Signals Defense With Faraday Bags & Flipper Zero

Published: 2023-05-16. Last Updated: 2023-05-16 14:06:06 UTC
by Jesse La Grew (Version: 1)
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There are situations where it is desired to block signals between devices. Commonly scenarios are when traveling, in a location of uncertain safety, or otherwise concerned with data privacy and geolocation. I was curious how well a faraday bags and similar products protected wireless communications. A more common purchase these days are wallets that can help to protect against RFID skimming of credit card data [1].

Here were the scenarios tested using some faraday bags (Haftigts) [2] and in some cases a Flipper Zero [3]:

Wireless Communications Scenario / Device
125 kHz RFID HID proximity card, read with Flipper Zero [4]
HID proximity fob, read with Flipper Zero
NFC Credit Card, read with Flipper Zero [5]
Bluetooth Phone in bag and bluetooth earbuds
WiFi (802.11) Phone in bag used as hotspot, laptop connected to hotspot
Celluar Phone in bag, another cellular phone used to call it

Extensive testing was done done using a variety of faraday bags and devices.

Scenario Testing Process
HID proximity card HID proximity card placed into bag
Bag closed and sealed
Flipper Zero placed on top of bag over card location
Flipper Zero used to read 125 kHz RFID data
HID proximity fob HID proximity fob placed into bag
Bag closed and sealed
Flipper Zero placed on top of bag over card location
Flipper Zero used to read 125 kHz RFID data
Credit Card Credit card placed into bag
Bag closed and sealed
Flipper Zero placed on top of bag over card location
Flipper Zero used to read NFC data
Bluetooth iPhone connected to iPods via Bluetooth
iPhone playing audio content
iPhone placed into bag
Listened for audio disruptions
WiFi (802.11) Android phone with hotspot turned on
Windows device connected to hotspot
Continuous ping set to 8.8.8.8
Android phone placed into bag
Ping reviewed for disruptions
Cellular iPhone placed into bag
Android phone used to call iPhone

The results for these different tests were pretty quick. For the Flipper Zero tests, either the data could be read or it couldn't. For bluetooth and wifi, it was just waiting to see how the signal changed. Now for the results:

Scenario Result
HID proximity card Fail
(Flipper Zero was able to read the data)
HID proximity fob Fail
(Flipper Zero was able to read the data)
Credit Card Success
(Flipper Zero was unable to read the data)
Bluetooth Limited Success
(Audio signal cut in and out, heavily impacted by proper sealing of the bag)
WiFi (802.11) Success
(Wireless network was quickly disconnected and unable to be seen from mobile hotspot feature)
Cellular Success
(iPhone was unable to receive phone call, Android phone was directed straight to voicemail)

From the testing, there were a few takeaways:

  • Test to make sure your protections are effective
  • Make sure to follow instructions - Bluetooth audio was very functional with a partially closed bag
  • When in doubt, turn off features, or devices, if not needed and when in a space of uncertain safety

For some of these attacks, someone would need very close proximity to complete a successful attack. In the case of testing using the Flipper Zero, the reader was physically sitting on top of the bag and that would be much more challenging for someone to do in a real world situation.


[1] https://www.zdnet.com/article/do-rfid-blocking-cards-actually-work-my-flipper-zero-revealed-the-truth/
[2] https://www.amazon.com/dp/B0BHSH8BLR?ref=ppx_yo2ov_dt_b_product_details&th=1
[3] https://flipperzero.one/
[4] https://docs.flipperzero.one/rfid
[5] https://docs.flipperzero.one/nfc

--
Jesse La Grew
Handler

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ISC Stormcast For Tuesday, May 16th, 2023 https://isc.sans.edu/podcastdetail/8498

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