More Instant Messaging Interoperability (MIMI)
https://datatracker.ietf.org/doc/draft-barnes-mimi-arch/
The architecture document describes a federated system (with clients and servers), so it is a good starting point for designing E2EE in Fediverse. The architecture also seems to be compatible with FEP-e61.
MIMI specifies its own message format, which we probably don't need because we already have one. However, it might be a good idea to copy some parts
076萌SNS is a social network, courtesy of 076. It runs on GNU social, version 2.0.2-beta0, available under the GNU Affero General Public License.
All 076萌SNS content and data are available under the Creative Commons Attribution 3.0 license.