Describe any THREE characteristics of what might be regarded as a good encryption algorithm. Two of the modes under which a symmetric encryption algorithm can operate are described by the following equations:

 

(i) Identify the modes of operation and explain the meaning of all terms in the above equations.

(ii) Explain why a practical implementation of mode (2) should require the use of mode (1) during the initial phase of the dialogue. [6 marks]

 

(c) Explain the meaning of the terms message integrity and authentication in the context of network security. Describe how public key encryption technology can be used to implement

(i) a message integrity protocol and

(ii) an authentication protocol.

Ci = Ek (Pi) (1) Ci = Ek (Pi@Ci-1) (2)