The Problem with Perceptual Hashes

The technical challenges aside, I’m very disturbed that my device will be reporting me to the authorities.

That’s very different from authorities taking a sneak peek into my stuff.

That’s like the theological concept of always being watched.

It starts with child pornography but the technology is indifferent towards it, it can be anything.

It’s always about the children because we all want to save the children. Soon they will start asking you start saving your country. Depending on your location they will start checking against sins against religion, race, family values, political activities.

I bet you, after the next election in the US your device will be reporting you for spreading far right or deep state lies, depending on who wins.

I’m big Apple fanboy, but I’m not going to carry a snitch in my pocket. That’s “U2 Album in everyone’s iTunes library” blunder level creepy with the only difference that it’s actually truly creepy.

In my case, my iPhone is going to be snitching me to Boris and Erdogan, in your case it could be Macron, Bolsonaro, Biden, Trump etc.

That’s no go for me, you can decide for yourself.

ah yes, from the same company that shipped this: https://medium.com/hackernoon/new-macos-high-sierra-vulnerab...

and this: https://www.theverge.com/2017/11/6/16611756/ios-11-bug-lette...

What? No...

Or, more accurately: if you need "dozens of trillions" that implies a false positive rate so low, it's practically of no concern.

You'd want to look up the poisson distribution for this. But, to get at this intuitively: say you have a bunch of eggs, some of which may be spoiled. How many would you have to crack open, to get a meaningful idea of how many are still fine, and how many are not?

The absolute number depends on the fraction that are off. But independent of that, you'd usually start trusting your sample when you've seen 5 to 10 spoiled ones.

So Apple runs the hash algorithm on random photos. They find 20 false positives in the first ten million. Given that error rate, how many positives would it require for the average photo collection of 10,000 to be certain at at 1:a trillion level that it's not just coincidence?

Throw it into, for example, https://keisan.casio.com/exec/system/1180573179 with lambda = 0.2 (you're expecting one false positive for every 50,000 at the error rate we assumed, or 0.2 for 10,000), and n = 10 (we've found 10 positives in this photo library) to see the chances of that, 2.35x10^-14, or 2.35 / 100 trillion.

So what are we going to do about it?

I have a large user base on iOS. Considering a blackout protest.

IMHO, Unless everything being E2E encrypted becomes the law we can’t do anything about it because that’s not Apple’s initiative but comes from people whose job is to know things and they cannot resist keeping their hands out of these data collecting devices. They promise politicians that all the troubles will go away if we do that.

Child pornography, Terrorism? Solve it the old way.

I don’t know why citizens are obligated to make their jobs easier.

We survived the times when phone calls were not moderated, we survived the times when signal intelligence was not a thing.