OMEMO

OMEMO is an extension to the Extensible Messaging and Presence Protocol (XMPP) for multi-client end-to-end encryption developed by Andreas Straub. According to Straub, OMEMO uses the Double Ratchet Algorithm "to provide multi-end to multi-end encryption, allowing messages to be synchronized securely across multiple clients, even if some of them are offline".^[1] The name "OMEMO" is a recursive acronym for "OMEMO Multi-End Message and Object Encryption". It is an open standard based on the Double Ratchet Algorithm and the Personal Eventing Protocol (PEP, XEP-0163).^[2] OMEMO offers future and forward secrecy and deniability with message synchronization and offline delivery.

Logo of OMEMO

Features

In comparison with OTR, the OMEMO protocol offers many-to-many encrypted chat, offline messages queuing, forward secrecy, file transfer, verifiability and deniability at the cost of slightly larger message size overhead.^[3]

History

The protocol was developed and first implemented by Andreas Straub as a Google Summer of Code project in 2015. The project's goal was to implement a double-ratchet-based multi-end to multi-end encryption scheme into an Android XMPP-based instant messaging client called Conversations. It was introduced in Conversations and submitted to the XMPP Standards Foundation (XSF) as a proposed XMPP Extension Protocol (XEP) in the autumn of 2015 and got accepted as XEP-0384 in December 2016.^[1]

In July 2016, the ChatSecure project announced that they would implement OMEMO in the next releases. ChatSecure v4.0 supports OMEMO and was released on January 17, 2017.^[4][5]

A first experimental release of an OMEMO plugin for the cross-platform XMPP client Gajim was made available on December 26, 2015.^[6]

In June 2016, the non-profit computer security consultancy firm Radically Open Security published an analysis of the OMEMO protocol.^[7]

Client support

Selected clients supporting OMEMO (full list of clients also exists^[8]):

• BeagleIM (macOS)^[9]
• ChatSecure (iOS)^[10]
• Conversations (Android)
• Converse.js (Browser-based)^[11]
• Dino (Linux, macOS)^[12]
• Gajim (Linux, Windows, BSD)^[13][14]
• Kaidan (Linux)^[15]
• Movim (Browser-based)^[16]
• Psi via official plugin (Linux, Windows, macOS)^[17]
• Psi+ via official plugin (Linux, Windows, macOS, Haiku, FreeBSD)^[18]
• libpurple clients such as Pidgin or Finch via experimental plugin ^[19]
• Adium via an Xtra based on the libpurple plugin^[20]
• Profanity via experimental plugin (BSD, Linux, macOS, Windows)^[21]
• SiskinIM (iOS)^[22]

Library support

• Smack supports OMEMO using the two modules smack-omemo and smack-omemo-signal^[23]
• XMPPFramework (macOS, iOS, tvOS) ^[24] supports OMEMO via the OMEMOModule extension ^[25] when used in conjunction with the SignalProtocol-ObjC library.^[26]