Hash Function

Question 1

The properties which a hash function needs to process in order to be secure

Answer 1

Collusion resistance- impossible to find two distinct inputs that hash to the same value.
Preimage resistance - impossible to reverse the hash to find the original input.
Second preimage resistance - impossible to find a second, different input that has the same hash as a given input.

Question 2

Suppose that hash function H with output length n, what is the security level of H

Answer 2

N/2

Question 3

When was SHA-3 standardised by NIST

Answer 3

2015

Question 4

Two techniques used to design hash functions

Answer 4

Customised hash functions/ merkle damgard construction

Block cipher based hash functions

Question 5

Explain why the security of hash functions is 2^n/2 and not 2^n where n is the length of the hash output

Answer 5

The probability of finding a match increases as more and more hashes are generated.
After approximately 2^n/2 random inputs there is a 50% chance of a collision occurring

Question 6

Two principle modes of SHA-3 Hash Function usage

Answer 6

Hashing mode (fixed length output)
Extendable output function (XOF) mode