Authenticated Group Key Agreement(AGKA) protocol allows a group of users in a public network to share a session key which may be used to achieve desirable secure communication.The protocol compiler proposed by Abdalla et al transforms any provably secure authenticated 2-party key establishment into a provably secure AGKE with two more rounds of communication.This paper points out an impersonation attack against the protocol compiler that two malicious users can impersonate an entity to agree some session keys in a new group if these two malicious users have the previous commitment transcripts of the entity.The improvement to eliminate the security leaks is proposed.
Authenticated Group Key Agreement(AGKA) protocol allows a group of users in a public network to share a session key which may be used to achieve desirable secure communication.The protocol compiler proposed by Abdalla et al transforms any provably secure authenticated 2-party key establishment into a provably secure AGKE with two more rounds of communication.This paper points out an impersonation attack against the protocol compiler that two malicious users can impersonate an entity to agree some session keys in a new group if these two malicious users have the previous commitment transcripts of the entity.The improvement to eliminate the security leaks is proposed.
Many conference systems over the Internet require authenticated group key agreement (AGKA) for secure and reliable communication. After Shamir [1] proposed the ID-based cryptosystem in 1984, ID-based AGKA protocols have been actively studied because of the simple public key management. In 2006, Zhou et al. [12] proposed two-round ID-based AGKA protocol which is very efficient in communication and computation complexity. However, their protocol does not provide user identification and suffers from the impersonation attack by malicious participants. In this paper, we propose improved ID-based AGKA protocol to prevent impersonation attack from Zhou et al.'s protocol. In our protocol, the malicious insider cannot impersonate another participants even if he knows the ephemeral group secret value. Moreover, our protocol reduces the computation cost from Zhou et al.'s protocol.
In modern network computing, authenticated group key agreement (AGKA) is important for conferencing. After Shamir [2] proposed the ID-based cryptosystem in 1984, the various applications on the ID-based cryptosystem have been actively studied, due to the simple key management complexity. For the AGKA, Choi et al. [16] proposed an ID-based authenticated group key agreement with bilinear maps, which was extended from Burmester and Desmedt conference key agreement protocol [5]. After that, Zhang and Chen [15] showed that the impersonation attack on Choi et al. protocol is feasible when two malicious users have the previous authentication transcripts of the entity. Shim [19] showed that the insider colluding attacks can be done without the previous transcripts. In this paper, we propose an improved ID-based AGKA. In our scheme, Key Generation Center (KGC) keeps the list of randomized user index instead of only generating private key. The random user indexing means KGC shuffles the order of users’ indices by randomizing to hide it so that the malicious users cannot know the order. KGC also verify all users than only verifies 3 users in Choi et al.’s protocol. Our protocol can prevent replay attack of Zhang and Chen and insider colluding attack of Shim.
An ID-based authenticated group key agreement (AGKA) protocol allows a group of members to share a key and provide an assurance of key sharing with an intended group with the user's identity, which is used for conferencing environments. In 2004, Choi et al proposed an ID-based authenticated group key agreement with bilinear maps (also called CHL protocols), which was extended from Burmester and Desmedt conference key agreement protocols. Unfortunately, their protocols were found to be vulnerable to the insider attacks in which cases that the two malicious users have the previous authentication transcripts of the party by Zhang, Chen and Shim. In this paper, we proposed an improved ID-based AGKA. In our scheme, each session has a unique session identity which is published by Key Generation Center. With such unique session identity binding to each session, our protocols can prevent the insider attack. Especially, our protocols can not enhance the computationally cost and it is still efficient.
In modern collaborative and distributed applications, authenticated group key agreement (AGKA) is one of the important issues. In this paper, we present that one existing certificateless AGKA protocol has some security drawbacks and does not satisfy some security attributes required for AGKA protocols. To overcome its drawbacks, we propose a secure and efficient protocol upon the initial one and a signature scheme proved secure in the random oracle model. The security analysis shows that our improved protocol can achieve Explicit key authentication, Known session key security, Known ephemeral secrets security, Perfect forward security, No key compromise impersonation, No key control and No unknown key share. With respect to efficiency, our protocol only needs three communication rounds. In each protocol run, only three pairing computations are involved for each participant.
With the development of multiuser online meetings, more group-oriented technologies and applications for instance collaborative work are becoming increasingly important.Authenticated Group Key Agreement (AGKA) schemes provide a shared group key for users with after their identities are confirmed to guarantee the confidentiality and integrity of group communications.On the basis of the Public Key Cryptography (PKC) system used, AGKA can be classified as Public Key Infrastructure-based, Identity-based, and Certificateless.Because the latter type can solve the certificate management overhead and the key escrow problems of the first two types, Certificateless-AGKA (CL-AGKA) protocols have become a popular area of research.However, most CL-AGKA protocols are vulnerable to Public Key Replacement Attacks (PKRA) due to the lack of public key authentication.In the present work, we present a CL-AGKA scheme that can resist PKRA in order to solve impersonation attacks caused by those attacks.Beyond security, improving scheme efficiency is another direction for AGKA research.To reduce the communication and computation cost, we present a scheme with only one round of information interaction and construct a CL-AGKA scheme replacing the bilinear pairing with elliptic curve cryptography.Therefore, our scheme has good applicability to communication environments with limited bandwidth and computing capabilities.
We present an efficient authenticated group key agreement (AGKA) protocol in certificateless public key setting (CL-AGKA). The protocol only needs two communication rounds. In each protocol run, only four pairing computations are involved for each participant. The authentication in our protocol is realized using a signature scheme which is provably secure in the strongest security model for certificateless signature (CLS) schemes where the type I/II adversary is a super type I/II adversary. The security analysis shows our protocol satisfies Key authentication, Known session key security, Key compromise impersonation security, Perfect forward security, and Known session-specific temporary information security.