Off-the-Record Messaging

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  • otrv4

    Off-the-Record Messaging Protocol version 4. -This is a draft- This repository is a mirror of http://bugs.otr.im/otrv4/otrv4

    I may have missed something here, but the write-up seems to be missing the main problem with OTR, which is that both parties need to be online at the same time to do the key-exchange to set up the session - at least in OTRv3 (https://otr.cypherpunks.ca/Protocol-v3-4.0.0.html)

    This is why the Double Ratchet Algorithm was created (back in 2013!) where you prepublish a pool of one-time-keys which can be used to establish sessions without you having to be online - as well as defining how to ratchet the message keys forwards both by new DH exchanges and simple hash ratchets (hence the name Double Ratchet).

    OTRv3 has the sole advantage that you can trivially tunnel it over any existing synchronous transport (e.g. an IRC DM), given it doesn't have the concept of setting up sessions asynchronously. However, this is a bit of a moot point these days, given modern messaging systems like Matrix, XMPP and Signal natively support the Double Ratchet via Olm, OMEMO & libsignalprotocol respectively - so OTRv3 really is a bit of a historical curiosity at this point.

    Meanwhile OTRv4 does introduce the idea of offline conversation initialisation (https://github.com/otrv4/otrv4/blob/master/otrv4.md#offline-...), but it doesn't seem to have got much traction, relative to the fairly ubiquitous Double Ratchet. (Has anyone seen it in the wild? It looks like coy.im might speak it? https://github.com/otrv4 seems fairly dead :/)

    Finally, lots of E2EE research is going into efficient shared ratchets for group communication rather than 1:1 sessions - such as MLS (https://datatracker.ietf.org/wg/mls/about/), DMLS (https://matrix.uhoreg.ca/mls/decentralised.html) and DCGKA (https://www.cylab.cmu.edu/news/2021/11/23-group-messaging.ht...).

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NOTE: The number of mentions on this list indicates mentions on common posts plus user suggested alternatives. Hence, a higher number means a more popular project.

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