Question no 7.10
In the needham and shroeder authentication protocol with secret keys,explain why the following version of messange 5 is not secure :
A->B : {NB}KAB
The purpose of messange no.5 is for A convince B that KAB is fresh .B will be convinced if it knows that A has KAB (because it will know that A cannot be merely replaying overhead messages). The suggestion version of message no.5 is not secure because A would not need know KAB in order to send it,it could be sent by copying message 4
