Entity Authentication and Key Distribution

Entity authentication and key distribution are central cryptographic problems in distributed computing|but up until now, they have lacked even a meaningful de nition. One consequence is that incorrect and ine cient protocols have proliferated. This paper provides the rst treatment of these problems in the complexity-theoretic framework of modern cryptography. Addressed in detail are two problems of the symmetric, two-party setting: mutual authentication and authenticated key exchange. For each we present a de nition, protocol, and proof that the protocol meets its goal, assuming the (minimal) assumption of pseudorandom function. When this assumption is appropriately instantiated, the protocols given are practical and e cient.