Whatsapp and signal use the same encryption and the same messaging protocol.
Piece of advice: As far as tech is concerned, HN isn’t a place where you can get away with talking about things you don’t understand. You’ll far too often run up against people who have more expertise in what you write about than you have expertise brushing your teeth.
I know what I'm talking about, and I'm detecting some arrogance.
Also, it doesn't matter here, but where are you getting that WhatsApp and Signal use the same messaging protocol? Might be missing something, but I don't see that they both use XMPP, if that's what you mean.
Piece of advice: As far as tech is concerned, HN isn’t a place where you can get away with talking about things you don’t understand. You’ll far too often run up against people who have more expertise in what you write about than you have expertise brushing your teeth.