In this letter, we show that Chikazawa-Yamagishi ID-based key sharing scheme and its improved versions do not satisfy the forward secrecy. Also, we propose a modified version satisfying the forward secrecy.
The Chikazawa-Yamagishi scheme is an ID-based key distribution scheme which is based on the RSA cryptosystem. There are several variant schemes to improve the efficiency and the security of the Chikazawa-Yamagishi scheme. Unfortunately, all of the proposed schemes have some weaknesses. First, all the proposed schemes require time synchronization of the communicating parties. Second, none of the proposed schemes provide both forward secrecy and security against session state reveal attacks. In this paper, we suggest an ID-based key distribution scheme which does not require time synchronization and provides both forward secrecy and security against session state reveal attacks.
The security of a recently proposed ID-based authenticated key agreement protocol was analyzed. Although it is provably secure in the standard model, a malicious PKG (private key generator) can still obtain all of the agreed ses-sion keys, that is, it doesn’t provide PKG-forward secrecy in escrowless mode. To satisfy the security requirement in es-crowless mode, an improved version of the protocol was presented and it was proved to be a secure authenticated key agreement in the standard model. Results show that it provides perfect forward secrecy and PKG-forward secrecy.
유료 콘텐츠를 정당한 서비스 수신자에게 안전하게 제공하기 위해서는 서비스 제공자와 수신자 사이에 안전한 키 교환이 필요하다. 그룹 키 교환 프로토콜은 이러한 그룹에 속한 멤버들이 공개된 통신망을 이용하여 안전하고 효율적인 방법으로 그룹의 세션키를 설정할 수 있게 한다. 최근에 L. Zhou는 효율적인 인증된 그룹 키 교환 프로토콜을 설계하였다. 본 논문에서 우리는 Zhou의 기법이 전방향 안전성을 제공하지 않음을 보인다. An authenticated group key agreement protocol allows a group of parties communicating over an insecure network to share a common secret key. In this paper, we show that Zhou et al.'s ID-based authenticated group key agreement schemes do not provide forward secrecy.
In 2004, Hwang et al. proposed a group key exchange protocol for sharing a secure key in a group. Their protocol is an extension from the two party key exchange protocol to the group one. Recently, Jung-San Lee et al. noted that Hwang et al. group key exchange protocol has two security weaknesses. First, the forward secrecy is not confirmed in case that a new member joins the group and second, if a group member leaves the group, the backward secrecy is compromised. They proposed an improvement over this key exchange protocol in order to provide both forward and backward secrecy among group members. In this paper, we propose another improvement over Lee et al. key exchange, and we show that our key exchange protocol not only preservers both forward and backward secrecy, but also it is more efficient than their protocol when a member leaves the group. Finally, we give a formal analysis for the correctness of the proposed protocol via Scyther model checking tool.