Please help with A, B and C. Full and good answer will be upvoted.

Problem 3 Cryptography a) Block cipher usually processes a block of input at a time. Can a block cipher be used to encrypt a plaintext which is shorter than one block size? If yes, how is that done? b) To have secure communication, the communication parties must share a secret key first (using symmetric key cryptography). Suggest a scheme that can help the secure distribution/sharing of secret keys. c) Explain why public key cryptography is seldomly directly used in data encryption