4 ms·

> Faraday bags exist (SLNT, Mission Darkness, etc.) - they block all RF signals They really don’t. “Blocking” RF really isn’t a thing. RF can be attenuated, b

> Faraday bags exist (SLNT, Mission Darkness, etc.) - they block all RF signals They really don’t. “Blocking” RF really isn’t a thing. RF can be attenuated, but it is quite a complicated problem to solve. Have you tried any of these bags?

next_xibalba 9mo ago
So they don’t effectively block communication to and from the device? Or they don’t block all RF? Because the former seems to qualify as working, while the latter seems irrelevant. Or the only sometimes block communication to/from the device?
- kube-system 9mo ago
  > So they don’t effectively block communication to and from the device? That is impossible to know without knowing the characteristics of the signal, noise, attenuation performance, sensitivity of the receiver, and other environmental conditions. > Or they don’t block all RF? They definitely don’t. If you want to attenuate an RF signal, you need to do RF engineering. There are products to help people do this (eg RF test enclosure), but they aren’t marketed as “blocking RF” because that is nonsensical. The products that advertise as “blocking RF” without any real specifications are unsuitable for serious RF engineering, they are primarily sold to conspiracy theorists, hypochondriacs, etc.
  - refulgentis 9mo ago
    >> So they don’t effectively block communication to and from the device? > That is impossible to know without knowing the characteristics of the signal Do you dispute that de facto these products work?
    - kube-system 9mo ago
      Yes I have spent thousands of dollars and months testing them. You can cut off GPS and high frequency cell spectrum pretty easily. Most cell spectrum is effectively attenuated by good quality professional RF enclosures designed for those frequencies. 2.4 ghz signals like wifi (with good quality radios) are hard to attenuate to the point where they can’t connect to other radios nearby, even with very expensive RF test enclosures. If you’re trying to block against an unknown threat you are fucked. If someone wanted to back door a baseband they’d probably make it transmit at low speeds and low frequencies to be resistant to attenuation.
      - refulgentis 9mo ago
        Jesus. That sucks. Thanks for sharing, fascinating stuff.
      - digiown 9mo ago
        What kind of RF can travel through a few mm of metal?
        kube-system 9mo ago
        If you blindly “put metal around” an antenna, most of the time, you have just created another antenna! Go put a phone in a filing cabinet and call it. It will ring.
    - bigyabai 9mo ago
      I will, I've got two and neither one can shut off a longwave FM radio.
- avadodin 9mo ago
  It is only irrelevant because devices made in this century put a lot of work into not transmitting outside of the intended frequencies. My old Nokia would smash the whole range of AM/FM and UHF bands. I don't know about higher frequencies that could escape one of these cages intended to block WiFi/5G/GPS but it is possible in theory and then it would be likely a backdoor that only becomes active when no signal can be detected.
ssl-3 9mo ago
Way back in the flip phone days, I had evil tracking software on my corpo phone for a time. I didn't mind that they knew where I was when I was being paid, but I had issues with abuse by one particular manager (who was more my equal than my boss, but nevermind that). This tracking software could be disabled with a couple of button pushes, or the phone simply turned off, but these action generated alerts that were sent home to the mothership. I did not like this aspect at all. So I bought a little Faraday bag from somewhere in China -- back then, probably from DealExtreme. It fit the phone so well that it seemed like it must have been made for that specific model (even though it almost certainly was not). Inside, it had two compartments: One that encapsulated the device well-enough with conductive fabric, and another that was outside of (and adjacent to) that envelope, which just protected the phone from things like incidental abrasions. I used it as an every-day phone case. When I wanted the phone to work, I used the non-shielded part. If I wanted the phone to not work, then I used the shielded compartment instead. In imprecise practical terms, this bag blocked successful RF communications. (And I knew this to be true, because I also had access to the mothership's web interface and could review the tracking data for myself and my coworkers.) --- I can accept that "blocked" is not the most-precise term. In a way that is similar to many other things, a valid and accurate technical description of what was achieved would require additional precision. But such precision is not always necessary in order to succinctly have words convey their desired intent, and I don't think it's required here for OP's intent to be understood.
- kube-system 9mo ago
  Maybe it worked with less sensitive radios back in the day. I have done experiments on recent devices and it’s very difficult. I was successful in attenuating cell service with a $XXXX test enclosure, but not 2.4Ghz WiFi. Maybe blocking cell service is good enough for your use case, but if you’re trying to protect against an APT you’re probably half-way closing the vulnerability.

next_xibalba 9mo ago

So they don’t effectively block communication to and from the device? Or they don’t block all RF? Because the former seems to qualify as working, while the latter seems irrelevant. Or the only sometimes block communication to/from the device?

kube-system 9mo ago
> So they don’t effectively block communication to and from the device? That is impossible to know without knowing the characteristics of the signal, noise, attenuation performance, sensitivity of the receiver, and other environmental conditions. > Or they don’t block all RF? They definitely don’t. If you want to attenuate an RF signal, you need to do RF engineering. There are products to help people do this (eg RF test enclosure), but they aren’t marketed as “blocking RF” because that is nonsensical. The products that advertise as “blocking RF” without any real specifications are unsuitable for serious RF engineering, they are primarily sold to conspiracy theorists, hypochondriacs, etc.
- refulgentis 9mo ago
  >> So they don’t effectively block communication to and from the device? > That is impossible to know without knowing the characteristics of the signal Do you dispute that de facto these products work?
  - kube-system 9mo ago
    Yes I have spent thousands of dollars and months testing them. You can cut off GPS and high frequency cell spectrum pretty easily. Most cell spectrum is effectively attenuated by good quality professional RF enclosures designed for those frequencies. 2.4 ghz signals like wifi (with good quality radios) are hard to attenuate to the point where they can’t connect to other radios nearby, even with very expensive RF test enclosures. If you’re trying to block against an unknown threat you are fucked. If someone wanted to back door a baseband they’d probably make it transmit at low speeds and low frequencies to be resistant to attenuation.
    - refulgentis 9mo ago
      Jesus. That sucks. Thanks for sharing, fascinating stuff.
    - digiown 9mo ago
      What kind of RF can travel through a few mm of metal?
      - kube-system 9mo ago
        If you blindly “put metal around” an antenna, most of the time, you have just created another antenna! Go put a phone in a filing cabinet and call it. It will ring.
  - bigyabai 9mo ago
    I will, I've got two and neither one can shut off a longwave FM radio.
avadodin 9mo ago
It is only irrelevant because devices made in this century put a lot of work into not transmitting outside of the intended frequencies. My old Nokia would smash the whole range of AM/FM and UHF bands. I don't know about higher frequencies that could escape one of these cages intended to block WiFi/5G/GPS but it is possible in theory and then it would be likely a backdoor that only becomes active when no signal can be detected.

ssl-3 9mo ago

Way back in the flip phone days, I had evil tracking software on my corpo phone for a time. I didn't mind that they knew where I was when I was being paid, but I had issues with abuse by one particular manager (who was more my equal than my boss, but nevermind that). This tracking software could be disabled with a couple of button pushes, or the phone simply turned off, but these action generated alerts that were sent home to the mothership. I did not like this aspect at all. So I bought a little Faraday bag from somewhere in China -- back then, probably from DealExtreme. It fit the phone so well that it seemed like it must have been made for that specific model (even though it almost certainly was not). Inside, it had two compartments: One that encapsulated the device well-enough with conductive fabric, and another that was outside of (and adjacent to) that envelope, which just protected the phone from things like incidental abrasions. I used it as an every-day phone case. When I wanted the phone to work, I used the non-shielded part. If I wanted the phone to not work, then I used the shielded compartment instead. In imprecise practical terms, this bag blocked successful RF communications. (And I knew this to be true, because I also had access to the mothership's web interface and could review the tracking data for myself and my coworkers.) --- I can accept that "blocked" is not the most-precise term. In a way that is similar to many other things, a valid and accurate technical description of what was achieved would require additional precision. But such precision is not always necessary in order to succinctly have words convey their desired intent, and I don't think it's required here for OP's intent to be understood.

kube-system 9mo ago
Maybe it worked with less sensitive radios back in the day. I have done experiments on recent devices and it’s very difficult. I was successful in attenuating cell service with a $XXXX test enclosure, but not 2.4Ghz WiFi. Maybe blocking cell service is good enough for your use case, but if you’re trying to protect against an APT you’re probably half-way closing the vulnerability.