&gt; PFS requires synchronicity<p>No it doesn&#x27;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 (<a href="https:&#x2F;&#x2F;whispersystems.org&#x2F;blog&#x2F;private-groups&#x2F;" rel="nofollow">https:&#x2F;&#x2F;whispersystems.org&#x2F;blog&#x2F;private-groups&#x2F;</a>)<p>Now, that doesn&#x27;t mean it already works in Signal&#x2F;Whatsapp, because they have other constraints. But it&#x27;s not PFS that prevents it.