Added javadoc.
Standardized the method name.
Renaming.
Renamed the version member.
Added extensive tests to secure HandshakeResponse. (HandshakeChallenge is not enough tested yet.)
Added javadoc.
Improved the method name Message.appendContent -> Message.putContent.
Renamed the participant to recipient in the Message class.
Added a constructor with the recipient to the Message class. Adapted the rest to this change.
Simplified the encrypt method and improved the tests to make sure that only the public key is needed to encrypt.