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Testing Phone-Sized Faraday Bags

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Re: Testing Phone-Sized Faraday Bags

#191

Post by Johnythree »

formerly_proven wrote: post #90
willis936 wrote: post #44

Earlier quoted context omitted.

Microwave-ovens definitely don't leak below 2.4 GHz. Any frequency above that is a non-issue for microwave-oven operator safety. It also wouldn't be an issue for any communication device transmitting below 2.4 GHz. If you want to shut down 5 GHz communication then a microwave-oven would be leaky. 60 GHz: it shouldn't matter since it needs LoS anyway. Also, remember to ground your faraday cages.

The width of the area around microwave doors looks suspiciously close to lambda/4 for 2.4 GHz (~3 cm) on pretty much every microwave I've ever seen - I'd almost be surprised if that construction isn't tuned to reflect 2.4 GHz, which would make it a very leaky container at say 0.9/1.8 GHz.

Yes, microwave ovens use a tuned slot to seal the door. It's basically a half-wave stub.

Re: Testing Phone-Sized Faraday Bags

#192

Post by Johnythree »

tgb wrote: post #17

Interesting results. The article states that Faraday cages are no directional. My physics 101 understanding of them was otherwise. You show they work by integrating over the surface of the cage and saying that's equal to the charge within the surface. But you don't say it's equal to the charge outside. Indeed it couldn't possible, since that charge could be light-years away and steady state would never be achieved. N…

Building an effective Faraday Screen is surprisingly difficult:

There are three completely different scenarios, blocking electrostatic fields, blocking RF energy, and blocking alternating magnetic fields.

The first can be achieved by a thin conductive screen (eg brass mesh with soldered seams), the second by thick copper sheet (with bolted seams) and the third requires thick magnetic material (eg iron or nu-metal).

Re: Testing Phone-Sized Faraday Bags

#194

Post by usefulcat »

joshspankit wrote: post #182
gangstead wrote: post #158

Earlier quoted context omitted.

Sounds like what Consumer Reports does across various fields.

It’s all well and good until you get enough clout that a bad actor offers you a very large cheque to rig the game.

Is this a veiled accusation against CR? If so I’d appreciate some specifics. If not, I’ll just mention that AFAIK CR has always foregone all advertising, specifically to avoid such conflicts of interest.

Re: Testing Phone-Sized Faraday Bags

#195

Post by seanhunter »

One thing that most people should use a Faraday pouch for (in my opinion) is storing your key fobs if your vehicle uses keyless ignition with a fob. This prevents a very common relay attack which is to stand with a laptop by someone's front door and relay the keyfob signal between the keys (somewhere inside the person's house) and the car. For people who live in cities where you park on the street (as I do) it's extra-convenient for thieves in that most cars will flash some lights to say the alarm is disabled so the thieves know which car they just unlocked.

Re: Testing Phone-Sized Faraday Bags

#196

Post by skunkworker »

seanhunter wrote: post #195

One thing that most people should use a Faraday pouch for (in my opinion) is storing your key fobs if your vehicle uses keyless ignition with a fob. This prevents a very common relay attack which is to stand with a laptop by someone's front door and relay the keyfob signal between the keys (somewhere inside the person's house) and the car. For people who live in cities where you park on the street (as I do) it's extr…

I was also thinking about this, after seeing this reddit thread of a woman putting a device in front of a doorbell.

https://www.reddit.com/r/whatisthisthing/comments/r7kb03/my_...

Re: Testing Phone-Sized Faraday Bags

#197

Post by fsflover »

effie wrote: post #188
fsflover wrote: post #93

Earlier quoted context omitted.

They have the schematics [0,1] for these devices and even X-rays [1] for Librem 5. Also, anti-interdiction services for the latter [2]. [0] https://wiki.pine64.org/index.php/PinePhone#PinePhone_board_... [1] https://source.puri.sm/Librem5/community-wiki/-/wikis/Freque... [2] https://puri.sm/posts/anti-interdiction-services/

Isn't this rather a security theater for the more naive prospective buyers? Even if the device is verified to comply with high-level schematics, it still may not comply on the micro-level. There is the problem with all modem chips being able to access/control phone memory and being potentially controllable by the mobile network operator. How are we going to verify this vulnerability has been removed?

If you want to go this deep, consider this: https://www.crowdsupply.com/sutajio-kosagi/precursor. See also: https://news.ycombinator.com/item?id=27897975.

Re: Testing Phone-Sized Faraday Bags

#198

Post by seanhunter »

skunkworker wrote: post #196
seanhunter wrote: post #195

One thing that most people should use a Faraday pouch for (in my opinion) is storing your key fobs if your vehicle uses keyless ignition with a fob. This prevents a very common relay attack which is to stand with a laptop by someone's front door and relay the keyfob signal between the keys (somewhere inside the person's house) and the car. For people who live in cities where you park on the street (as I do) it's extr…

I was also thinking about this, after seeing this reddit thread of a woman putting a device in front of a doorbell. https://www.reddit.com/r/whatisthisthing/comments/r7kb03/my_...

Yeah a work colleague had his car stolen and his door cam recorded the thieves kind of waving a laptop about in front of it. I guess the antenna they use is highly directional so you have to get it just right to trigger.

The apple watch unlock feature in recent macOs versions apparently avoids this relay attack by using a high-precision timer so they know (given the speed of light) that the watch is very close and the signal could not be relayed from a watch that's further away by a mitm (because the timestamp would be too old). I guess car keyfobs don't do this kind of thing because the electronics are intentionally quite primitive to avoid excessive battery drain.

Re: Testing Phone-Sized Faraday Bags

#199

Post by refurb »

habi wrote: post #177
BenjiWiebe wrote: post #147

Earlier quoted context omitted.

X-rays _are_ electromagnetic radiation.

Of course the are, but - if I'm correct - they don't produce an electromagnetic field. And are not shielded by a bit of mesh wire (I work with desktop microCT machines...).

X-rays are the exact same thing as any other electromagnetic radiation, just at a different frequency.

Generally a mesh can block an EMR signal if the holes are < 1/2 wavelength in size. X-rays have nanometer wavelengths so the mesh wouldn’t even be visible to the naked eye.

Re: Testing Phone-Sized Faraday Bags

#200

Post by rrmoelker »

pro_zac wrote: post #139
IncRnd wrote: post #126

This article was a fun read, and it really highlights how we trust the words on the tin to be accurate and not mistaken marketing gibberish. However, the part about the cost ranging from $40 - $80 is simply not true. I know this, because I purchased for $20 yesterday a faraday box to hold my auto key fobs and my cell phone. [1] There are very many items for sale at this price point, fabric, pouches and boxes. [1] htt…

Key fobs! Isn't there a scheme where thieves clone the signal from a key fob when the owner is asleep in their home and drive off with their car?

The attack involves relaying the signal next to the car. Essentially mimicking the key fob being close to the car.

For what I know you can not clone the key, nor can you record the signal and replay it whenever you want access. It's a one time thing to drive away to your nearest chop-shop/hideout.

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