Advances in Cryptology — EUROCRYPT 2000

Volume 1807 of the series Lecture Notes in Computer Science pp 139-155


Authenticated Key Exchange Secure against Dictionary Attacks

  • Mihir BellareAffiliated withDept. of Computer Science & Engineering, University of California at San Diego
  • , David PointchevalAffiliated withDépt. d’Informatique-CNRS, École Normale Supérieure
  • , Phillip RogawayAffiliated withDept. of Computer Science, University of California at Davis


Password-based protocols for authenticated key exchange (AKE) are designed to work despite the use of passwords drawn from a space so small that an adversary might well enumerate, off line, all possible passwords. While several such protocols have been suggested, the underlying theory has been lagging. We begin by defining a model for this problem, one rich enough to deal with password guessing, forward secrecy, server compromise, and loss of session keys. The one model can be used to define various goals. We take AKE (with “implicit” authentication) as the “basic” goal, and we give definitions for it, and for entity-authentication goals as well. Then we prove correctness for the idea at the center of the Encrypted Key-Exchange (EKE) protocol of Bellovin and Merritt: we prove security, in an ideal-cipher model, of the two-flow protocol at the core of EKE.