What is Cryptography? Distinguish between passive and active attacks.

What are the differences between message confidentiality and message integrity? Can you have one without another? Use the additive cipher with k = 5 to encrypt the plaintext "BU". Then decrypt the message to get the original plaintext.

Describe Diffie-Hellman key exchange. Let p = 23. g = 5. Alice picks a = 6, Bob picks b = 15. Find the shared key.

What is Digital Signature? How it can be implemented to provide message integrity service?

Explain the process of creating and verifying a digital signature using asymmetric key cryptography. Use a step-by-step example involving a sender and a receiver.