What is the purpose of these squiggly traces?

[unbuildpain]

Something along the lines of my suspicion:

[2012.06884] AIR-FI: Generating Covert Wi-Fi Signals from Air-Gapped Computers

Apparently memory buses do radiate EMF, strong enough to be received from few meters away, and the physical metal box doesn't block at all.

Now imagine what the traces near the audio chip can do.

If delay is the main reason squiggly traces are used, why can't they use some other shape, like zigzag, squares, rectangles, etc?

 

[betwixt]

Yes, signals can be picked up several meters away in 'air-gapped' situations but assuming your computer has a 32 or 64 bit memory bus, ALL those tiny signals are received simultaneously and at the same frequencies. SOME of that MAY fall into the WiFi band, any spectrum analyzer would demonstrate that easily but none would be able to reassemble any data from it.

Think of it like this, place 64 radios in a room, all tuned to different stations and all at the same volume. Now place a single microphone outside the room in a noisy environment but within hearing range. Would it be possible to clearly recover each and every sound from each station independently of the others? I think not. Now consider the sounds are not at low audio frequencies but at hundreds or thousands of times higher so the processing would have to be that much faster to recover anything. Bear in mind also that the memory bus is only one of many sources of signal that would be 'heard' simultaneously.

'Squiggly' traces are used for a simple reason: whenever a signal hits a change in track width, some of it gets reflected back to its source, using rounded bends allows the track to keep a constant width so reflections are minimized. Think about it, the reason for the squiggles is to help create a delay, if reflections occur they would be out of step with the 'outgoing' signal and risk corrupting it.

Now imagine what the traces near the audio chip can do.

Do some math - the optimum track lengths to radiate at WiFi frequencies is about 62.5mm for 2.4GHz band and about 29mm for 5GHz band. For mid range audio of say 1KHz, the optimum length is 150Km ! I doubt there is that much wiring in your whole house, maybe the whole street!

Brian.

 

[KlausST]

Hi,

In addition to Brian:
* You need a shielded room, else the WiFi of your neighbours and any other "true" HV signal would "overwrite" the tiny signals.
* you need a dedicated software on your PC...to
* No other software (no HMI driver, no OS, no software clock, ..)may run on the PC, else the other thread will use the SDRAM, too. Reading/writing random data.
* the address lines will cause noise in the same spectrum as the data lines...as they are routed almost identical to the data lines...and need to be controlled with the same timing as the data lines
* any other periferal will radiate signals (USB, monitor, graphics card, Ethernet, SDD, HDD, power supply

I don't say it is impossible.
But it's a challenge. You need to know the exact hardware, you need to have full software control, you need to have clean environment, you need a lot of effort...the useful data rate is low, the error rate will be high...

It's like playing music with a needle printer. Look for youtube videos.
You need the exact hardware, maybe you need to do modifications, maybe need a new controller..

Klaus