Research on Diffie-Hellman key exchange protocol

The purpose of the Diffie-Hellman protocol is to enable two users to exchange a secret key securely that can then be used for subsequent encryption of messages. The protocol itself is limited to exchange of the keys. But because of having no entity authentication mechanism, Diffie-Hellman protocol is easily attacked by the man-in-the-middle attack and impersonation attack in practice. In this paper, we compare the computational efficiency of various authentication methods. Finally an improved key exchange schema based on hash function is given, which improves the security and practicality of Diffie-Hellman protocol.

I. Introduction

Diffie-Hellman key exchange (D-H) is a cryptographic protocol that allows two parties that have no prior knowledge of each other to establish together a shared secret key over an insecure communications channel. Then they use this key to encrypt subsequent communications using a symmetric-key cipher. The scheme was first published publicly by Whitfield Diffie and Martin Hellman in 1976, Diffie-Hellman key agreement itself is an anonymous (non-authenticated) key-agreement protocol, it provides the basis for a variety of authenticated protocols, and is used to provide perfect forward secrecy in Transport Layer Security's short-lived modes as in [1]. In the original description papers, the Diffie-Hellman exchange by itself does not provide authentication of the communicating parties and is thus susceptible to a man-in-the-middle attack. An attacking person in the middle may establish two different Diffie-Hellman key exchanges, with the two members of the party “A” and “B”, appearing as “A” to “B”, and vice versa, allowing the attacker to decrypt (and read or store) then re-encrypt the messages passed between them. A method to authenticate the communicating parties to each other is generally needed to prevent this type of attack.