Abstract: This paper extended the definition of key-compromise-impersonate attack according to a new kind of identity-based key exchange protocol presented by Wang in 2007，then showed that this protocol can't resist the extending key-compromise-impersonate attack. This paper also conducted a detailed analysis on the flaw. To avoid this shortcoming, an improvement of the identity-based protocol was proposed based on the original scheme.

Key words: Identity-based cryptography, Authenticate key agreement protocol, Bilinear pairing, Impersonate attack