I don't care about their paranoia. Child abusers could just use NNCP with sneakernet. Convoluted, but it doesn't touch internet at all. Still, the media it's encrypted.

Or they could encode a PNG under a H264 frame almost invisible to the eye (1/60 frames per second) but extractable with precise time related commands with ffmpeg. No encryption, no nothing. But it's there.

Also, GPG existed since the 90's, and there are symetric encrypting tools (even simple ones) everywhere, such as age. Again, they could just use sneakernet and some USB media.

Then they could just share it in the clear, over any protocol they wanted. Once you can shift bits with ease (in a reversible way), it's game over. Split, dd, perl, cat. You get junk with ease and recover that junk with the same ease.

Xor as a pipe: https://unix.stackexchange.com/questions/398481/xor-a-file-a...

Then with split/cat you get a dumb xorg encryption in pieces but the data could be put under a sorted list in a txt file with sha512sums of each part so anyone concat(1)enates the pieces in the right order. See? Is not even an issue on having strong encryption.