Like always with Apple. But at least they’re saying they are doing it and supposedly detailing how.

Regarding the amount of secrecy on the how, it’s the way they do everything.

As for "sharing" the database of "forbidden content", freely or not, that would be sharing child pornography.

They can reveal the algorithm but this time abusers can find a way to change the information of an image to bypass the algorithm.

The most safe step is not to start this in the beginning because it will create more problems than it solve.

The secret threshold is a parameter in that protocol. It runs after the secret hash algorithm.