Efficient multi-part chat

[elimisteve]

Multi-party chat currently exists, but it's very inefficient; a message is encrypted for every recipient individually (using the recipient's public GPG/PGP key).

Ideas:

1. Use AES (or similar) for multi-party chat, with the shared key exchanged behind the scenes via PGP
2. Consider implementing https://github.com/cryptocat/mpOTR, which would be ideal due to OTR's properties (e.g., perfect-forward secrecy).

In general, significant thought needs to go into determining the degree to which Cloakcast is a prototype merely meant to demonstrate the idea of decoys/decoy messages, or something more serious that will be maintained for years to come.