[E2ee] Reducing Plaintext Metadata in E2EE Systems

[Matthew Finkel <[e-mail]>]

Hi all,

This draft is very valuable, thanks to the authors for writing it. I'd
like to call more attention to the importance of reducing plaintext
metadata. The current draft contains:

   Existing protocols are vulnerable to meta-data analysis, even though
   meta-data is often much more sensitive than content.  Meta-data is
   plaintext information that travels across the wire and includes
   delivery-relevant details that central servers need such as the
   account identity of end-points, timestamps, message size.  Meta-data
   is difficult to obfuscate efficiently.

The phrasing of this paragraph leads me to wonder if obfuscation of
metadata should be included as a desirable feature. I don't mean to
imply it's possible to eliminate leaking all metadata in all E2EE
systems, but there is often some low-hanging fruit, like IP addresses or
non-routing metadata, that an E2EE system can try to protect or
obfuscate; e.g., MASQUE/OHTTP/Tor for IP addresses, and [0][1] for
protecting some extraneous message headers. I can open a PR if this is
helpful.

Thanks,
Matthew Finkel

[0] https://datatracker.ietf.org/doc/html/draft-autocrypt-lamps-protected-headers
[1] https://signal.org/blog/sealed-sender/