It's still vulnerable to a binary search to find an author: create an account with the first half of your contacts and another with the second half, see which a

It's still vulnerable to a binary search to find an author: create an account with the first half of your contacts and another with the second half, see which account has the secret (if it's in neither, it's from outside your network and you don't care) and repeat the process on that half. You'll figure the account with a dozen or two accounts created.