Interestingly, since Onion addresses are derived from the public key of the host server, Facebook had to basically brute force this address.<p>The process is described in &quot;Part three&quot; here: <a href="https:&#x2F;&#x2F;blog.torproject.org&#x2F;blog&#x2F;facebook-hidden-services-and-https-certs" rel="nofollow">https:&#x2F;&#x2F;blog.torproject.org&#x2F;blog&#x2F;facebook-hidden-services-an...</a><p>&quot;The short answer is that for the first half of it (&#x27;facebook&#x27;), which is only 40 bits, they generated keys over and over until they got some keys whose first 40 bits of the hash matched the string they wanted.&quot;<p>&quot;Then they had some keys whose name started with &#x27;facebook&#x27;, and they looked at the second half of each of them to pick out the ones with pronouncable and thus memorable syllables. The &#x27;corewwwi&#x27; one looked best to them — meaning they could come up with a story about why that&#x27;s a reasonable name for Facebook to use — so they went with it.&quot;<p>(Corrected: Hash of public key not private key per itsbenweeks below)