Signing posts, comments and likes is essential for federation. That way fake messages can be prevented. And it allows users to do their own calculation of what

Signing posts, comments and likes is essential for federation. That way fake messages can be prevented. And it allows users to do their own calculation of what to show in a feed. E.g. only likes by whitelisted people could be considered. It's technically not possible to avoid leaking private messages, but metadata like license and level of confidentiality in the posts should at least provide hooks for legal enforcement.