They don&#x27;t like to admit it, but Signal has a metadata problem. It&#x27;s fine if that&#x27;s not their threat model, but I wish they would be more clear about it, especially when other chat systems get criticism more often for precisely that aspect.<p>Edit:
&quot;As far as we can determine, practical privacy preserving contact discovery remains an unsolved problem.&quot; -03 Jan 2014<p>[0] <a href="https:&#x2F;&#x2F;whispersystems.org&#x2F;blog&#x2F;contact-discovery&#x2F;" rel="nofollow">https:&#x2F;&#x2F;whispersystems.org&#x2F;blog&#x2F;contact-discovery&#x2F;</a><p>The kind of data they hold is legally within the reach of authorities and would allow metadata analysis similar to the NSA&#x27;s former phone metadata program.