Question

(b) Assume Bob has designed a hash function as follows: His function gets the data to be nashed. Then, he flips a coin 256 times, so he generates a string of Hs (Heads) and Ts (Tails). He replaces H with 1 and T with 0 . After that, he writes the data along with the generated binary string which is 256 bits long in a database. Next time, his function searches the data first. If it finds the data inside the database, it immediately returns its binary string, otherwise, it will repeat the process of flipping the coin. Based on the different features that a cryptographic hash function should have [ 3 marks], explain if this function is a proper hash function or not [ 2 marks]? Examine at least THREE features

Answer 1

Bob's hash function does not meet the criteria of a proper cryptographic hash function since it lacks determinism, pre-image resistance, and collision resistance. It generates hash values based on random coin flips and stores them in a database, which negates the purpose of a hash function to compute unique and consistent outputs for any given inputs.

Step-by-step explanation:

Bob's hash function that relies on a process of flipping a coin 256 times to generate a string of '1's and '0's does not meet the standards of a proper cryptographic hash function. Cryptographic hash functions must have certain features, including determinism, pre-image resistance, and collision resistance.

• Determinism

A hash function should always produce the same output for the same input. Bob's function is not deterministic since it generates a new binary string each time it does not find the data in the database. This is not characteristic of a proper hash function, which should always return the same hash for identical inputs without using a database for storage.

• Pre-image Resistance

A hash function should make it difficult to reverse-engineer the original input from its output. Bob's function lacks this feature, as it is not computing the hash based on the data, but arbitrarily assigns a binary string through coin flipping. This does not provide any security or assurance that similar data inputs would result in significantly different hashes.

• Collision Resistance

To avoid different inputs producing the same output, a hash function must minimize the likelihood of collisions. Bob's function is susceptible to collisions since the binary strings are generated randomly and unrelated to the data being hashed. Also, the possibility of generating the same binary string for different inputs is non-negligible.