Cryptology ePrint Archive: Report 1999/004
Public-key cryptography and password protocols
Shai Halevi, Hugo Krawczyk
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.
Category / Keywords: Passwords, Public-key protocols, Key exchange, Dictionary attacks, Password-guessing, Public passwords, Hand-held certificates.
Publication Info: Appeared in the THEORY OF CRYPTOGRAPHY LIBRARY and has been included in the ePrint Archive.
Date: received Feb 14th, 1999.
Contact author: shaih at watson ibm com
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