Schneier on Security

Clive Robinson • September 24, 2025 12:57 PM

@ Bruce, ALL,

Remember the “Greek Olympics” wiretapping of mobile phones probably by the NSA/CIA?

Well it appears that it’s happened again, this time a little more “home grown” with the assistance of the Israelis who are now on trial…

For “misdimenors”, under a very junior judge etc. And yes people are getting quite upset about the illegal activity of the time,

https://www.bbc.co.uk/news/articles/ced56p5l2wwo

Especially as those who were probably in cahoots if not incharge changed the law to make such spying legal…

So more fun and games.

Clive Robinson • September 25, 2025 3:31 AM

@ not important,

With regards “deliberate interference in the RF spectrum” or “intentional jamming” or the many other names people use. Different jurisdictions have different legislation, regulation, rules and much more.

However oddly perhaps the US bans the devices where ever they are used (including in laboratories).

Many other places do not care about use of jammers and for the good reason they are only interested in what it does to others. Thus what you do at home and stays in your home is between you and other people “who have a right” to be “on the property”. The same with mostly all other property.

That is the us “bans the equipment” other places “address the harms”. In the case of all radiated energy banning the “equipment” is actually a legal nightmare, where as “stopping the harms” is relatively easy legally.

Oh for those thinking that intentional jamming cell service via a CW or similar jammer is something that can be done over a wide area with GSM… that kind of ended when LTE became more common. And as 5G and 6G replace 4G and earlier it will be fairly pointless to try except over a very tiny area.

For those that want to know why it’s down to ‘Eb/N0’ or “energy per bit over noise density”

https://ensatellite.com/ebn0/

In the case of jamming the noise density is actually that from nature plus the jamming signal.

Now consider your jammer is a swept VCO unmodulated system. Your CW signal is narrow band which means at any point in time only a very very small part of the spectrum has energy from your jammer on it.

Low Probability of Intercept (LPI) modulation and modern data systems can be viewed as sending data in parallel across very wide bandwidths and with error correction.

Thus across very wide bandwidths you have to have more energy/Hz than the mobile phone handsets that in effect have all their energy in a very narrow frequency band that rapidly moves. Look up Spread Spectrum systems and jamming to see the problems involved.

Your only hope is high power close to the cell receiver…

Then there is the fact that GSM systems now use “phased array” antennas that can be thought of like telescopes that can point past an interference source by looking in it’s direction but in the direction of the handset signal.

Thus general unmodulated or CW jamming is not effective with newer data systems designed to deal with general interference.

So the only trick left is to occupy all the “baseband” channels… Which is a little difficult to explain these days.

So over simplistically, a cell site has a “backhaul” into the datacoms network backbone and has in theory a finite number of user connections at any given quality. Back in the days of ISDN and “circuit connect” this used fix amounts of data bandwidth regardless of actual data use. Well ISDN and similar are in effect gone, and many backhauls are “IP on Ethernet” or similar and are “packet switched” not “circuit switched”. This means more effective bandwidth utilisation by “average” not “peek”. To get around all users wanting peek use briefly quality is “degraded to fit”… This means that 100 no-voice calls take up about as much bandwidth as just a couple of voiced calls with peek use modulation.

To generate peak use voiced modulation continuously is actually quite hard. Thus your jammer would have an extraordinarily complicated modulation system that would require some “quite interesting” development work to put it politely.

Thus using a SIM-box that takes VoIP or other data source and sends it to the equivalent of 16 or more handsets can less expensively hardware wise jam just the same amount as 16 ordinary handsets with the same audio or data.

This is just one of the reasons the various defence planners around the world are closely looking at GSM systems to replace military radios for “Boots on the ground” as are Emergency Responder organisations.

Walkie Talkie “Private Mobile Radio”(PMR) is likewise undergoing significant change because it’s mostly a waste of spectrum resources by entities that really do not need them.

Part of this “transition” is “Push-to-Talk over Cellular”(POC) systems sometimes called “Global 2 Way” basically they were originally just cell phones that you don’t dial and have been around for nearly four decades.

Later as VoIP and data -IP over GSM became practical they moved into virtual networking. Then as WiFi / Bluetooth chips became inexpensive thay got added (see Zello and the like).

However POC are mostly still not true replacements for PMR and similar FM/AM/SSB voice based radio systems. Which is why now some POC handsets running Android also contain FM VHF or/and UHF two way radio modules covering the same range as the very inexpensive Chinese 2Way handsets like the UV5 etc. This is because they use the same “cheep as chips” radio modules.

In fact you can now buy modules yourself that stick on the back of any modernish Android phone so you can make your own POC+PMR/Ham for a lot lot less.

But even Amateur/ham is going digital in a slightly different way… Look up “Ham Hotspots” and Ham-VoIP systems. They use a traditional Ham Radio to work using low power to what is a combined “Software Defined Radio”(SDR) and Gumstick style “Single Board Computer”(SBC) to then work using VoIP and similar across the Internet and through satellites etc.

So the days of Mobile Phones and Walkie Talkies as distinct objects are coming to an end for “wide area use”. Nano, Pico, and Femto cell operation using GSM is one future path with personal HotSpots based on WiFi and similar being another. Thus the differentiation between Off Grid and On Grid communications will be very blured.

Which makes “effective EM jamming” not just difficult but near impossible except very very locally. Which means that in non battle field locations those desiring to jam individuals communications will, where they can, resort to knocking entities off at the backhaul or network backbone level.

The point is that “local communications” has become too diverse for traditional jamming in even military warfare. With well over 100MHz of bandwidth available for 4G and above with phased array antennas standard, effective jamming will require as much if not more radiated power as a radar unit. Which means the chances of getting a HARM missile as a greeting present winging in at near Mach 3 or a few 155mm artillery shells dropping in at upto Mach 2 is really quite high.

[] To find out more about HotSpots the easiest way is to read a “HowTo” build your based own on a common SBC

https://hagensieker.com/2024/04/13/best-dmr-hotspot/

[] Fun fact, we’ve all heard about “jam proof drones” that use fiber optics, and many have also heard of military “field telephones”. What killed of field telephones was putting the wire down as it was slow and dangerous work. Well someone has developed a low cost light weight field telephone that uses the same fiber optic cable as the drones do. So now the fiber and phone can be deployed by drone in just moments. Also someone has developed a very inexpensive optical fiber interface to the very inexpensive VHF and UHF radio and LoRa modules. Thus making shelling DF’d TX locations a waste of expensive ammunition (properly used RX only locations are difficult to find unless you literally trip over them as they can be smaller than trail-cameras or boxes of matches).