Version 4 A n Alice in,KabPRAJPUn Bob Kab denotes a session key Only Bob can decrypt{KU Denning Sacco "Time Stamps in Key Distribution Protocols"(1981) Question:What is wrong with this authentication protocol? Answer:vulnerable to man-in-the-middle attacks: 一 the attacker makes independent connections with the victims and relays/modifies/injects/deletes messages between them. 88 Version 4  Only Bob can decrypt {{n, Kab}PRA}PUB.  Denning & Sacco “Time Stamps in Key Distribution Protocols” (1981)  Question: What is wrong with this authentication protocol?  Answer: vulnerable to man-in-the-middle attacks: ─ the attacker makes independent connections with the victims and relays/modifies/injects/deletes messages between them. Alice Bob A n {{n, Kab}PRA}PUB Kab denotes a session key