’ panels. Some of the basic information found in this document is found below.

When a reader with a Wiegand interface is hooked up to an access panel, it generally includes 6 lines with the below color scheme, which interfaces with the back end access panel.

Wiegand Wiring
D0 (grön) och D1 (vit) utgångar är nästan universellt färgade Wiegand-läsare.

Back when Telaeris was developing our XPressProx mobile proximity reader to read HID Prox cards, we needed to demodulate the data directly from the RF signal (*). Once we decoded this signal, the data was pushed both over a USB connection as well driving the signal as over standard D0/D1 Wiegand lines. When we hooked up our Agilent 54622D Oscilloscope to the data lines and presented different cards to the reader, these are examples of what we saw:

26bit
26 bitutmatning
26 utgångsbitar 10000000100000010111001011 
   paritet även 1            paritet udda 1 
                00000001 Facility = 1    
          BadgeID = 741 0000001011100101 
36bit
36 bitutmatning
 36 utgångsbitar 011011001011001000100101101011100101 
37bit
37 bitutmatning
37 utgångsbitar 0001001000000011111101000001011001000

The 26 bit card is parsed out for you to see as the bit format is almost universally standard. The 36 and 37 bit cards are part of HIDXCHARXs corporate 1000 line, which often mix up the location of the bits in weird and wonderful ways. The security in these cards is often simply that it is difficult to know how a bit stream might be parsed. These bitstreams can come in a variety of lengths, all the way up to 200 for some US Government PIV cards.

Om du är intresserad av vad som händer på RF-nivå för HID-stil prox-kort, skicka mig ett mail.

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