The are not secret and not unguessable, they use some homegrown cipher, calling the result of encryption a &quot;hash&quot; for some reason (<a href="http:&#x2F;&#x2F;carnage.github.io&#x2F;2015&#x2F;08&#x2F;cryptanalysis-of-hashids&#x2F;" rel="nofollow">http:&#x2F;&#x2F;carnage.github.io&#x2F;2015&#x2F;08&#x2F;cryptanalysis-of-hashids&#x2F;</a>)