I read an article about securing databases. One of the methods that were described was a one-way function. Since f(x) is supposed to be "almost" impossible to convert back to x, this will make the database searchable & transparent @ the same time. Can someone pls clear up for me how is it guaranteed that the one-way function output [ f(x) ] is always unique. If f(x) is used as a search index is must be unique. What are the math techniques that make this happen?