system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How did "cheater boxes" (cable descramblers) allow you to watch premium TV channels for free?

I had a few friends who had one back in the 90's that allowed you to get HBO and pay-per-view without actually paying for it.  I always wondered how they work.
gpt
Way back when, television was an analog signal. More accurately, it was a *series* of analog signals that your 100%-analog color television could use to produce a picture. You have three signals for color (your TV only looked at one if it was black-and-white) and a "timing" signal that indicated when it should start drawing a new line. The "vertical hold" was a sometimes-manual synchronization to that signal.

"Scrambling" was really just that. Some of the signals were inverted, some of them were switched. But, fundamentally, you couldn't *add* in junk or actually do significant *math* to obscure the signal, because televisions simply didn't have the ability to un-do that and produce a working picture for your paying consumer. Likewise, before relatively powerful integrated electronics became available, it wasn't economically feasible to give a customer a powerful computerized set-top box just to watch some television.

So your "encryption" was a scheme with only a few variables. Throw off the synchronization here, swap a color field here, and it would make the picture "off" enough to be unwatchable. But, likewise, once someone figured out your mechanism, they just had to create a relatively simply "decoder" to bring that signal back.

TLDR: Analog encryption wasn't terribly complicated, but it was analog, so it required *hardware* as opposed to something digital, which might be more complex, but also could be done with a wider variety of hardware. Nowadays, everything is digital (because computing power, even for high-definition video, is so cheap) so analog encryption/decryption isn't a thing.