Towards Modelling Perfect Forward Secrecy for One-round Group Key Exchange

We propose two security models for one-round group key exchange (ORGKE), which are called as g-eCKw and g-eCK-PFS. The g-eCK-PFS is a stronger variant of geCKw, which particularly formulates perfect forward secrecy for ORGKE. A new tripartite ORGKE is proposed to provide g-eCKw security without random oracles under standard assumptions, that is also more efficient than its predecessor by Li and Yang on CANS’13. We also show how to transform (compile) a g-eCKw secure protocol to achieve g-eCK-PFS security. In particular, our result enables us to prove the security of the first ORGKE protocol that achieves perfect forward secrecy without random oracles in a strong security model allowing adversary to compromise critical information of session participants such as long-term or ephemeral private key.