Testing Phone-Sized Faraday Bags
mattblaze.org
mattblaze.org
For a network switch, there are free and open source tools like iPerf to test and verify speeds are as advertised. For a faraday box, you have to go through all these steps (and knowledge learned) just to be able to test these. What about for vitamins, or pet food, or any other “durable” products that are supposed to last for X years?
In an age of snake oil salesmen, paid for reviewers, and fraudulent products on Amazon, there is a real opportunity for creating systems that enable individuals to verify products do what the sellers claim they do.
I buy online, I can return within two weeks no question asked.
It breaks within two years - I return it. Either I get a repaired one or a new one or my money back.
There are few exceptions but mostly it makes shopping quite secure.
Yes. There are bad actors. Yes people get ripped off by shady online stores. But if using trusted shop, PayPal or one of the known big shopping brands the experience is mostly good.
In the UK we have a warranty period with no particular limit, undergirded by the EU 2 year default, through the Consumer Rights Act -- basically it's founded on how long products would be reasonably expected to last, a fridge should last a decade, a cheap toy arguably far less.
But, I've had a problem with this that I think it's a useful example: Steam sold me a defective game, I tried to play it but the bugs ultimately made it impossible to enjoy (the purpose of entertainment!). Under the CRA digital goods are explicitly included in the ability to return when defective; but Steam/Valve decided their rules on "play" time trumped UK law. PayPal provided a refund (tiny amount of money) in accordance with their terms, but now Steam have taken revenge (the employee time spent on the issue certainly cost more than the original purchase), threatening to close, and then simply limiting my account. That should be illegal IMO, but I don't know if it is. I'm not going to pursue them at this point.
Imagine if a fast-food outlet said "if you complain about your food we'll ban you from buying from us", that would have a perverse effect on consumers and reduce the ability to push back against instances of low quality food. Sure, you can boycott them but that seems worse for everyone.
TL;DR at least in the digital domain, even with strong consumer protections companies can work around the law.
Amazon reviews are completely worthless, but very few other platforms have anywhere close to the same number of reviews on them. Most platforms have no verification of purchase for reviews. It's hard to determine information like "does this device require a cloud login? for which functionality? are there ads?" that isn't explicitly supplied by the manufacturer (or hidden by them). Negative reviews about product breaking quickly aren't very useful because people whose products work for a long time leave reviews at a lower rate. Google is almost useless for finding out information like this because of how SEO-gamed everything is, and the ol' "site:reddit.com" trick will only work for a while longer until these fraudsters create enough fake reviews on Reddit that it also succumbs (which is already beginning).
(rant "...and this problem will likely won't be solved anytime soon, because consumers don't care about these things. That's the reason that we're in this situation - consumer apathy. When was the last time you heard a non-tech-savvy relative say something along the lines of "Wow, this phone didn't last very long. Is there a place where I can add that data point so that other people will be more informed before they purchase one?" Users don't care about performance, privacy, or durability - they just want to watch Netflix and pay the lowest sticker price they can (regardless of annual cost of ownership). You see people self-organizing around things like video games or paintball or book clubs or whatever all the time - why won't they put even a fraction of that effort into ensuring that they buy a good car?")
I think that's not the issue. Consumers DO care about durable products, and consumers DO share their experience. Consumers talk to others about stuff they like all the time, and they also complain to others when stuff doesn't work. Consumers also spend a lot of time online researching products.
Amazon Reviews were amazing in the beginning, because so many customers shared their honest experience.
The problem is that as soon as there is a popular place where people go to read reviews, companies realise they can make a lot of money if they post fraudulent reviews (or send free samples to folks who write positive reviews). Products with good reviews make lots of money, so companies are going to put a lot of effort into getting good reviews.
On the other hand, consumers trying to share their honest experience don't have anything to gain from doing so, so they are not going to put as much effort into sharing their experience.
Fuelling it is that there are people in the “I want my <$500 things to last a long time because they should last” and people in the “If there’s a QC issue or it’s not as advertised I’ll return it, and if it breaks after I use it for a while I’ll just get the then-current one which will be better anyways”, and almost no one in between.
In our current society people with funds and not time see a clear ROI for shooting for 80% success because it means not having to spend time thinking or sorting out logistics.
Some people, when confronted with a problem, think "I know, I'll use regular expressions." Now they have two problems. - Jamie Zawinski via Coding Horror [0]
To your point, maybe Zawinski's aphorism is broader than regexp.
The quote investigation [1] linked from CH is well worth reading.
0. https://blog.codinghorror.com/regular-expressions-now-you-ha...
We could, as a society, make rules that prohibit these things and create organizations with the expertise and power to enforce those rules. We are hardly helpless, but the political trend is to forgo and even decry that power, do nothing, and then whine about how helpless we are.
These agencies seem to test one vector while ignoring everything else. I don't trust them.
https://www.consumerreports.org/food-safety/your-herbs-and-s...
https://www.consumerlab.com/ does a great job testing vitamins and other various things put in or on your body. Well worth the subscription price.
tl;dw They're building a setup where they can test a bunch of computer equipment with standardised tests (built by them) in a standardised environment (also built by themselves).
It’s more a misplaced disappointment along the lines of “this is why we can’t have nice things” (because at a certain point money corrupts it). The number of times I’ve seen products and brands really have something special, and believe in them, and purchase and use the products, only to have them sacrifice integrity for money at some point is heartbreaking.
But that’s a me problem (and society’s problem), and not a Consumer Reports problem.
The post does mention something similar near the bottom where they suggest putting an AirTag in the bag and seeing if your phone can find it.
Drink shakers are cheap and widely available. The average hotel room in any medium/large hotel chain probably includes a shaker as a standard item as part of the minibar. The simple two-cup style (as seen in [1]) is preferred over the fancier "strainer top" style because you can press the two cups together; this should cause the inner cup to slightly cut into and/or deform the outer cup along the circle where they join together. The seal between the cups should work sort of like the knife-edge seals used in vacuum chambers.
A metal box or conductive bag is only a Faraday cage if it is fully closed/sealed. Any imperfection in the seal or hole[2] might allow the radio signal to leak out. Most improvised items (freezer, random metal box, etc) have poor seals. Making a high quality cage that actually block a modern phone can be done without much trouble, but the drink shaker method is the only method I know of that will do the job using widely available (free) or very cheap ($10-ish?) parts.
[1] https://ae01.alicdn.com/kf/HLB1yRyhXZTxK1Rjy0Fgq6yovpXaZ/Win...
[2] Holes of sufficient size. How big are the waves you are trying to block?
Maybe the hotels you stay in, Bond, James Bond.
[1] If you registered for FanimeCon 2000-2011, the weird software you had to use was my fault...
I've stayed in dozens of hotels all over the world, and never once have I seen a cocktail shaker in the minibar?!
And I don't recall ever finding one of these things in a hotel room, even in Europe.
Ref skin depth of different materials at different EM frequencies:https://upload.wikimedia.org/wikipedia/commons/f/f3/Skin_dep...
Dad: What's five plus five?
yosito: Ten!
D: How many fingers do you have?
y: Ten!
D: What's an aluminum can made out of?
y: Tin!
D: Wrong! Aluminum!
“Security Mints - sweet & secure”.
Maybe a kickstarter?
To answer [2] How big are the waves you're trying to block? - it's actually crack length not width that usually determines the effective re-radiating antenna length. They can be very narrow, but a long (a few cm) crack will allow one polarization through almost completely.
I've run this test with a GSM base station and confirmed the effectiveness. If you want to test communication with a device to a base station, but have many other local antennas interfering and want to fit many devices inside... it's a decent choice. The alternatives are less convenient and usually thousands of dollars to construct.
The reason for the tuned slots is that it's basically impossible to make a conventional metal joint which will seal sufficiently well.
I've also worked in RF Antenna test rooms with seals that are expensive, finicky, and easy to damage... they're also at least $10k and usually much much more. In a corporate environment that's not a problem, but for a home lab it's unrealistic.
If these bags were big enough to put a few phones and a small base antenna in they'd have other uses.
Difference 1 is the wavelength. Light has a wavelengths of 400-700nm, whereas radio waves used by phones have wavelengths in the mm and cm range.
If structures are of similar size to the wavelength, then waves can "bend around" obstacles. This effect is called diffraction and can be observed with sound waves, electromagnetic waves, water waves, etc.
Difference 2 is the photon energy / frequency. How well radiation is absorbed depends on the photon energy. There are lots of molecules that absorb visible light very well, so it's easy to make surfaces that absorb light. But there are few things that absorb radio waves as well, so it's hard to make things that neither reflect nor transmit radio waves.
I remember going caving and we would have to go 100m or more through many different turns before we all turned our lamps off and truly experienced perfect dark.
A hole/leak in the metal wall of a Faraday cage is going to be a lot more reflective and can easily act like a crude waveguide[1].
[1] https://en.wikipedia.org/wiki/Waveguide_%28radio_frequency%2...
Our eyes simply aren't very sensitive instruments. And the visible part of the spectrum is uncharacteristically full of 'noise', so it makes some sense that our eyes don't need to detect any signals that are too far below the noise-floor.
That makes me wonder. How much 'darker' is any given bit of radio spectrum as compared to the visual spectrum earth at night.
I take umbrage with that statement! Our eyes are exquisitely sensitive, and most importantly, have staggering dynamic range.
Our eyes are capable of perceiving a single photon [1], albeit noisily (I've been lucky enough to have performed this experiment myself!).
But the greatest thing about our eyes is the dynamic range: the difference in brightness between a moonless, starry night (which we are perfectly capable of navigating by eyesight) and a bright sunny day is nine orders of magnitude. A bright day is a billion times brighter!
Show me an RF receiver or light camera with that dynamic range!
The one place our eyes are limited is in frequency range.
The magnitude of the dynamic range is even more impressive if converted to 'stops' from photography, yielding about 30 stops (1 stop halves the light). Whereas a really good camera will do about 15 stops. Though I suppose that the camera gets 15 stops in a single 'scene'. Whilst the 30 stop figure for the human eye does not hold up if half your vision is taken up by daylight and the other half by a night sky. For a single 'scene' I think it becomes hard to define the dynamic range of a human eye though.
If the signal gets choppy and you miss some of it, how do you know what you missed?
`..--- -.... ----- -----` (2600) could come through as `..- -. —` (Uno). Uno is a valid word, so passes validation, but it’s the wrong message.
What Reed-Solomon allows us to do is pad the message with n% of error correcting ‘bits’. That way, if >100-n% of the message gets through, the whole message can be reconstructed from whatever bits that made it. And if not enough of the message made it, it immediately fails the validation check and so you know you must resend the message.
It’s so handy and so solid that it’s used almost everywhere. From optical discs to ECC ram to radio communications and a bunch more.
There is:
- lines-of-sight propagation in free space,
- reflect from the surfaces like light (spectacular reflection)
- microwaves can be channeled trough tubes (think sound waves). If you fold a conductive material like tin foil multiple times, it can still work as a wave guide and escape.
So I mainly used the room because that's where the magic blanket was - which was easier to use than ensuring the room was set up correctly.
Back in the day working for Symbian I used to regularly have to run a load of automated Bluetooth tests. Unfortunately there were 200+ engineers in the close vicinity of my test setup and they all had smartphones and all had Bluetooth turned on, causing loads of the test to timeout. We were very pleased with ourselves when we thought of using a biscuit tin as a Faraday cage to try and improve things. Didn't work as well as we hoped, but got the tests running within their timeouts. I always thought it'd be interesting to try using an old microwave.
Best thing was that we got to eat all the biscuits first :)
Square tin can works better because those seem to usually scratch on the corners. The smallest square tin can you can find should work best. A tin can sealed with adhesive cooper tape should work pretty well even if the copper tape is isolated by the paint on the can.
Edit: clarification.
It works for me with a cookie tin, the phone is wrapped in a towel.
A faraday cage/bag does not protect x-ray since it ‘only’ blocks electromagnetic fields.
So I guess in the case you mention it’s more hiding in the insulation/empty space of an appliance.
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.
After searching, I found that Kaspersky has a blog post on the topic: https://usa.kaspersky.com/blog/terminator-dark-fate-chips/18...
It surprised me that chip bags were more effective in their test than cookie tins, but only when they double-bagged it
https://arstechnica.com/information-technology/2017/11/austr...
I've had a lot of fun in the past trying to shield Bluetooth devices for testing... metal filing cabinet? Practically no attenuation. Biscuit tin? Minimal attenuation like in the article.
Modern radio receivers are ridiculously sensitive.
> "Makeshift Pouch 1: Electrostatic Mylar Bag"
This is not a mylar bag. It's frustrating how often these two are confused, especially when said confusion can result in component damage.
On the other hand, aluminium foil is incredibly commonly available, if not in a kitchen draw, it will be at the nearest shop. Although unreliable, the _potentially_ high attenuation the author shared is pretty good (we don't know his worst reading), better than all other improvised solutions tested, and similar to commercial products. I wonder if a more reliable construction method could be found.
I'm not sure what movie scene scenario I'm envisioning, but in the case you needed a Faraday cage and don't constantly carry one around, perhaps simply taking an entire kitchen roll of foil and wrapping the device into a giant unsightly ball of it would be a reliable enough process for an "emergency" (if not pocket sized). i.e rather than trying to make a neatly folded minimal version, just resort to sheer number of layers of material - unless RF doesn't care and even 1000 layers with tiny gaps is no good?
[edit] Similarly, I wonder how well (or poorly) common household appliances work as a Faraday cage, e.g a fridge, microwave-oven - From what the author described, it seems they would all have too many gaps, however they are also constructed from higher gauge metals... i'm particularly interested in a microwave-oven which is specifically designed to reflect and retain microwave frequency fields.
You can test this: put your phone in the microwave and try to call it. Over the years I have had about a 75% success rate.
Other household appliances tend to be even worse; any gaps in metallic seals effectively turn into slot antennas and let signals through. You need a conductive mesh gasket to stop this, and I generally don't see mesh gaskets on consumer appliances.
Your "make an al-foil ball" strategy is what I would resort to in a pinch (I have some nice Anritsu shield boxes, but those are cheating). Quantity is a quality of its own. My only addition would be making sure that the gaps tend to not line up. You want to make it difficult for the "slot antennas" modeling the gaps in each layer to couple to each other.
DO NOT MICROWAVE YOUR PHONE.
The test involves placing your phone in the microwave and closing the door without turning the microwave on. I'd unplug the microwave before trying this.
— https://www.reddit.com/r/tumblr/comments/jy8wzj/rinse_your_e...
Also, remember to ground your faraday cages.
Why?
https://www.mikeholt.com/technical-stray-voltage-newsletter-...
In particular, foil is cheap, so rolling up in several layers (3? 5? 10?) and twisting the ends cracker-style ought to be more reliable and practical than trying to do it with one layer and fiddly seams. A suggested minimum number of layers and number of twists would be useful.
I also read an article this year by a guy that made his house radio-wave proof, because, he claimed, he was very sensitive to radio waves. It was WAY more involved than I would have guessed - for the same reasons discussed in this article and in this HN discussion. Nails and screws are a problem. Windows are a big problem. But still - how cool to be cut off from the onslaught of EM radiation.
Perhaps it sounds like overkill, but it’s the only way I seem to be able to fully isolate the devices.
That said, I’d probably just buy a bag... but I’ve been trying to keep it with what I have lying around the house.
That means at the junction between the tin and the lid (and maybe other joins), there isn't an electrical connection all along.
Having two metal surfaces next to eachother, but with an insulator in between, acts like a 'choke flange'[1]. However, they only work at one specific frequency - at all other frequencies they will leak either a little signal or a lot/all the signal.
The same technique is used on a microwave door edge to keep the microwaves in. It's why keeping the microwave door edge clean is critical to safety - a small bit of food there isn't an insulator like the paint, and energy leaks out.
[1]: https://en.wikipedia.org/wiki/Waveguide_flange#Choke_connect...
I do miss the old days of tuning the rabbit ears on top of the tv for best reception.
Did you get an earworm? I sure did.
Wikipedia also states they are more effective at blocking incoming than outgoing signals. Can anyone clarify the situation?
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).
I do not understand your question, otherwise.
(Not a criticism, just an interested comment which may be very wrong though).
This is a mental operation, not physically possible. The difference is real: for example, charge inside a perfect conductor cavity generates electrostatic field outside. A charge outside perfect conductor cavity does not generate any static field inside.
But would a point charge outside a conductor cavity ever come to equilibrium where it does generate an electric field inside the conductor cavity? Assuming compact but very large universe. It seems strange but I guess it would.
Thank you for this comment, truly enlightening (I am a mathematician and know 0 physics). Shall have to think about it.
https://www.androidpolice.com/2020/08/22/this-smartphone-has...
Or at least phone with a removable battery
I know I will never buy a phone without a 3.5 audio jack
Non-removable batteries is the new standard because of that. (Also stream lining) Which is bad for security (the point of the article)
I don't use bluetooth because it is not reliable enough for me, because I don't like charging another device and, less importantly, because in the past it has been exploited to hack devices. The audio jack is the one port I prefer never to part with.
Depending on your occupation it can have very serious consequences.
Red plastic == electrostatic dissipative. It is not good at conducting electricity -- it is still very good insulator. It just has ability to dissipate electric charge fast enough so that it will not accumulate in normal use.
What you have wanted to check is a clear bag with metalized layer (which is silver or gray looking). It should, per my understanding, act as much better faraday cage than an electrostatic dissipative bag. And I would be really interested in seeing that measurement.
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.
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.
Even if the radio is blocked, how does that stop a device from collecting data anyway, and exfiltrating it the moment it finds a network? Won't it look for a network the moment you take it out of the bag? And don't you have to remove it from the bag to use it practically?
Ultimately, if your device is compromised or untrustworthy to the extent that it has to be policed this way, is it not safer to just... get rid of it?
I made a pouch for my car's key fob with aluminum foil and metal tape. It isn't as pretty as the ones you can buy, but it wasn't $25 either and It has worked really well.
https://www.reddit.com/r/whatisthisthing/comments/r7kb03/my_...
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.
I placed my phone wrapped in a towel inside a metal box: as soon as I close the lid I can't ping the phone on local WiFi and can't reach it with call (it goes direct to voicemail as if the phone was switched off). The GPS doesn't record any position while in the box. I didn't test the Bluetooth though.
Same thing for my car keys inside a paper towel and aluminum foil: impossible to open the car even at touching distance.
I wonder if he wrapped the device before putting it in the box or aluminum.
https://letsfixstuff.org/2021/04/modem-chips-embedded-in-vot...
http://web.archive.org/web/20100708230258/http://people.csai...
But how come these are all US-exclusive. It seems both winners don't ship to EU :/
Per-se, yes, agreed, but I was wondering whether the transmitter and receiver antenna couple into the surrounding screen differently. The degree of coupling may de-tune them differently. If so then the setup which most accurately represents the intended use would be with the receiver inside the screen.
Idle comment: we use their smaller keychain bags for car fobs, after hearing with dismay first- and second- hand accounts of relay attacks being used to steal or ransack cars in our neighborhood (94110). We now keep our fobs in them except in use.
All in all, if you NEED something like this, your opec had better include more than this.
Why have the phone if it's not connected to the network? It's a communication device. Just leave the phone home.
I always thought it was 10dB, or one B that was a change of factor 10. Have I missed something?
Power is proportional to voltage squared.
So a 10x increase in voltage == a 10^2 = 100x increase in power == a 20dB increase in power.
I tested some by putting the phone in the Faraday container, and then calling its number to see if it rang.
[0] https://wiki.pine64.org/index.php/PinePhone#PinePhone_board_...
[1] https://source.puri.sm/Librem5/community-wiki/-/wikis/Freque...
Not really, tinfoil actually worked, but it was apparently too difficult to get right:
> In my experiments, I found I could sometimes achieve approximately 90 dB attenuation by carefully wrapping the generator in foil and double folding the seams on all sides, which is quite good (comparable to commercial pouches).
This actually matches my experience with a GPS logger. It only had an on/off switch and I wanted to download the track from my trip without getting points from the download location at the end. IIRC, it was still able to get fixes even wrapped in tin foil.
Eventually it will radiate the same amount of energy as the transmitter inside it, but in infrared wavelengths and without whatever modulation was carrying the signal.
does not
I've made a few DIY Faraday bags that way. They're not perfect of course, but less expensive than these bags most of the time.
Edit: Ah, I see this was covered in the article. I didn't read it before posting this comment.
A good portion of phones, on the other hand, do seem to be made of the fruit of the domesticated Malus.