Identity-based key agreement protocols in a multiple PKG environment

To date, most identity-based key agreement protocols are based on a single PKG (Private Key Generator) environment. In 2002, Chen and Kudla proposed an identity-based key agreement protocol for a multiple PKG environment, where each PKG shares identical system parameters but possesses a distinct master key. However, it is more realistic to assume that each PKG uses different system parameters. In this paper, we propose a new two party key agreement protocol between users belonging to different PKGs that do not share system parameters. We also extend this protocol to a tripartite key agreement protocol. Our two party protocol requires the same amount of pairing computation as Smart's protocol for a single PKG environment and provides PKG forward secrecy. We show that the proposed key agreement protocols satisfy every security requirements of key agreement protocols.