Do you generate a random key for each id? If so, you loose the time component of your I'd, because two hashes made at a different time can produce the same hash

Do you generate a random key for each id? If so, you loose the time component of your I'd, because two hashes made at a different time can produce the same hash when using a different key (I think). If you use a single key you need to manage it and keep it secret which isn't really ideal for something simple like id's. If you reveal the key you could as well use an unkeyed hash, right? Maybe a salted hash with the same salt for every key to make dictionary attacks on the creation time harder. But then again it's probably easier to just generate random bits for the id, as you don't have sortability in any case.