A Pairing-Free, One Round Identity Based Authenticated Key Exchange Protocol Secure Against Memory-Scrapers

Security of a key exchange protocol is formally established through an abstract game between a challenger and an adversary. In this game the adversary can get various information which are modeled by giving the adversary access to appropriate oracle queries. Empowered with all these information, the adversary will try to break the protocol. This is modeled by a test query which asks the adversary to distinguish between a session key of a fresh session from a random session key; properly guessing which correctly leads the adversary to win the game. In this traditional model of security the adversary sees nothing apart from the input/ output relationship of the algorithms. However, in recent past an adversary could obtain several additional information beyond what he gets to learn in these black box models of computation, thanks to the availability of powerful malwares. This data exfiltration due to the attacks of Memory Scraper/Ram-Scraper-type malwares is an emerging threat. In order to realistically capture these advanced classes of threats posed by such malwares we propose a new security model for identity-based authenticated key exchange (ID-AKE) which we call the Identity based Strong Extended Canetti Krawzyck (ID-seCK) model. Our security model captures leakages of intermediate values by appropriate oracle queries given to the adversary. Following this, we propose a round optimal (i.e., single round) ID-AKE protocol for two-party settings. Our design assumes a hybrid system equipped with a bare minimal Trusted Platform Module (TPM) that can only perform group exponentiations. One of the major advantages of our construction is that it does not involve any pairing operations, works in prime order group and have a tight security reduction to the Gap Diffie Hellman (GDH) problem under our new ID-seCK model. Our scheme also has the capability to handle active adversaries while most of the previous ID-AKE protocols are secure only against passive adversaries. The security of our protocol is proved in the Random Oracle (RO) model.