International Association for Cryptologic Research

International Association
for Cryptologic Research


Paper: Public-key cryptography and password protocols

Shai Halevi
Hugo Krawczyk
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Abstract: We study protocols for strong authentication and key exchange in asymmetric scenarios where the authentication server possesses a pair of private and public keys while the client has only a weak human-memorizable password as its authentication key. We present and analyze several simple password protocols in this scenario, and show that the security of these protocols can be formally proven based on standard cryptographic assumptions. Remarkably, our analysis shows optimal resistance to off-line password guessing attacks under the choice of suitable public key encryption functions. In addition to user authentication, we enhance our protocols to provide two-way authentication, authenticated key exchange, defense against server's compromise, and user anonymity. We complement these results with a proof that public key techniques are unavoidable for password protocols that resist off-line guessing attacks. As a further contribution, we introduce the notion of public passwords that enables the use of the above protocols in situations where the client's machine does not have the means to validate the server's public key. Public passwords serve as "hand-held certificates" that the user can carry without the need for special computing devices.
  title={Public-key cryptography and password protocols},
  booktitle={IACR Eprint archive},
  keywords={Passwords, Public-key protocols, Key exchange, Dictionary attacks, Password-guessing, Public passwords, Hand-held certificates.},
  note={Appeared in the THEORY OF CRYPTOGRAPHY LIBRARY and has been included in the ePrint Archive. 10500 received Feb 14th, 1999.},
  author={Shai Halevi and Hugo Krawczyk},