Retrotechtacular: How Solidarity Hacked Polish TV

In the 1980s, Poland was under the grip of martial law as the Communist government of General Wojciech Jaruzelski attempted to repress the independent Solidarity trade union. In Western Europe our TV screens featured as much coverage of the events as could be gleaned through the Iron Curtain, but Polish state TV remained oblivious and restricted itself to wholesome Communist fare.

In September 1985, TV viewers in the city of Toruń sat down to watch an action adventure film and were treated to an unexpected bonus: the screen had a brief overlay with the messages “Solidarity Toruń: Boycotting the election is our duty,” and “Solidarity Toruń: Enough price hikes, lies, repression”. Sadly for the perpetrators, they were caught by the authorities after their second transmission a few days later when they repeated the performance over the evening news bulletin, and they were jailed for four months.

The transmission had been made by a group of dissident radio astronomers and scientists who had successfully developed a video transmitter that could synchronise itself with the official broadcast to produce an overlay that would be visible on every set within its limited transmission radius. This was a significant achievement using 1980s technology in a state in which electronic components were hard to come by. Our description comes via [Maciej Cegłowski], who was able to track down one of the people involved in building the transmitter and received an in-depth description of it.

Transmission equipment seized by the Polish police.
Transmission equipment seized by the Polish police.

The synchronisation came courtesy of the international effort at the time on Very Long Baseline Interferometry, in which multiple radio telescopes across the world are combined to achieve the effect of a single much larger instrument. Before GPS made available a constant timing signal the different groups participating in the experiment had used the sync pulses of TV transmitters to stay in time, establishing a network that spanned the political divide of the Iron Curtain. This expertise allowed them to create their transmitter capable of overlaying the official broadcasts. The police file on the event shows some of their equipment, including a Sinclair ZX Spectrum home computer from the West that was presumably used to generate the graphics.

There is no surviving recording of the overlay transmission, however a reconstruction has been put on YouTube that you can see below the break, complete with very period Communist TV footage.

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Data Exfiltration With Broadcast Radio And CD-ROM Drives

The first music played on personal computers didn’t come out of fancy audio cards, or even a DAC. the first audio system in a personal computer was simply holding an AM radio up to the case and blinking address pins furiously. This worked wonderfully for homebrew computers where EMC compliance hadn’t even become an afterthought, but the technique still works today. [Chris] is playing music on the radio by sending bits over the system bus without using any wires at all.

[Chris]’ code is based on the earlier work of [fulldecent], and works pretty much the same. To play a sound over the radio, the code simply writes to a location in memory when the waveform should be high, and doesn’t when the waveform is low.

Of course the ability to exfiltrate information over an airgap has a few more nefarious purposes, but [Chris] also has another way of doing just that which is undefeatable by a TEMPEST shielded computer. He can send one bit at a time by opening and closing a CD-ROM drive, capturing these bits with a webcam. Is it useful? It’s hard to imagine how this setup could ever capture any valuable data, but it is a proof of concept.