[Cryptography] TV set power correlates to TV channel?

[John Gilmore]

> Due to the power "optimization" in modern LED TV sets, you cannow correlate to near certainty which channel is being watchedbased solely on power consumption data.  That data is enoughto get you murdered in quite a few countries around the worldtoday; countries that show up on every cybersecurity firm's"best customer" list.
> http://www.tij.co.jp/jp/lit/an/slva474/slva474.pdf
> "High Efficiency AC-DC TV Power Solutions: Proposing anIntelligent LED Backlight Driving Scheme.  Application ReportSLVA74-July 2011"

I read the reference you provided, and it doesn't seem to say anything
to prove your point.

The TI application report suggests that the control circuitry for LED
TV sets will adjust the power draw based on the heat output of the
LEDs (to reduce their heat), based on the aging of the LEDs over time,
and based on the brightness setting (which might be set by a user or
perhaps by an ambient light sensor).  But I didn't see anything in the
report that discussed changing the LED power based on the signal being
displayed on the screen.  So I don't see how this report suggests that
"you can now correlate to near certanty which channel is being watched
based solely on power consumption".  What did I miss?

"LED" TVs really use the LEDs just for the backlight (older TVs used
fluorescent lights for backlighting).  The picture itself is formed by
an LCD (liquid crystal display) panel that sits in front of the
backlight.  LCD displays -- not their backlights -- do draw different
amounts of power at each instant, based on what fraction of the color
subpixels have their transistor driven to the voltage for black versus
the voltage for illumination.  For example, a small PixelQi laptop LCD
screen that I have the specs for, draws 199 mA at 3.3V when showing an
entirely black screen, and 280 mA at 3.3V when showing an entirely
white screen.  That power draw is inherent to how LCDs work, but
whether that effect would be visible at the AC power cord depends on
many factors -- and the Application Report isn't even about that.)

	John