As a quick implementation note, we would not be using a hash for the IP address.
Most likely, we would encrypt the IP with AES or something using a configuration-based secret key. That way checkusers can still reverse the hash back into normal IP addresses without having to store the mapping in the database.
-- Tyler Romeo 0x405D34A7C86B42DF
From: Gilles Dubuc gilles@wikimedia.org Reply: Wikimedia developers wikitech-l@lists.wikimedia.org> Date: July 11, 2014 at 10:59:55 To: Wikimedia developers wikitech-l@lists.wikimedia.org> Subject: Re: [Wikitech-l] Anonymous editors & IP addresses
With hashing, a given IP would always give the same hash. So this uniqueness property would remain for people with stable IPs.