Problem
Suppose, a network consists of four different nodes (A, B, C and D). How many keys do they have to generate such that A, B and C can communicate with D in a bidirectional secure way using the DES algorithm? How many keys do they have to generate such that every pair of nodes can communicate in a bidirectional secure way using the same algorithm? How many keys do they need to generate for both scenarios while using 3DES algorithm?