Revision as of 17:44, 1 February 2017

The electromagnetic spectrum

The electromagnetic spectrum or electric radio spectrum is not something material, but the space that is in the air that goes from the ground to the highest part of the sky. In this space, bands frequencies through which airplanes, wi-fi, bluetooth, walkie talkies, radios, telephones communicate are organized. The fact that our phones can be 2G, 3G, 4G means that they are using different bands of the electromagnetic space, through which the information circulates.

For more information about the electromagnetic space: https://imagine.gsfc.nasa.gov/science/toolbox/emspectrum1.html https://en.wikipedia.org/wiki/Electromagnetic_spectrum

Faraday Cage

It is known as a cage or box of Faraday the effect by which the electromagnetic field inside a conductor in equilibrium is null, nullifying the effect of the external fields. This is because, when the conductor is subjected to an external electromagnetic field, it is polarized, so that it is positively charged in the direction of the electromagnetic field, and negatively charged in the opposite direction. Since the conductor has been polarized, it generates an electric field equal in magnitude but opposite in the direction of the electromagnetic field, then the sum of both fields inside the conductor will be equal to 0.

It is evident in many everyday situations, for example, the malfunction of mobile phones inside elevators or buildings with steel grid structure. One way to check this is with a radio tuned to a Middle Wave station. When it is surrounded with a newspaper, the sound is heard correctly, but if we replace the paper with aluminum foil, the radio will cease to emit sounds: aluminum is an electric conductor and causes Faraday's cage effect.

This phenomenon, discovered by Michael Faraday in 1836, has an important application in airplanes or in the protection of sensitive electronic equipment, such as hard disks or radio and television repeaters located on mountain peaks and exposed to electromagnetic disturbances caused by storms . It also currently serves to block the reading of RFID (Radio Frequency Identifiers) chips, which store personal information that can be intercepted by anyone with a radio-frequency scanner. These chips are found in objects such as passports, credit cards and some driver's licenses.

The Faraday box allows to block the communication of a device with the outside. In the case of mobile phones, they emit signals constantly, even when they are switched off. GPS, which allows us to locate where we are, no matter if it is off or on, also the phone will be locateable by towers that triangulate the signals. The fact that your phone has no signal (when you can not call), does not imply that you are not locateable, or that you have stopped sending signals.

Some household appliances work as Faraday boxes, for example the freezer in the refrigerator, as having a thick layer of metal can have the same effect, if we introduce the cell phone inside, we prevent signals from being emitted.

About Faraday cage: https://en.wikipedia.org/wiki/Faraday_cage

Experiment of creating a Farady cage: https://backyardbrains.com/experiments/faraday

How they can intercept the information on your phone

One way to intercept the information on your phone is through an IMSI-catcher, a device that can be installed anywhere (a car, a house nearby, etc.), and which simulates to be the antenna of a telephone operator mobile. When installed, the cell phones of this operator will automatically connect with this fake antenna. Thus, this device locates and identifies the switched phones that are in the sector, even if they are not communicating, registering and sending information that identifies them (such as telephone number and device number).

The IMSI-catcher can also relay the communications out of a particular cell phone in such a way that it can not perceive its presence. This way you can have direct access to the content of these broadcast communications that relays and can serve as a live listening device.

You can read a HowTo on IMSI-catcher: https://gendersec.tacticaltech.org/wiki/index.php/Detect_false_mobile_antennas

Fabricar una funda de Faraday

Hay varias formas de fabricar una bolsa para nuestros dispositivos móviles o tablets con el objetivo de que no sean rastreables y no emitan señales a través de las que nos puedan identificar o espiar.

Hay que conseguir primero que nada la tela conductora. Esta tela la puedes comprar por internet en sitios como estos:

ejemplo 1

Lo más importante es que cuando hagas la funda no quede ningún espacio abierto por donde se pueda fugar la señal. Fíjate bien de coser todos los bordes, puedes doblar la tela antes de coserla.

La funda se puede hacer con una máquina de coser o a mano. Puedes diseñar una forma de cerrarla, con un botón, con velcro, o simplemente con una pinza.

Si la tela no es muy gruesa ni potente, puedes usarla doble. También puedes, si deseas incrementar la estética de tu funda, usar otra tela para el recubrimiento exterior. Puedes probar distintos diseños y formas, como indica el dibujo:

Medidas de seguridad complementarias a la funda

Usar en grupo la funda puede ser una técnica bastante sospechosa si, por ejemplo, varios móviles vigilados, situados en una misma zona, se apagan o dejan de conectarse a la red al mismo momento. Si se hace de esta forma hará evidente que estas personas tienen algo que esconder o están en algo raro. En ese sentido la práctica más segura sigue siendo dejar tu teléfono en la casa, o al menos, sacarle la batería o meterlo en la funda antes de salir de tu casa para no revelar el lugar de encuentro.

Mucho cuidado ya que la bolsa de Faraday no anula el micrófono. Si bien el teléfono queda incomunicado con el exterior, podría habérselo instalado alguna herramienta que permita grabar para luego enviar dicha grabación. Asegúrate de mantener el teléfono en un lugar aislado acústicamente. Puedes poner el teléfono con su funda dentro de un frasco de vidrio hermético, en el refrigerador, o en otra habitación.

Links de interés

http://killyourphone.com/es/

http://briangreen.net/2010/11/diy-ultralight-faraday-cage-pouch.html

http://www.datenform.de/silvereng.html

http://makezine.com/2010/11/18/phonekerchief-blocks-cell-signals/

http://www.backdoorsurvival.com/how-to-build-a-simple-faraday-cage-for-emp-survival/

Tests a jaulas y fundas de Faraday (foros):

http://www.survivalistboards.com/showthread.php?t=156111 http://www.survivalistboards.com/showthread.php?t=231373 http://www.survivalistboards.com/showthread.php?t=301999