P2P chat that’s crackable, by layering random cyphers derived from the main key. The number of layers varies in a nondeterministic way, making each message cost between £10k and £10m to break, going up in powers of 2 in each layer.

If enough people use it, dragnet surveillance is impossible but serious investigations can get messages out as a proportion of spend. This gives the judiciary a way to say “if it’s that important, you fucking pay for it!” to law enforcement, preventing overreach.