Problem

(a) Using Vigenère cipher and given the key abc, find the ciphertext for the message:

simplicity

Only the 26 lower-case alphabetical characters are used in messages.

(b) Compare and contrast Data Encryption Standard (DES) with Advanced Encryption Standard (AES) with respect to:

(i) their classification
(ii) their encryption/decryption structure and algorithm
(iii) their cryptographic strength
(iv) types of attacks
(v) hardware/software implementation

(c) Consider a Diffie-Hellman scheme with a common prime q = 11 and a primitive root α = 2.

(i) If user A has public key YA = 9, what is A's private key XA?
(ii) If user B has public key YB = 3, what is the shared secret key K, shared with A?

(d) What are the characteristics of the ‘one-time pad' cryptosystem as compared to Vigenère Cipher.

Give one advantage and two problems with one-time pad cryptosystems.

(e) S/MIME (Secure / Multipurpose Internet Mail Extensions) is a standard for public key encryption and signing of e-mail encapsulated in MIME. What are the cryptographic security services for electronic messaging applications provided by S/MIME?