toffi-fee

That's why I mentioned the multiple parties. But I understand your point. It would just be the next step for them to sneak in all kinds of words.

Stupid question: Wouldnʼt it be alright if an open source messenger scans messages locally against a secret word list and only sends it to police if there's a hit, otherwise only send it to the recipient with the usual end-to-end encryption?

The secret word list would need to be curated and digitally signed by several parties, including data security advocates to ensure that it doesn't simply contain the entire dictionary.

But the provision of the service is not made dependent on the consent if you can alternatively pay the monthly subscription. So I would assume, “accept all cookies or enter paid subscription” is Gdpr compliant.