Technically, if you squint hard enough, and assuming that Bit.ly always shortens the same URL to the same code (which on my brief testing it did when I tried the same URL from two different browsers), a one-way hashing function is being created from bit.ly shortened URLs -> the full "hashed" document. Technically. It certainly lacks most of the usual properties we associate with hash functions but the bare skeleton is sort of there. And there's no way to feasibly reverse that hash function algorithmically short of keeping the original input table and querying that, which is how Bit.ly of course works.