[GhotiFish]

you know. It occurs to me that you could actually do this without storing the password in plaintext!

All you'd have to do is iterate every potential answer into a bloom filter and store that. The math gets a little hairy around the 50 character mark as you'd have 117600 operations to do to construct the bloom filter, and it gets worse if you expect more characters.

Here's how you would construct it.

For every 3 choose n of the password, insert a value of those 3 characters ("abc") + delimit (":") + the positions (1,2,4), You can't just insert the characters because the index of characters is part of the answer.

all you'd need to do is store... a ~1MB bloom filter per client. Huh, that number was bigger than I thought it would be.

Well nevermind. Fun thought though.

[Vexs]

Realistically you could also just limit it to the first 10 characters.