It&#x27;s not a forking attack, it&#x27;s a selective-lying attack -- a malicious Keybase server could serve up old versions of someone&#x27;s files, or pretend that e.g. no shared files exist between you and another user even though they do.<p>Putting everything into Merkle trees with published updating hashes allows clients to catch a malicious server -- if the server wants to lie to someone (without being caught), it has to lie to everyone at once.