It doesn’t end to end if, of course, Facebook can read the content. It also wouldn’t make sense to send data twice, and someone would discover something like that in no time.
In fact, since the source code is locked and alternate clients have been banned (as with WhatsApp, so was Signal until recently while they built their own crypto scam, although no alternate clients are accepted yet) there’s little you can say about it How much data is actually leaking or not. Fortunately, there are people who hack third-party chat protocols to get their own systems to talk to Facebook, so we hope any implementation issue will surface soon. Additionally, there are bug bonuses for this kind of thing that can make FB code research very profitable.
Despite Facebook’s flaws, this is of course an improvement to the existing system. It’s not Facebook’s advantage to lie about this so I’m skeptical about the actual impact of this on your privacy vis-à-vis Facebook (I suspect text-to-speech on your phone, which is collected locally as interest or something) Your privacy against governments and hackers is still of course protected Better.
I guess no one who uses Facebook to chat really wants to hide things from Facebook anymore. For Facebook users, this is great, and the rest of the world will remain as secluded as they did before.
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