Liu, HongVasserman, Eugene Y.Hopper, Nicholas2015-08-052015-08-052013-11-04http://hdl.handle.net/2097/20141Off-the-Record Messaging (OTR) is an online analogy of face-to-face private chat { messages are confidential and au- thenticated at the time of the conversation, but cannot later be used to prove authorship. The original OTR protocol is limited to two parties, and is extended by multi-party OTR (mpOTR) to the group chat setting. In doing this, mpOTR unintentionally weakens the security properties provided by its two-party predecessor. We propose an improved group OTR (GOTR) protocol that provides unconditional repudi- ability, and show how to obtain data origin authentication given this level of repudiability. GOTR resists network failure, colluding and independent malicious insiders, and provides efficient and exible mem- bership management. We analyze the security properties and performance of GOTR, and present measurement re- sults of a proof-of-concept implementation of GOTR.en-USThis Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).PrivacyRepudiabilityGroup communicationAuthenticationRobustnessText