Multi-party key agreement protocols with cheater identification

In 2000, Pieprzyk and Li proposed two multi-party key agreement protocols based on secret sharing. The proposed protocols can achieve the following security goals: key freshness, key confidentiality, group authentication and key confirmation. However, this article points out that their protocols have a weakness for practical applications. A dishonest principal may disturb the protocol to fail, but anyone cannot identify the fraudulent principal. Therefore, an efficient cheater identification process is essential for multi-party key agreement protocols. Two improvements on their protocols are respectively proposed to remove this weakness. In our protocols, the extra computation overhead is small and security goals are not impaired.