is complete, anyone is able to forge a message to appear to have come from one of the participants in the conversation, assuring that it is impossible to prove that a specific message came from a specific person. Within the conversation the recipient can be sure that a message is coming from the person they have identified. Authentication As of OTR 3.1, the protocol supports mutual authentication of users using a shared secret through the socialist millionaire protocol. This feature makes it possible for users to verify the identity of the remote party and avoid a man-in-the-middle attack without the inconvenience of manually comparing public key fingerprints through an outside channel. Limitations Due to limitations of the protocol, OTR does not support multi-user group chat but it may be implemented in the future. As of version 3 of the protocol specification, an extra symmetric key is derived during authenticated key exchanges that can be used for secure communication (e.g., encrypted file transfers) over a different channel. Support for encrypted audio or video is not planned. (SRTP with ZRTP exists for that purpose.) A project to produce a protocol for multi-party off-the-record messaging (mpOTR) has been organized by Cryptocat, eQualitie, and other contributors including Ian Goldberg. Since OTR protocol v3 (libotr 4.0.0) the plugin supports multiple OTR conversations with the same buddy who is logged in at multiple locations. Client support Native (supported by project developers) These clients support Off-the-Record Messaging out of the box. (incomplete list) Via third-party plug-in The following clients require a plug-in to use Off-the-Record Messaging. HexChat, with a third-party plugin Miranda NG (Microsoft Windows), with a third-party plugin Pidgin (cross-platform), with a plugin available from the OTR homepage WeeChat, with a third-party plugin HexChat, for *nix versions, with a third-party plugin Confusion with Google Talk "off the record" Although Gmail's Google Talk uses the term "off the record", the feature has no connection to the Off-the-Record Messaging protocol described in this article, its chats are not encrypted in the way described above—and could be logged internally by Google even if not accessible by end-users. See also References Further reading External links Protocol specification Off-the-Record Messaging: Useful Security and Privacy for IM, talk by Ian Goldberg at the University of Waterloo (video) Cross-platform free software Cryptographic protocols Cryptographic software Free security software Instant messaging Internet privacy software