A Shared-Key Security Protocol and Its Flaw

Abstract

Behaviour of cryptographic protocols is notoriously hard to understand because such a protocol is a concurrent process and can run with multiple instances in parallel. Such behaviour becomes more complicated because of malicious activities of attacker who is always assumed to be present in the environment of network. Being a public network (internet) it is very difficult to know who is who? Such threats need to be handled by a flawless security protocol which can guarantee to security of computer systems. In this paper we have analysed and compared the two versions (flawed and un-flawed) of NeedhamSchroeder Shared-Key (NSSK) protocol and have provided clear and detailed description to understand its flaw and how an unflawed version defeats an attacker.