Man-in-the-middle (MITM)Attack on Version 4 Alice I am Robert I am Alice Bob Robert A n (n,KarPRA PUR Now,Robert knows Ka {(n KarpRA)PUn When Alice begins to talk to Robert,Robert starts to talk to Bob as Alice. Question:How to fix this problem? -Solution 1:use {fn,Kar}PURPRA to replace {fn,Kar)PRA)PUR - Solution 2:use {(n,R,Kar)PRA}PUR to replace {n,KarPRA)PUR Principle:Encryption should be inside a signature,otherwise we need to include principal's names. 99 Man-in-the-middle (MITM) Attack on Version 4  When Alice begins to talk to Robert, Robert starts to talk to Bob as Alice.  Question: How to fix this problem? ─ Solution 1: use {{n, Kar}PUR}PRA to replace {{n, Kar}PRA}PUR. ─ Solution 2: use {{n, R, Kar}PRA}PUR to replace {{n, Kar}PRA}PUR.  Principle: Encryption should be inside a signature, otherwise we need to include principal’s names. A n {{n, Kar}PRA}PUR Alice Bob A n Robert {{n, Kar}PRA}PUB Now, Robert knows Kar I am Robert I am Alice