Why Whittaker functions are useful?

Why aren't cryptographic hash functions used in data structures?

• While some algorithms like MD5 haven't quite stood the test of time with regards to the security industry, others like the SHA family of functions have (thus far). Yet despite the discovery, or theoretical existence of collisions within their domains, cryptographic hash functions still provide an incredibly well distributed range of fixed length output mappings for data of arbitrary length and type – why aren’t they used in data structures more often? Isn’t the goal of a hash table (provided a good function) to map every input to a unique key, such that chaining, nested tables and other collision handling techniques become entirely moot? It’s certainly convenient being able to feed almost anything to a function, and know the exact length of the key you will receive! Seems like an ideal use for retired security protocols to me.

• Answer:

  I would like to read other answers, as I'm not an expert. Cryptographic functions are stronger than general hash functions, in the sense that they don't only avoid collisions, but also don't reveal any information about the original text. This last constraint is not required for a hash function used in a hash table, for example. So, usually the hash functions for purposes other than cryptography are more efficient. Other point, which I think is more important, is that, for instance, SHA outputs a number that is 160-512 bits long. I don't see how can this be really useful for a hashtable, for example. Usually, hash functions for hashtables use the 'mod' operator in order to generate values that fit the table size. And that generates the collision problem. So, collision problem is, in my view, inherent to hashtables and not (totally) related to underlying hash function. Obviously that a good hash function would minimize such problem, but not eliminate it. (sorry for any english mistakes)