State which of the following statements are true and which are false, making sure that in each case you provide a brief justification for your answer (no marks will be awarded for answers that are not justified):

a. Key derivation is the process of withdrawing a compromised key. [1 mark]

b. Presenting a server's public-key certificate to a client provides entity authentication of the server. [1mark]

c. Bitcoin guarantees the origin of the blockchain by computing a MAC over the hash of all recent transactions. [1 mark]