There are multiple problems with this implementation btw, if that is what they're planning.
1) It has a very high false positive rate (particularly at scale, where any false positive rate would be prohibitive) and would chill free expression.
2) It would undermine trust in secure communications.
3) It would undermine secure communications and make people susceptible for bad actors.
4) It could be used for purposes other than looking for actual child abuse, or images of actual child abuse.