Off-the-record messaging

Version 4 of the protocol[3] has been in development since 2017[4] by a team led by Sofía Celi, and reviewed by Nik Unger and Ian Goldberg.

This version aims to provide online and offline deniability, to update the cryptographic primitives, and to support out-of-order delivery and asynchronous communication.

In 2005 an analysis was presented by Mario Di Raimondo, Rosario Gennaro, and Hugo Krawczyk that called attention to several vulnerabilities and proposed appropriate fixes, most notably including a flaw in the key exchange.

[5] As a result, version 2 of the OTR protocol was published in 2005 which implements a variation of the proposed modification that additionally hides the public keys.

[6] In 2007 Olivier Goffart published mod_otr[7] for ejabberd, making it possible to perform man-in-the-middle attacks on OTR users who don't check key fingerprints.

A method proposed in 2007 by Jiang Bian, Remzi Seker, and Umit Topaloglu uses the system of one participant as a "virtual server".

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.

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.