Use of hashes

The hashes used are md5 hashes where the first 7 chars are converted into an integer which is used as the hash in the database. This is done in order to save space in the database, thus using only 4 bytes and not a varchar of 32 bytes. It's estimated that a hash of 7 chars (32) is sufficient (originally 8, but at some point PHP changed behavior with hexdec-function so that where originally a 32 bit value was input half the values would be negative, they were suddenly positive all of them. That would require a similar change of the fields in the database. To cut it simple, the length was reduced to 7, all being positive then).