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RF shielding

Discussion of forensic issues related to all types of mobile phones and underlying technologies (GSM, GPRS, UMTS/3G, HSDPA, LTE, Bluetooth etc.)
Subforums: Mobile Telephone Case Law
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Re: RF shielding

Post Posted: Mon Jan 28, 2013 9:48 am

- Bulldawg

I have this bag, and I have a warning. In an area of particularly strong signal, I've had a phone in this bag connect to the tower and download a couple SMS messages. I don't know if this would happen with any other bag--I suspect it would--so it's best to just use the bag long enough to put the device in airplane mode.

Just for the record:

www.forensicfocus.com/...1/#6562541

In the comparative tests made by Purdue University
docs.lib.purdue.edu/cg...ei-redir=1
that particular make/model didn't do very well:
In this graph it is clear to see that the Black Hole Bag fails to isolate most of the
mobile phones during the tests. It is evident that SMS messages are the least isolated of
the call types. Voice calls started out penetrating this shield as often as SMS but were
more affected by time. This is most likely explained by the increase in noise in the
communication channel that being placed inside the RF shield causes. As the SNR
decreases the phones have a harder time communicating with the tower despite still
receiving some signal. This supports the hypothesis that SMS messages require less SNR
than the other call types.
Overall the Black Hole Bag had a 54.12% failure rate during these tests.

while still better than others, the really preoccupying issue coming from the conclusions is that no "safe" product was found:
It is evident that the shields do not always isolate the mobile phones. None of the
RF shields tested were able to successfully isolate the phones 100% of the time.


jaclaz
_________________
- In theory there is no difference between theory and practice, but in practice there is. - 

jaclaz
Senior Member
 
 
  

Re: RF shielding

Post Posted: Mon Jan 28, 2013 2:28 pm

Hi Jaclaz,

Thanks for the info here and reference to the study. This test was done by Eric Katz, a graduate student at Purdue, in 2010 with an earlier version of our Black Hole Standard Faraday Bag. I know it's a little confusing but the brand is "Black Hole" and we currently have 7 different types. The Black Hole Data Bag is not the same one in the test, it wasn't out at that time. The bag in the test has similar shielding to the rest (all of the bags experienced failures in certain situations), but it was an earlier version, of which we have upgraded the shielding since.

All of the bags are independently tested. In general, the non-window bags shield about 15-30% more effectively than the window bags, due to the material. We do point this out on our site so users are aware of the differences between the bags. Black Hole Bags Testing That's why placing the Data Bag in the the separate faraday Transport Bag (non-window bag), is the only way to ensure the highest level of shielding in unknown signal environments. Essentially the process is to place the device in the Data Bag and connect to the shielded USB block, then attach a battery externally to keep it live. When the device is back in your known environment, where you know you're not sitting under a tower, you remove the bag and connect to a computer or analysis tool such as XRY. It's the added protection that's needed to shield in the field.

In general we know that faraday bags are not an on/off solution. They are designed to attenuate a signal to a point of disconnecting from a network, but sometimes they will fail if the signal is too strong. A typical failure situation might be when we are very close to a tower with a high signal strength device. If the user is worried about this type of scenario, the best solution is to place a window bag inside of a non-window bag. Our Black Hole Xlarge Non-window Bag is great for placing multiple smaller bags into during field transport. The benefits of using a faraday bag do outweigh the drawbacks, as user error and attenuation strength can cause far more failures than the bag itself. Paint cans and tin foil might work, but leaving the effectiveness of this solution up to the attentiveness and training of the person who seizes it is not a good idea.  

rjudy55
Member
 
 
  

Re: RF shielding

Post Posted: Mon Jan 28, 2013 2:38 pm

Thanks for the info, jaclaz. I wouldn't say I've had anywhere near a 50% failure rate with my version of the Black Hole bag. A couple SMS messages on an HTC Thunderbolt are all I've seen. My personal BlackBerry and several iPhone (3GS, 4S and 5) have all been properly shielded by this bag. I'm less than a block from a tower too, so it's a pretty strong signal area.

If possible, get the phones delivered to you in airplane mode. Since I deal with civil cases, this is usually possible.  

Bulldawg
Senior Member
 
 
  

Re: RF shielding

Post Posted: Mon Jan 28, 2013 3:39 pm

- Bulldawg
Thanks for the info, jaclaz. I wouldn't say I've had anywhere near a 50% failure rate with my version of the Black Hole bag. A couple SMS messages on an HTC Thunderbolt are all I've seen. My personal BlackBerry and several iPhone (3GS, 4S and 5) have all been properly shielded by this bag. I'm less than a block from a tower too, so it's a pretty strong signal area.

If possible, get the phones delivered to you in airplane mode. Since I deal with civil cases, this is usually possible.

Sure, but during the cited test the handies in the bags were "bombarded" by a heavy load of data on purpose, SMS, MMS and voice calls, and they compared what was sent to what was received.
If in your real life experience 4 SMS were sent and 2 were received by the Thunderbolt thingy inside the bag, the bag failed for a similar 50%, but if in total two SMS were sent and you received both of them it failed 100%, but if 8 SMS were sent and only two were received you have a much lower rate....

@rjudy55
I am pretty sure you try your best to have your bags shielding effectively Smile and I am perfectly confident that the testing you make are as accurate as possible and that your products (newer models) offer added/better shielding capabilities.

One of the points raised by Eric Katz still remains, however.

I perfectly understand how your testing methodology is correct and possibly a much more scientific one (at theoretical level), the approach by Mr. Katz however highlighted how in practical tests - at least for the hardware tested at the time - the sheer data expressed in db (signal attenuation) was not

From the docs on your page (first two items, one with window and one without) the signal attenuation is typically 44-50 db for the "windowed" and 54-60 db for the non-window.

This measures - accurate as they might be - give values that are "meaningless" (please bear with me) from a practical stand point.

As we don't have (and the mentioned thesis only partially answers this) properly terms of comparison, if you prefer we miss some "fuzzy" data.

If you have to describe the distance to (say) a nearby shop, and you are used to Imperial, you would say "Round the corner, no more than 100 yards", another "you" but used to metrical system would probably say "Round the corner, about 100 metres".
Scientifically the two measures are described with an approximation of almost 10 % but the person to which you are giving the information will have anyway a "good enough" kind of info.

What I guess would be useful would be more "real world references", even if less accurate, like "can shield a phone up to (say) 200 meters (or yards) from a tower/antenna".

The procedure of wrapping the (windowed) bag inside another (non-windowed) bag (or other heavily shielded conductor) makes of course a lot of sense, and in theory should also be the recommended procedure, expecially in countries where cellular technology/coverage is exapnding and - even if "yesterday" nothing happened "today" some telephone company has placed a new (or replaced an old one with a much more powerful) apparatus.

This (the measurement of the combined effect of the two bags in terms of signal attenuation) could be in any case a nice added set of data to your documents.

As a subject for research it could be also intersting to evaluate the effectiveness of further layers (such as putting the two bags, one into another into a tin can for added shielding).

As I see it being able to reach 100% (or as nearly as possible to 100%) certainty that during transport and until the "package" is opened in a controlled environment no signals reach the seized device - while being probably overkill in practice (you need to meet two conditions concurrently, being extremely near to a powerful tower AND have something, SMS, MMS, voice sent to the handy in the limited time you are under this "restricted" area of possible influence) might help in having quite a few of the professionals involved sleep better at night.

jaclaz
_________________
- In theory there is no difference between theory and practice, but in practice there is. - 

jaclaz
Senior Member
 
 
  

Re: RF shielding

Post Posted: Mon Jan 28, 2013 5:54 pm

- jaclaz
- Bulldawg
Thanks for the info, jaclaz. I wouldn't say I've had anywhere near a 50% failure rate with my version of the Black Hole bag. A couple SMS messages on an HTC Thunderbolt are all I've seen. My personal BlackBerry and several iPhone (3GS, 4S and 5) have all been properly shielded by this bag. I'm less than a block from a tower too, so it's a pretty strong signal area.

If possible, get the phones delivered to you in airplane mode. Since I deal with civil cases, this is usually possible.

Sure, but during the cited test the handies in the bags were "bombarded" by a heavy load of data on purpose, SMS, MMS and voice calls, and they compared what was sent to what was received.
If in your real life experience 4 SMS were sent and 2 were received by the Thunderbolt thingy inside the bag, the bag failed for a similar 50%, but if in total two SMS were sent and you received both of them it failed 100%, but if 8 SMS were sent and only two were received you have a much lower rate....

@rjudy55
I am pretty sure you try your best to have your bags shielding effectively Smile and I am perfectly confident that the testing you make are as accurate as possible and that your products (newer models) offer added/better shielding capabilities.

One of the points raised by Eric Katz still remains, however.

I perfectly understand how your testing methodology is correct and possibly a much more scientific one (at theoretical level), the approach by Mr. Katz however highlighted how in practical tests - at least for the hardware tested at the time - the sheer data expressed in db (signal attenuation) was not

From the docs on your page (first two items, one with window and one without) the signal attenuation is typically 44-50 db for the "windowed" and 54-60 db for the non-window.

This measures - accurate as they might be - give values that are "meaningless" (please bear with me) from a practical stand point.

As we don't have (and the mentioned thesis only partially answers this) properly terms of comparison, if you prefer we miss some "fuzzy" data.

If you have to describe the distance to (say) a nearby shop, and you are used to Imperial, you would say "Round the corner, no more than 100 yards", another "you" but used to metrical system would probably say "Round the corner, about 100 metres".
Scientifically the two measures are described with an approximation of almost 10 % but the person to which you are giving the information will have anyway a "good enough" kind of info.

What I guess would be useful would be more "real world references", even if less accurate, like "can shield a phone up to (say) 200 meters (or yards) from a tower/antenna".

The procedure of wrapping the (windowed) bag inside another (non-windowed) bag (or other heavily shielded conductor) makes of course a lot of sense, and in theory should also be the recommended procedure, expecially in countries where cellular technology/coverage is exapnding and - even if "yesterday" nothing happened "today" some telephone company has placed a new (or replaced an old one with a much more powerful) apparatus.

This (the measurement of the combined effect of the two bags in terms of signal attenuation) could be in any case a nice added set of data to your documents.

As a subject for research it could be also intersting to evaluate the effectiveness of further layers (such as putting the two bags, one into another into a tin can for added shielding).

As I see it being able to reach 100% (or as nearly as possible to 100%) certainty that during transport and until the "package" is opened in a controlled environment no signals reach the seized device - while being probably overkill in practice (you need to meet two conditions concurrently, being extremely near to a powerful tower AND have something, SMS, MMS, voice sent to the handy in the limited time you are under this "restricted" area of possible influence) might help in having quite a few of the professionals involved sleep better at night.

jaclaz


Within the narrow corridor of probability testing where a device contained in a physical RF dampening field container that may be susceptible, as set out by jaclaz, here are some images at the weblinks below that may assist in providing a visual idea of RF areas and the considered 'dwell time' conditions the container may be exposed to RF conditions when:

- static
- slow traverse
- speed

(The research tests may equally consider the robustness/distortion of the container material with respect to being moved around under different conditions during transportation.)

trewmte.blogspot.co.uk...art-2.html

Also the density of masts/towers in an area and the transmission technology/ies that may be relevant:

trewmte.blogspot.co.uk...tion.html.

Lastly, in-building solutions (IBS) have significantly increased and improved, so perhaps a police building or police office in a city building that once previously had poor coverage (externally) may have had an IBS installed (which is another point I believe jaclaz also makes with respect to 'changes').
_________________
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Mobile Telephone Examination Board (MTEB) - LinkedIn
Mobile Telephone Evidence & Forensics trewmte.blogspot.com
ForensicMobex now MTEB Linkedin Subgroup 

trewmte
Senior Member
 
 
  

Re: RF shielding

Post Posted: Mon Jan 28, 2013 7:02 pm

Jaclaz - Good points. And yes, this stuff can seem arbitrary until put into practice. Here's a nice breakdown with some indicators of signal to db. http://powerfulsignal.com/cell-signal-strength.aspx. And you're right, we should post more of the "practical application" type stuff on our site to help our users understand what they're dealing with. Putting your phone into field mode always helps as well.

TrewMTE - Thanks for the CSA breakdown, running through it now.

Cheers,
Ryan  

rjudy55
Member
 
 
  

Re: RF shielding

Post Posted: Mon Jan 28, 2013 8:03 pm

- taurean25
All,

Does anyone know of any RF shielding solutions that provide battery power to keep the acquired mobile device powered?

There maybe situations where if the device looses power, it may not be possible to gain access to the device again due to encryption or difficult passcodes.


The cellphone battery lose energy very quickly when RF shielding,because searching signal never stop.so u can use the Shielding bag with the external battery by USB port:)  

Horking
Member
 
 
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