On security enhancement of long-term private key for the tripartite authenticated key agreement protocol

In this paper, we propose a scheme that enhances the security of long-term private key l_ID used in the tripartite authenticated key agreement protocol. In this scheme, we use (H(l_IDPmacr)l_ID)P (H: hash function) instead of l_IDP (P: a rational point of the defined elliptic curve over F_p) as a static public key and tau_ID1, tau_ID2 as two ephemeral private keys. From this, even though the bit length of p (p´s security parameter) is more lessened, we can preserve equal security to conventional schemes in respect of the secrecy of the long-term private key.