This is the Olm protocol by Matrix, which uses the Perrin-Marlinspike Double Ratchet described at [1], and makes some similar cryptographic decisions to the Signal Protocol, but has a different wire format. As complete protocols, Olm and the Signal Protocol started off close but have since diverged in a number and magnitude of ways that I lack the expertise to comment on. Nonetheless, here's the same thing directly out of both Arathorn and Moxie's mouths, devs of Matrix and Signal respectively [2].
Despite valiant efforts on many people's part to lessen the conflation and confusion of protocols, this happens a lot still, but we can all try to do our part to be as accurate as we can.
Despite valiant efforts on many people's part to lessen the conflation and confusion of protocols, this happens a lot still, but we can all try to do our part to be as accurate as we can.
[1] https://github.com/trevp/double_ratchet/wiki [2] https://news.ycombinator.com/item?id=11725652