If you use a secure hash on the banned passwords they will be random (as good as arbitrary), then just truncate them to 7-8 bits and sort by prefix, searching them using binary search. It will be more efficient than a Bloom filter because there can be zero empty space between entries. It creates a structure similar to a Bloom filter but with no wasted space (no empty entries)

A Bloom filter is great when you need a probabilistic hash table that is fairly efficient and can have records added efficiently.

With a fixed list as I described above, the insertion cost is enormous (avg cost of moving 1/2 of the array elements), but the space/speed efficiency reaches the theoretical limit