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Hoy hoy!
I had an idea today for a device which i plan to make and bring with me to Defcon2600 on the second of October (i would feel weird going without having anything to show/offer, especially as it would be my first time)
Basically, it will be an RFID repeater in the form/shape of a plastic sign.
The sign will say something along the lines of 'Please close this door behind you'.
Within the sign will be an RFID antenna (similar in design to Henryk's diode receiver), and some basic circuitry to take and amplify this signal.
It will probably be powered by several button batteries, and needs to have a transmit range of at least 20 meters.
I'm concerned about the replayed signal effecting the communication between the tag/reader, so it may have to have a few seconds of delay - or transmit on a different frequency from what it listens on. Perhaps a blue tooth chip/antenna could be used to transmit..
I would prefer to keep the transmitted signal as unchanged from the original as possible, so it could be used in conjunction with a proxmark/proxpick.
What do you guys think about such a device? Purely as a proof-of-concept device to show people/manufacturers that the saving grace of RFID security - the small proximity between reader/tag - is not good enough.
Has anything like this been made/demonstrated in the past? I've heard it talked about before, but i've never actually seen such a device.
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This can probably be done mostly with off-the-shelf parts. My diode receiver outputs an audio signal, my load modulator needs an audio signal as input, and there are several commercial solutions for relaying audio signals on any carrier medium you'd like (infrared, proprietary 2.4GHz, bluetooth 2.4GHz, 433MHz, etc.). All you need in addition is some 125kHz carrier generator to power up the tag. You'll either have to provide this one yourself (e.g. at HAR I used a Hitag2 reader) or maybe, for greater hack value, use a second door for that, opening two doors with one card swipe (provided the card has access to both doors).
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Ahh, that's a great idea!
Capture with your diode receiver Henryk, modulate with some bluetooth AD2P thingy, pick it up on a laptop with a bluetooth dongle or anything else which can use bluetooth mics (iPhone, etc) and you're done!
I wasn't actually going to put anything in to provide the carrier Henryk - it was just going to sniff the communications between an existing card reader and it's tag. An attacker would simply place the sign next to the reader and then pick up the conversation from his car.
The real challenge is going to be making a highly sensitive antenna, and powering the bluetooth transmitter with just a few tiny batteries.
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