I wonder how this is supposed to help Sky identify who the source is — it's a satellite broadcast, so they presumably can't overlay a different number on the screen for different subscribers?
The number isn't in the broadcast signal, it's overlaid by the decoding box. It's going to be a number tied to the unique viewing card number (which is tied uniquely to a subscriber).
That's what I would have thought but would mean the Sky rep in the link is flat-out lying. As mentioned below, it could help isolate groups of subscriptions and allow progressively tracking down individuals. He only claims that it's not tied to an individual subscription.
I wonder how easily the firmware can be downgraded (or downgraded) to remove that behaviour. Though as noted in the sibling thread, it's more likely easier to crop the video output.
Distinctly non-trivial. The receiver software is cryptographically signed and is heavily integrated with the conditional access system securing the underlying broadcast.
I'm only aware of one time that a legitimate box was encouraged to run a lightly-patched version of the software, and that involved a JTAG-type attack on a specific model of set top box. I believe that lesson has been learned in current models.
In Germany, almost no one uses Sky, and those who do, almost completely run patched boxes. It’s even easy to use one single subscription on thousands of boxes at the same time.
It'd probably be much easier to just blur the area of the image where they put it to be honest, I've seen this on streams before, they just blur the bottom corner where the number would show up.
Although the position of the number is (obviously) under the control of the platform operator, so could appear anywhere, for any amount of time, if they were so minded.
I wouldn't like to bet against the number appearing right in the centre of the screen for a fraction of a second, if there were any particularly high-value programming being illegally streamed.
That was actually my first thought when I saw the screenshot with the numbers near the top of the screen. Slice that part off, stream the rest.
A similar thing shows up on YouTube a lot, actually. People heavily crop uploads of copyrighted material to get around their content identification stuff.
I wonder if they also use something like Digimarc for a non-visible watermark? They could publicly credit the visible watermark as a distraction from the real technique.
That's exactly how it works. The numbers are hashed by the receiver and uniquely identify that particular viewing card, then displayed in a position selected by the channel operator, when triggered at a time of their choosing.
If one were so inclined, I imagine it could be done with dedicated hardware specifically made for generating the overlay. May not be worth the cost though.
The smart card has nothing like the power required to process video - but it doesn't need to. The Sky receivers are fortified sufficiently to make changing the firmware a distinctly non-trivial operation.
