Great question, thanks. If the Verifiable Identifier is not salted first, and the attacker is determined to match a particular domain to a hash in a rainbow ta

Great question, thanks. If the Verifiable Identifier is not salted first, and the attacker is determined to match a particular domain to a hash in a rainbow table of hundreds of millions of email addresses / phone numbers, then the answer is yes. So worst case scenario, this could be a way for a bad actor (e.g. a state) to track down the journalist that runs a blog that's critical of a regime. However, people like that would not opt-in to a Domain Verification record in the same way that they don't opt in to having their details published to the website / WHOIS. So I don't think this is a real risk. The bigger rainbow table risk is mitigated by the hash being used in the DNS label. As an example, if the hashed verifiable identifier was simply stored in TXT at: _dv.example.com Then it would be trivial to harvest e.g. 100m Domain Verification records and then match those hashes against a rainbow table (e.g. 500m hashed emails). However, since the hash is used in the label so you would need to run 500m DNS queries per domain (one for each rainbow table hash).