&gt; &quot;As far as we can determine, practical privacy preserving contact discovery remains an unsolved problem.&quot;<p>This reminds me of an idea I had which I would love for people to tear apart (I know that the obvious bandwidth problem makes it completely impractical, but I wonder if there are theoretical flaws):<p>Have a central server which everybody connects to. All clients send a constant stream of data, 24&#x2F;7 - if they don&#x27;t have anything useful to send, they send &#x2F;dev&#x2F;random. When they do have something to send, they send a GPG public-key-encrypted message. Every client then receives the entire stream of data, handles the data which it can decrypt using its private key, and discards the rest.<p>- Your contacts list is a GPG keyring
- The server knows nothing
- Anyone intercepting your internet traffic can&#x27;t tell where your packets are destined for
- You can&#x27;t even look at two people&#x27;s traffic patterns and say &quot;these two people were active at the same time, they must be talking to each other&quot;