[bhawks]

Those hash functions are (or were) cryptographically secure. They aim to prevent many different kinds of attacks that may be launched on hashed data. There are many other noncryptographic ways to use hashes (like writing your own dictionary) that do not need the protections cryptographic hashes give you and therefore can trade those protections for performance.

Pairwise independence basically means that applying 2 different hash functions to the same key produces 2 distinct/seemingly random values. There's a much more precise mathematical definition but that's the essence.