Secure Group Key Exchange Protocol

M. Choudary Gorantla

A group key exchange (GKE) protocol allows a set of parties to agree upon a common secret session key over a public network. In this thesis, we focus on designing efficient GKE protocols using public key techniques and appropriately revising security models for GKE protocols. For the purpose of modelling and analysing the security of GKE protocols we apply the widely accepted computational complexity approach. The contributions of the thesis to the area of GKE protocols are manifold. We propose the first GKE protocol that requires only one round of communication and is proven secure in the standard model. Our protocol is generically constructed from a key encapsulation mechanism (KEM). We also suggest an efficient KEM from the literature, which satisfies the underlying security notion, to instantiate the generic protocol. We then concentrate on enhancing the security of one-round GKE protocols. A new model of security for forward secure GKE protocols is introduced and a generic one-round GKE protocol with forward security is then presented. The security of this protocol is also proven in the standard model. We also propose an efficient forward secure encryption scheme that can be used to instantiate the generic GKE protocol. Our next contributions are to the security models of GKE protocols. We observe that the analysis of GKE protocols has not been as extensive as that of two-party key exchange protocols. Particularly, the security attribute of key compromise impersonation (KCI) resilience has so far been ignored for GKE protocols. We model the security of GKE protocols addressing KCI attacks by both outsider and insider adversaries. We then show that a few existing protocols are not secure against KCI attacks. A new proof of security for an existing GKE protocol is given under the revised model assuming random oracles. Subsequently, we treat the security of GKE protocols in the universal composability (UC) framework. We present a new UC ideal functionality for GKE protocols capturing the security attribute of contributiveness. An existing protocol with minor revisions is then shown to realize our functionality in the random oracle model. Finally, we explore the possibility of constructing GKE protocols in the attribute-based setting. We introduce the concept of attribute-based group key exchange (AB-GKE). A security model for AB-GKE and a one-round AB-GKE protocol satisfying our security notion are presented. The protocol is generically constructed from a new cryptographic primitive called encapsulation policy attribute-based KEM (EP-AB-KEM), which we introduce in this thesis. We also present a new EP-AB-KEM with a proof of security assuming generic groups and random oracles. The EP-AB-KEM can be used to instantiate our generic AB-GKE protocol.

Shao-feng DENG, Fan DENG, LI Yi-fa

Qingchao Yang, Jingjun Lou, Shuyong Liu +1 more

M. Choudary Gorantla, Colin Boyd, Juan Manuel González Nieto

Abstract. Constructingaoneround group key exchange (GKE) protocol that provides forwardsecrecy is an open problem in the literature. In this paper, we investigate whether or not the security of one round GKE protocols can be enhanced with any form of forward secrecy without increasing the number of rounds. We apply the key evolving approach used for forward secure encryption/signature schemes and then model the notion of forward security for the first time for key exchange protocols. This notion is slightly weaker than forward secrecy, considered traditionally for key exchange protocols. We then revise an existing one round GKE protocol to propose a GKE protocol with forward security. In the security proof of the revised protocol we completely avoid reliance on the random oracle assumption that was needed for the proof of the base protocol. Our security proof can be directly applied to the base protocol, making it the most efficient one round GKE protocol secure in the standard model. Our one round GKE protocol is generically constructed from the primitive of forward secure encryption. We also propose a concrete forward secure encryption scheme with constant size ciphertext that can be used to efficiently instantiate our protocol.

H. K. Pathak, Manju Sanghi

Tsu‐Yang Wu, Yuh‐Min Tseng

An authenticated group key exchange (AGKE) protocol allows participants to construct a common key and provide secure group communications in cooperative and distributed applications. Recently, Choi et al. proposed an identity (ID)-based authenticated group key exchange (IDAGKE) protocol from bilinear pairings. However, their protocol suffered from an insider colluding attack because it didn't realize the security issue of withstanding insider attacks. Withstanding insider attacks mean that it can detect whether malicious participants exist in the group key exchange protocol. Nevertheless, an AGKE protocol resistant to insider attacks is still unable to find “who are malicious participants”. In this paper, we propose an ID-based AGKE protocol with identifying malicious participants. In our protocol, we use a confirmed computation property to achieve identifying malicious participants. Certainly, it is also secure against insider attacks. In the random oracle model and under related mathematical hard problems, we prove that the proposed protocol a secure AGKE protocol with identifying malicious participants.