[jeztek]

In response to kba:

deadchat implements the latter option. The secret room key is shared using the RSA key exchange protocol but you're right, there's currently no way to guarantee that you're talking to who you think you are. User authentication is on the todo list.

I think there's still value in hiding the conversation from the server even if you must still trust the server to not behave maliciously. If some three-letter agency contacts the server operator asking for a back channel to listen in, he or she could respond that it's not possible without malicious intent towards a user:

http://www.macobserver.com/tmo/article/apples-imessage-encry...