A. Alice and Bob exchange confidential messages. They share a very large number as the encryption and decryption key in both directions. Is this an example of symmetric-key or asymmetric-key...

A. Alice and Bob exchange confidential messages. They share a very large number as the encryption and decryption key in both directions. Is this an example of symmetric-key or asymmetric-key cryptography? Explain.

B. Assume that we have a plaintext of 1000 characters. How many keys do we need to encrypt or decrypt the message in each of the following ciphers?

a. additive b. monoalphabetic c. autokey

C. According to the definitions of stream and block ciphers, find which of the following ciphers is a stream cipher.

a. additive b. monoalphabetic c. autokey