Hi, paper author here :) thanks for providing a great answer to that question. I missed that the post/paper made its way to HN. One thing I'd add for the benef

Hi, paper author here :) thanks for providing a great answer to that question. I missed that the post/paper made its way to HN. One thing I'd add for the benefit of the discussion is that the term "metadata privacy" is rather fuzzy and different people mean different things with it. That's where some confusion can come from. I like to use "unobservable communication" to refer to absolute metadata privacy where no single bit of information is leaked - i.e. an adversary cannot even tell if any communication is happening at all at any point in time. For most real-world use-cases and threat models, this absolute privacy goal is often a bit unpractical because it comes with high latency or bandwidth needs. For instance, Tor is popular and practical because they prioritise latency and throughput with a careful threat model that excludes a global network adversary. However, the right threat model really depends on the individual use-case and circumstances. I think that Loopix (as linked above and what we use in our paper) does a great job in quantifying the achieved anonymity. See also https://bib.mixnetworks.org/pdf/serjantov2002towards.pdf https://bib.mixnetworks.org/pdf/serjantov2002towards.pdf for some more Information Theory in the context of Mix networks.