ABSTRACT
An important concept in theoretical computer science is hash functions. To give just one example, when a long document is to be signed electronically, one applies at first a hash function to produce a much shorter string (a digest of the original document) and then applies the signature scheme to this hash value. The notion of a hash function is very problematic. Universal hashing was designed to find a way out of this dilemma, at least for certain applications. Just as for hash functions themselves, there are numerous variants.
