> PFS requires synchronicity No it doesn't. Multiple devices is a special case of multiple recipients, which the Signal protocol handles (and I presume Whatsap

> PFS requires synchronicity No it doesn't. Multiple devices is a special case of multiple recipients, which the Signal protocol handles (and I presume Whatsapp does as well). See more details here (https://whispersystems.org/blog/private-groups/ https://whispersystems.org/blog/private-groups/) Now, that doesn't mean it already works in Signal/Whatsapp, because they have other constraints. But it's not PFS that prevents it.