Abstract: Group Key agreement allows multi users to establish a common session key though insecure channels. Designing secure group key agreement protocols is one of the most fundamental cryptographic tasks. This paper introduced two approaches developed for analyzing security group key agreement protocols: computational complexity approach and formal analysis approach. The key technologies of computational complexity approach were discussed, including the proof technology based on reduction and simulatability, and security models based on reduction and simulatability. The trends in this field were presented.

Key words: Key agreement, Provably secure, Security model, Reduction, Simulatablility, UC framework