Underclocking a baseband chip creates a stealth wifi channel


#1

Originally published at: https://boingboing.net/2019/01/09/underlocked-for-stealth.html


#2

Seems like it keeps the center frequency in the same place in the ISM band and presumably the EIRP is no bigger than a regular WiFi chip so it should be perfectly legal. This is what the ISM band is all about.

I’m disappointed that the article doesn’t mention throughput figures. I’m curious just how much performance you are sacrificing here. My gut says it’s probably a lot.


#3

but will it blend?


#4

This should be possible with most any digital comm chip, cellular, wired etc. It’s just modifying the envelope of the waveform, nothing more. As long as you’ve got matching sender and receiver best case all you lose is throughput, though other parts of the circuit like hardware-level filters may reduce signal quality and transmission range.


#5

I would guess that it’s not so much a linear tradeoff in bandwidth, as the performance drops off a cliff at a certain point.

The more interesting idea, for me, is wifi pirate radio (with full-width channels, in illegal bands, perhaps bands abandoned by obsolete analog technologies like UHF TV)


#6

Now, pipe this narrowband signal through a sender/receiver pair of well-tuned (in other words, properly made) cantennas. In some ways, that might be harder to intercept than a maser link! But doable with rather cheap, off-the-shelf components; not like masers are common at Best Buy/Newegg/Tiger Direct/etc. ^^’…


#7

Those UHF bands are being auctioned off, block by block, to the cellular carriers. TV broadcasting is getting scrunched into a smaller block of channels.


#8

This may be a slightly more sensitive cantenna. I found it looking to recycle/reuse old satellite dishes to make hot water for tea.

IANAEngineer but:


#9

Well, yeah, IF you have a nice parabolic dish rattling about xD. But cantennas have the “outrageously cheap” thing going for them, ya know? DIY, we’re talking US$10-15 for materials (antennas only, not any router/wifi hardware attached) to get 18-21 Db gain, using NO power.

A powered yagi setup may do a bit better, but also means more moolah + less fun setting it up! Plus, you know, it uses power, not so hot with a laptop.


#10

Or something similar enough to a dish:

Wi-Fry:

Pringles vs. other cans (of baked beans etc.):

Oh hey Make is in on it as well:

https://makezine.com/2015/02/04/six-homebrew-hacks-to-boost-your-wi-fi/


#11

The first cantennas, in fact, were Pringles cans. They’re not quite the proper dimensions but pretty close.


#12

Building wifi antennas is relatively easy, but ubiquiti (ubnt.com) sells wifi devices with directional antennas. Just plug them in and it works.


#13

Some years back, I built a pair of cantennas and played around with them a bit. One was made from the tin that came with bottle of Glenfarclas, and the other was I think a large Spaghetti-O’s can. At the time, there was a little coffee shop near me that inexplicably didn’t offer any Wi-Fi, but I was able to punch a link from home through two houses with the cantennas. I had a Proxim laptop Wi-Fi card that had an external antenna connector - that was real handy, but I discovered those connectors are quite delicate and don’t withstand very many cycles.

I was able to get about a quarter of a mile from home and still get a signal, provided I had a cantenna on both ends. I could have gone further if I played around with timings.


#14

About a hundred years ago [in internet time] my Austin friends discovered warchalking. They would drive around with their highly advanced laptops and see which coffee shops had the right kind of bandwidth–the free kind. Of course nowadays nearly all U.S. coffee shops have it.

Pringles cans fit in to their process. It was very educational. That was where I first learned how fragile wifi networks and nodes really were. (Today’s cell towers “providing coverage” in my area likewise underperform routinely, despite my changing networks. Oh well. The future ain’t what it used to be.)

To this day, I still prefer a wired web connection wherever possible. I realize I am a dinosaur because of this. Having to use a dongle to stick a CAT5 or 6 cable into a device make this clear. Cortana, Alexa, GoogleHome Assistant, Siri and their ilk just solidify my opinion, not to mention the rest of the IoT.


#15

This is usually referred to as “wardriving”, from my experience, although the term was overused so badly, it may have changed since.

You are also NOT a dinosaur for preferring ethernet over wifi; it’s way, WAY faster, plus MitM (Man in the Middle) attacks are nearly impossible, at least on your end.


#16

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