Provable Secure Encrypted Key Exchange Protocol Under Standard Model

Encrypted key exchange protocol’s goal is to establish a high secure key used for further encryption and authentication through a low secure password. Most existing encrypted key exchange protocols either lack security proofs or rely on the Random Oracle model. Compared with those protocols based on the Random Oracle model, provable secure EKE (encrypted key exchange) protocols have heavier computation burden and their descriptions are more complex, although they don’t need the Random Oracle model. Through introducing server’s public key and applying ElGamal encryption scheme and pseudorandom function ensemble, a provable secure encrypted key exchange protocol is designed from the protocol proposed by David P. Jablon in the paper of “Extended Password Key Exchange Protocols Immune to Dictionary Attacks”, and a proof is presented. Compared with the original protocol, this protocol only needs DDH (decisional Diffie-Hellman) assumption but not ideal encryption and Random Oracle model. Compared with other provable secure encrypted key exchange protocols, because this protocol doesn’t need CCA2 (chosen ciphertext attack-2) secure public encryption scheme, it can reduce the number of exponible computations and greatly simplify the protocol’s description. Specifically, this protocol reduces 73% of the exponential computations of KOY protocol, and reduces 55% of the exponential computations of the protocol proposed by Jiang Shao-Quan et al. in the paper of “Password Based Key Exchange with Mutual Authentication”.