What characteristic are needed to secure hash function?

1. H can be applied to a block of data of any size.

2. H produces a fixed-length output.

3. H(x) is relatively easy to compute for any given x, making both hardware and

software implementations practical.

4. For any given value h, it is computationally infeasible to find x such that H(x)

= h. This is sometimes referred to in the literature as the one-way property.

5. For any given block x, it is computationally infeasible to find y ≠ x with H(y) =

H(x).

6. It is computationally infeasible to find any pair (x, y) such that H(x) = H(y).