What properties must a hash function have to be useful for message authentication?

Answer 1

To be useful for a message authentication, the hash functions must have the following properties –

• H can be applied to a block of data of any size

• H produces a fixed-length output

• H(x) is easy to compute for any given x, making both hardware and software implementations practical.

• For any given code h, it is computationally infeasible to find x such that H(x) = h. A hash function with this property is referred to as one-way or pre-image resistant.

• For any given block x, it is computationally infeasible to find y ≠ x with H(y) = H(x). A hash function with this property is referred to as second pre-image resistant. This is sometimes referred to as weak collision resistant.

• It is computationally infeasible to find any pair (x, y) such that H(x) = H(y). A hash function with this property is referred to as collision resistant. This is sometimes referred to as strong collision resistant.