Tin Foil Passports?

Daedala writes "The debate over contactless chips with biometric information in passports continues. Vendors have been chosen for testing in the U.S. and Australia. Privacy advocates are still arguing about the measure, as are security reporters and bloggers. The specs themselves are interesting, to say the least. The EETimes says that in interoperability tests, the potential chips could be read from 30 feet away. However, both they and the New York Times have published articles reporting vendors' low-cost solution: '[I]incorporate a layer of metal foil into the cover of the passport so it could be read only when opened.' Don't they know that the whole tinfoil hat thing is supposed to be a joke?"

Comments

Not actually based on a joke.

[paganizer]

A charged layer of tin foil will block most electromagnet signals, AKA Farrady cage.
a simple layer just won't cut it, though.

Re:Not actually based on a joke.

[dougmc]

Better still, save the metallized ziplock bag that your video card probably came in, and use it. Dual purpose -- keep RFI out, as well as moisture.

The anti-static bags that computer cards come in do very little to stop RF. Doubt this? Put your cell phone in one, then call yourself. It'll work fine. Tin foil will work *much* better, and no, it doesn't need to be grounded. (In fact, grounding will have no effect.) Again, this is very easy to test -- just wrap your cell phone (or any other radio) in tin foil -- it will not work.

Anti-static bags have high resistances. They're not completely insulators, but not good conductors either, and a Faraday cage needs a good conductor. Their high resistances allow static electricity (with many thousands of volts) to drain off, slowly. Tin foil *can* be used instead of an anti-static bag, but 1) if your circuit has potential somewhere (like a battery, or a charged capacitator) the tin foil will basically short circuit this, which is bad, and 2) it tends to look like a wad of tin foil, which may get thrown away as trash :)

I don't think that you would actually need to drag a chain behind you to stay at earth ground -- that's what the Faraday cage does.

A Faraday cage really has nothing to do with Earth ground. It certainly does not have to stay at the same potential as the Earth unless it's somehow connected to the Earth, and it'll equally as well connected or not connected to the Earth.

Old fashioned Faraday cages did have problems -- they generally use a wire mesh of some particular size, which doesn't stop ALL RF signals.

There's nothing `old fashioned' about any of this -- the first Faraday cage was built in 1836, and once the radio was invented, it was learned not long after that a Faraday cage will block any RF who's wavelength is much larger than the gaps in the cage. I'll bet this was known (and probably understood) long before 1930 or so. People use Faraday cages with a wire mesh today because it does what they need it to do. To do more would cost and weigh more, and might cause other problems (like not let air in, etc.) -- it's as simple as that.

Faraday cages block *electrostic* fields, and you really don't need a tight mesh at all for this. Even your car makes a reasonable Faraday cage. Blocking RF is an added bonus, but for that, you need to make sure the mesh is a good deal smaller than the wavelength of what you need to block.

So, if you need absolute protection against all frequencies of electromagnetic radiation, then you use something with no holes at all. If you also want to block magnetic fields (as the government will want to do to completely prevent TEMPEST attacks and such), then you'll make it out of something magnetic (mu-metal is ideal) and thick. And heavy, and expensive. But secure.