It's called an active emanation attack. Passive attacks interpret the electromagnetic signals that electronic devices naturally emanate. They try to reconstruct what the original information was. The active attacks work by doing the equivalent how you see trees at night with a flashlight: they hit the target with a signal, it is affected by what's there, it bounces back, and you get a distorted version of whatever that was. EMSEC standards, esp TEMPEST shielding, were invented to mitigate as much of that as possible. Although it's classified, there's been a number of sites talking about public and some declassified info.
I don't have the link to old site everyone in hacking community used. Here's one provider that describes it nicely plus illustrates what the products look like. They used to be way bulkier.
Here's the quote that first taught me about the risk you described:
"A STU-III is a highly sophisticated digital device; however, they suffer from a particular nasty vulnerability to strong RF signals that if not properly addressed can cause the accidental disclosure of classified information, and recovery of the keys by an eavesdropper. While the unit itself is well shielded, the power line feeding the unit may not have a clean ground (thus negating the shielding)... The best way to deal with this is to never have a cellular telephone or pager on your person when using a STU, or within a radius of at least thirty feet (in any direction) from an operational STU (even with a good ground). If the STU is being used in a SCIF or secure facility a cell phone is supposed to be an excluded item, but it is simply amazing how many government people (who know better) forget to turn off their phone before entering controlled areas and thus cause classified materials to be compromised."
These are also another piece of evidence for two claims I often make: mainstream security folks don't produce devices that are actually secure; NSA/DOD are opponents of securing American infrastructure. On the first, high-assurance security and NSA certifications for TS/SCI demanded EMSEC since they were known attacks, esp by US and Russia. Mainstream ignored them mostly for "secure" products with only a handful trying to do something.
The second claim is from fact that security agencies misled U.S. companies and individuals about these risks specifically so they could use the attacks on them if needed. Although I don't recall if current, they also refused to sell TEMPEST-certified systems outside Defense in the past. So, NSA and pals were known to keep us vulnerable on purpose long before Snowden leaks. I've been griping about and trying to raise awareness of it for some time. Examples:
I don't have the link to old site everyone in hacking community used. Here's one provider that describes it nicely plus illustrates what the products look like. They used to be way bulkier.
http://sst.ws/what-is-tempest.php
Some more links. Elovici's lab is at the forefront of new attacks.
http://www.elastic.org/~fche/mirrors/www.cryptome.org/nsa-te...
http://tempest-inc.com/
https://en.wikipedia.org/wiki/Yuval_Elovici
Here's the quote that first taught me about the risk you described:
"A STU-III is a highly sophisticated digital device; however, they suffer from a particular nasty vulnerability to strong RF signals that if not properly addressed can cause the accidental disclosure of classified information, and recovery of the keys by an eavesdropper. While the unit itself is well shielded, the power line feeding the unit may not have a clean ground (thus negating the shielding)... The best way to deal with this is to never have a cellular telephone or pager on your person when using a STU, or within a radius of at least thirty feet (in any direction) from an operational STU (even with a good ground). If the STU is being used in a SCIF or secure facility a cell phone is supposed to be an excluded item, but it is simply amazing how many government people (who know better) forget to turn off their phone before entering controlled areas and thus cause classified materials to be compromised."
These are also another piece of evidence for two claims I often make: mainstream security folks don't produce devices that are actually secure; NSA/DOD are opponents of securing American infrastructure. On the first, high-assurance security and NSA certifications for TS/SCI demanded EMSEC since they were known attacks, esp by US and Russia. Mainstream ignored them mostly for "secure" products with only a handful trying to do something.
The second claim is from fact that security agencies misled U.S. companies and individuals about these risks specifically so they could use the attacks on them if needed. Although I don't recall if current, they also refused to sell TEMPEST-certified systems outside Defense in the past. So, NSA and pals were known to keep us vulnerable on purpose long before Snowden leaks. I've been griping about and trying to raise awareness of it for some time. Examples:
https://www.schneier.com/blog/archives/2011/08/business_week...
https://www.schneier.com/blog/archives/2014/03/friday_squid_...