(a) In the context of blockchain technology, answer the following questions: i. What is a digital signature? Assume Bob has created a transaction to send some money to Alice. Why should Bob put his digital signature along with his public key inside the transaction? ii. (6 marks) What is double spending? How it can be detected and prevented in a blockchain? iii. What is the 51% attack? How does it work? (4 marks) (4 marks) iv. Explain how malicious nodes (inside the blockchain's peer-to-peer network) are prevented from tampering with transactions using cryptographic hash functions. Assume each transaction contains the digital signature as well. (4 marks) V. Name and describe TWO applications other than cryptocurrency for blockchain. (2 marks) vi. What does the immutability of the blockchain mean? (2 marks) (b) Assume Bob has designed a hash function as follows: His function gets the data to be hashed. 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 [3 marks].