Law Enforcement Access to Chat Data and Metadata
I don’t see a lot of surprises in the document. Lots of apps leak all sorts of metadata: iMessage and WhatsApp seem to be the worst. Signal protects the most metadata. End-to-end encrypted message content can be available if the user uploads it to an unencrypted backup server.
EDITED TO ADD (12/13): Here’s a more legible copy of the text.