Cryptography & Network Security

User Authentication.

(b) Consider the following proposed authentication protocol between Alice and Bob based on asymmetric encryption which is supposed to establish a shared session key K between the two users. Alices public key is KA and Bobs public key is KB.

Show an attack against this protocol by demonstrating a scenario where Eve can impersonate Alice to Bob (i.e. Bob will think they are talking to Alice when they are in fact talking to Eve). Then provide a fix to the protocol to prevent this attack.

Alice Bob: {Alice, NA}KB Bob Alice : {K, NAHKA Alice + Bob : {Hello Bob! This is Alice, NAHK