Thanks for the link. Awhile back, I had implemented an n-bit cipher (where 1 <= n <=64) with an unbalanced Feistel network and used hash function as the basis of the round functions. I then wrap it within a cycle-walking function to form a cipher for any number smaller than 2^64. I did all this so I can generate scrambled 5-char path IDs of short URLs (e.g. test.com/xA7bc) with domain size of 62^5.
http://www.cs.ucdavis.edu/~rogaway/papers/subset.pdf
(Marsh Ray tweeted this yesterday; it's an easy read)