I wonder, would E2E rotc13 count as illegal? What about the old method of both users having the same copy of a book and sending lookups of particular letter and

I wonder, would E2E rotc13 count as illegal? What about the old method of both users having the same copy of a book and sending lookups of particular letter and words. Where do you draw the line on banned algorithms? Where do you draw the geographical line? Would people in the UK no longer be allowed to communicated with someone in the US if that other person would only use E2EE?