Key Exchange

Abstract

This chapter explains the elements of key exchange, specifically the steps in a key exchange protocol, the parties that are involved and the messages which may be sent. It details key exchange security models and protocols, considering first the simpler case of unauthenticated key exchange before turning to authenticated protocols. The chapter deals with key exchange protocols designed to be secure against a passive adversary. It examines that unauthenticated protocols may be used as building blocks for authenticated key exchange protocols. Key exchange protocols that allow parties to verify the identity of other participating parties are called authenticated key exchange protocols. Key exchange has a long history and a vast literature, yet remains a very active research area with significant practical impact. It is inevitable that as new computational assumptions emerge as the basis for cryptographic security, so will their use in key exchange be relevant.